On board diagnostic ii obd ii (compilado)

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This document is intended to help in the understanding of OBDII parameters, known as
‘PIDs’, and give them definition. It is intended to be only a basic, not a technical guide to
scantool data. These PIDS are used by the OBDII system and by scantools that interact
with the systems for diagnostics and system interrogation. PID stands for Parameter
Identification, and in practice is rather cryptic. The scantool, luckily, takes this cryptic, bit
and byte data shorthand and translates it for us, so it is more understandable.
Live Data Trigger Frame
PID Unit Frame
These are parameters specific to the scantool being used in this case, and are
not OBDII standard PIDs.
Fuel System 1 Status [Status 1 or Fuelsys1]
Fuel System 2 Status [Status 2 or Fuelsys2]
Returns either OL – for Open Loop, or CL – for Closed Loop
Tells whether fueling is currently based on O2 Sensors and the oxygen content
of the exhaust, [Closed Loop] or based on sensor inputs [Open Loop] due to
conditions; logged faults, cold engine or wide open throttle, for instance.
Calculated Load Value [CLV or Load_PCT]
Engine load is represented by a "Calculated load value" which refers to an
indication of the current airflow divided by peak airflow, where peak airflow is
corrected for altitude, if available. This definition provides a unitless number that
is not engine specific, and provides the system with an indication of the percent
engine capacity that is being used. (With wide open throttle as 100%).
Engine Coolant Temp [ECT]
Current engine coolant temp as measured by the ECT [Engine Coolant Temp
sensor]. Usually reported in Celsius degrees.
Short Term Fuel Trim-Bank 1 [STFT 1 or SHRTFT1]
Short Term Fuel Trim-Bank 2 [STFT 2 or SHRTFT2]
Immediate trim changes made to the fuel mapping in response to oxygen
changes in the exhaust. Base fueling [injection] map is contained in the ECM, if
changes are required, fuel is added or subtracted from the base. Shown in
percent, positive percentage is ADDING fuel, negative percentage is
SUBTRACTING fuel. Short term trims are lost at key off.
Long Term Fuel Trim- Bank 1 [LTFT 1 or LONGFT1]
Long Term Fuel Trim- Bank 2 [LTFT 2 or LONGFT2]
Long term changes made to the fuel mapping based on Short Term fueling
corrections. Example: Short Term remaining at plus 6% for an extended period;
Long Term Trim will increment by that percentage and Short Term will return to
zero. Long Term Trims are maintained in non-volatile memory at key off, and
therefore not lost.
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Engine RPM [RPM]
I think this one is self explanatory.
Vehicle Speed Sensor [VSS]
Returns current vehicle speed, usually shown in kph, but some scantools allow
selecting kilometers or miles per hour.
Ignition Timing Advance #1 [Sparkadv]
Shows current spark timing advance in degrees for cylinder #1. Most engines
with knock retard systems can retard timing for individual cylinders, however.
Intake Air Temp [IAT]
Returns current temperature of the air entering the induction system. Like ECT,
usually reported in degrees Celsius, but some tools allow selecting scale.
Air Flow Rate from Mass Air Flow Sensor [MAF]
Returns the ECM calculation of total air flow, based on MAF signal AND air
temperature [IAT]. Most systems list this in grams per second, g/sec.
Absolute Throttle Position [TP or ABS_TP]
Listed in percent, shows actual position of the throttle butterfly, as it is not directly
connected to any cable or other driver input.
Bank 1 -- Sensor 2 Volts [O2S12]
Bank 2 – Sensor 2 Volts [O2S22]
Voltage output of downstream [second] Exhaust Oxygen sensor. Varies between
.2v and .8v normally. Used mainly for monitoring exhaust catalyst function.
Bank 1 – Sensor 2 % [O2S12STFT]
Bank 2 – Sensor 2 % [O2S22STFT]
Returns an additional trim value to the ECM for extremely fine fueling corrections.
Not used except for later model years, 2006 and later. Generally not useful to the
novice.
OBD Requirements OBD and OBD2 [OBDSUP]
Returns information to define which OBD requirements the vehicle was designed
to meet; i.e. which OBD system is onboard.
01h : OBD II (California ARB) 08h : EOBD and OBD
02h : OBD (Federal EPA) 09h : EOBD, OBD and OBD II
03h : OBD and OBD II 0Ah : JOBD
04h : OBD I 0Bh : JOBD and OBD
05h : not intended to meet any requirements 0Ch : JOBD and EOBD
06h : EOBD (Europe) 0Dh : JOBD, EOBD, and OBD II
07h : EOBD and OBD II 0Eh-FFh : Reserved by SAE J1979
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Now, upstream Oxygen Sensors are a little more confusing. Earlier cars use upstream
units that are very similar to the downstream sensors, called zirconium dioxide sensors.
They are also referred to as ‘Heated Exhaust Gas Oxygen’ sensors, or HEGO sensors.
Their output signal is voltage just like the downstream; it swings from .2v to .8v about
15-18 times a minute normally. These were fitted to the AJ26 V8 and the first generation
S-Type, both V6 and V8.
Beginning with the AJ27 4.0L V8 in 1999 and the AJ33 4.2L V8 in 2003, the upstream
oxygen sensors operated differently. These are referred to as ‘wideband’ or ‘linear’
sensors. To add confusion, they are also called ‘Universal’ Heated Exhaust Gas
Oxygen sensors, or UHEGO. The signal PID for these sensors is CURRENT, in
milliamps or microamps as the case may be.
***Note: The six-cylinder AJ16 engines utilize a different, Titanium Dioxide Oxygen
Sensor at all four positions, this is a very delicate five volt sensor that is beyond the
scope of this paper.
 Conventional [HEGO] Oxygen Sensors
Bank 1 – Sensor 1 [O2S11]
Bank 2 – Sensor 1 [O2S21]
Voltage output of upstream [first] Exhaust Oxygen sensor. Varies between .2v
and .8v normally. Used mainly for fueling control, air/fuel ratio and emissions
monitoring.
 Universal [UHEGO] Oxygen Sensors
Bank 1 – Sensor 1 [WO2S11]
Bank 2 – Sensor 1 [WO2S21]
ECM monitors the current, positive or negative, needed to drive the operation of
the sensor in response to the exhaust oxygen content, and reports that value.
Positive amps indicate a lean system and negative indicate a rich system.
Bank 1 – Sensor 1 Equivalence Ratio
Bank 2 – Sensor 1 Equivalence Ratio
This PID is of limited value to technicians, and has even less value to the novice.
This value is the commanded fuel to oxidizer ratio that the ECM wants to
achieve. In essence ‘Equivalence Ratio’ is the reciprocal of the air/fuel ratio.
Revision 2
©S. Petry
Indianapolis, IN
8/24/2011
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OBDII and Emissions Testing Pg 1 of 1 http://www.obdii.com
OBDII and Emissions Testing
Are you up to speed on OBD II? You should be because starting in 2002, a number of states have announced
plans to change their emissions testing programs over to OBD II.
Instead of doing a tailpipe emissions check on a dynamometer, an OBD II check is a simple plug-in test that
takes only seconds. What’s more, OBD II will detect emissions problems that might not cause a vehicle to fail a
tailpipe test - which means emissions test failures under the OBD II test programs are expected to be
significantly higher.
The second-generation self-diagnostic emissions software has been required on all new vehicles sold in this
country since model year 1996, including all imports. OBD II is a powerful diagnostic tool that can give you
insight into what’s actually happening within the engine control system.
Unlike earlier OBD systems that set a DTC when a sensor circuit shorts, opens or reads out of range, OBD II is
primarily emissions-driven and will set codes anytime a vehicle’s emissions exceed the federal limit by 1.5
times.It also will set codes if there is a gross sensor failure, but some types of sensor problems won’t always
trigger a code. Consequently, the Check Engine light on an OBD II-equipped vehicle may come on when there
is no apparent driveability problem, or it may not come on even though a vehicle is experiencing a noticeable
driveability problem.
The determining factor as to whether or not the Check Engine light comes on is usually the problem’s effect on
emissions. In many instances, emissions can be held in check, despite a faulty sensor, by adjusting fuel trim. So
as long as emissions can be kept below the limit, the OBD II system may have no reason to turn on the light.
CHECK ENGINE LIGHT
The "Malfunction Indicator Lamp" (MIL), which may be labeled "Check Engine" or "Service Engine Soon" or a
symbol of an engine with the word "Check" in the middle, is supposed to alert the driver when a problem occurs.
Depending on how the system is configured and the nature of the problem, the lamp may come on and go off,
remain on continuously or flash - all of which can be very confusing to the motorist because he has no way of
knowing what the light means. Is it a serious problem or not? If the engine seems to be running okay, the
motorist may simply ignore the light. With OBD II, the Check Engine light will come on only for emissions-related
failures. A separate warning light must be used for other non-emissions problems such as low oil pressure,
charging system problems, etc.
If the light is on because of a misfire or a fuel delivery problem, and the problem does not recur after three drive
cycles (under the same driving conditions), the Check Engine light may go out. Though you might think the
vehicle has somehow healed itself, the intermittent problem may still be there waiting to trigger the light once
again when conditions are right. Whether the light goes out or remains on, a code will be set and remain in the
computer’s memory to help you diagnose the fault.
With some exceptions, the OBD II warning lamp will also go out if a problem does not recur after 40 drive
cycles. A drive cycle means starting a cold engine and driving it long enough to reach operating temperature.
The diagnostic codes that are required by law on all OBD II systems are "generic" in the sense that all vehicle
manufacturers use the same common code list and the same 16-pin diagnostic connector. Thus, a P0302
misfire code on a Nissan means the same thing on a Honda, Toyota or Mercedes-Benz. But each vehicle
manufacturer also has the freedom to add their own "enhanced" codes to provide even more detailed
information about various faults.
Enhanced codes also cover non-emission related failures that occur outside the engine control system. These
include ABS codes, HVAC codes, air bag codes and other body and electrical codes.
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The second character in an OBD II will be a zero if it’s a generic code, or a "1" if it’s a dealer enhanced code
(specific to that particular vehicle application).
The third character in the code identifies the system where the fault occurred. Numbers 1 and 2 are for fuel or
air metering problems, 3 is for ignition problems or engine misfire, 4 is for auxiliary emission controls, 5 relates
to idle speed control problems, 6 is for computer or output circuit faults, and 7 and 8 relate to transmission
problems.
Codes can be accessed and cleared using an OBDII scan tool such as AutoTap.
MISFIRE DETECTION
If an emissions problem is being caused by engine misfire, the OBD II light will flash as the misfire is occurring.
But the light will not come on the first time a misfire problem is detected. It will come on only if the misfire
continues during a second drive cycle and will set a P0300 series code.
A P0300 code would indicate a random misfire (probably due to a vacuum leak, open EGR valve, etc.). If the
last digit is a number other than zero, it corresponds to the cylinder number that is misfiring. A P0302 code, for
example, would tell you cylinder number two is misfiring. Causes here would be anything that might affect only a
single cylinder such as a fouled spark plug, a bad coil in a coil-on-plug ignition system or distributorless ignition
system with individual coils, a clogged or dead fuel injector, a leaky valve or head gasket.
The OBD II system detects a misfire on most vehicles by monitoring variations in the speed of the crankshaft
through the crankshaft position sensor. A single misfire will cause a subtle change in the speed of the crank.
OBD II tracks each and every misfire, counting them up and averaging them over time to determine if the rate of
misfire is abnormal and high enough to cause the vehicle to exceed the federal emissions limit. If this happens
on two consecutive trips, the Check Engine light will come on and flash to alert the driver when the misfire
problem is occurring.
Misfire detection is a continuous monitor, meaning it is active any time the engine is running. So too is the fuel
system monitor that detects problems in fuel delivery and the air/fuel mixture, and something called the
"comprehensive monitor" that looks for gross faults in the sensors and engine control systems. These monitors
are always ready and do not require any special operating conditions.
Other OBD II monitors are only active during certain times. These are the "non-continuous" monitors and include
the catalytic converter efficiency monitor, the evaporative system monitor that detects fuel vapor leaks in the fuel
system, the EGR system monitors, the secondary air system monitor (if the vehicle has such a system), and the
oxygen sensor monitors.On some 2000 and newer vehicles, OBD II also has a thermostat monitor to keep an
eye on the operation of this key component. The thermostat monitor will be required on all vehicles by 2002. On
some 2002 model-year vehicles, there also is a new PCV system monitor, which will be required on all vehicles
by 2004.
The catalytic converter monitor keeps an eye on converter efficiency by comparing the outputs from the
upstream and downstream oxygen sensors. If the converter is doing its job, there should be little unburned
oxygen left in the exhaust as it exits the converter. This should cause the downstream O2 sensor to flatline at a
relatively fixed voltage level near maximum output.
If the downstream O2 sensor reading is fluctuating from high to low like the front sensor, it means the converter
is not functioning.The Check Engine light will come on if the difference in O2 sensor readings indicates
hydrocarbon (HC) readings have increased to a level that is 1.5 times the federal limit. For 1996 and newer
vehicles that meet federal Low Emission Vehicles (LEV) requirements, the limit allows only 0.225 grams per
mile (gpm) of HC - which is almost nothing. Converter efficiency drops from 99 percent when it is new to around
96 percent after a few thousand miles. After that, any further drop in efficiency may be enough to turn on the
Check Engine light. We’re talking about a very sensitive diagnostic monitor.
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The EVAP system monitor checks for fuel vapor leaks by performing either a pressure or vacuum test on the
fuel system. For 1996 through 1999 vehicles, the federal standard allows leaks up to the equivalent of a hole
.040 inches in diameter in a fuel vapor hose or filler cap. For 2000 and newer vehicles, the leakage rate has
been reduced to the equivalent of a .020 in. diameter hole, which is almost invisible to the naked eye but can be
detected by the OBD II system. Finding these kinds of leaks can be very challenging.
READINESS FLAGS
An essential part of the OBD II system are the "readiness flags" that indicate when a particular monitor is active
and has taken a look at the system it is supposed to keep watch over. The misfire detection, fuel system and
continuous system monitors are active and ready all the time, but the non-continuous monitors require a certain
series of operating conditions before they will set - and you can’t do a complete OBD II test unless all of the
monitors are ready.
To set the converter monitor, for example, the vehicle may have to be driven a certain distance at a variety of
different speeds. The requirements for the various monitors can vary considerably from one vehicle
manufacturer to another, so there is no "universal" drive cycle that will guarantee all the monitors will be set and
ready.
As a general rule, doing some stop-and-go driving around town at speeds up to about 30 mph followed by five to
seven minutes of 55 mph plus highway speed driving will usually set most or all of the monitors (the converter
and EVAP system readiness monitors are the hardest ones to set). So if you’re checking the OBD II system and
find a particular monitor is not ready, it may be necessary to test drive the vehicle to set all the monitors.
The Environmental Protection Agency (EPA) realized this shortcoming in current generation OBD II systems.
So, when it created the rules for states that want to implement OBD II testing in place of tailpipe dyno testing, it
allows up to two readiness flags to not be set prior to taking an OBD II test on 1996 to 2000 vehicles, and one
readiness flag not to be set on 2001 and newer vehicles. You can use the AutoTap OBDII scantool to check that
your readiness flags are set before having your vehicle emissions-tested. This can save you the aggrevation of
being sent off to drive around and come back later.
Some import vehicles have known readiness issues. Many 1996-’98 Mitsubishi vehicles will have monitors that
read "not ready" because setting the monitors requires very specific drive cycles (which can be found in their
service information). Even so, these vehicles can be scanned for codes and the MIL light without regard to
readiness status.On 1996 Subarus, turning the key off will clear all the readiness flags. The same thing happens
on 1996 Volvo 850 Turbos. This means the vehicle has to be driven to reset all the readiness flags. On 1997
Toyota Tercel and Paseo models, the readiness flag for the EVAP monitor will never set, and no dealer fix is yet
available. Other vehicles that often have a "not ready" condition for the EVAP and catalytic converter monitors
include 1996-’98 Volvos, 1996-’98 Saabs, and 1996-’97 Nissan 2.0L 200SX models.
OBD II TEST
An official OBD II emissions test consists of three parts:
1. An inspector checks to see if the MIL light comes on when the key is turned on. If the light does not
come on, the vehicle fails the bulb check.
2. A scanner similar to AutoTap is plugged into the diagnostic link connector (DLC), and the system is
checked for monitor readiness. If more than the allowed number of monitors are not ready, the vehicle is
rejected and asked to come back later after it has been driven sufficiently to set the readiness flags. The
scanner also checks the status of the MIL light (is it on or off?), and downloads any fault codes that may
be present.If the MIL light is on and there are any OBD II codes present, the vehicle fails the test and
must be repaired. The vehicle also fails if the DLC is missing, has been tampered with or fails to provide
any data.
3. As a final system check, the scanner is used to command the MIL lamp on to verify it is taking
commands from the onboard computer. If the OBD II light is on, or a vehicle has failed an OBD II
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emissions test, your first job is to verify the problem. That means plugging into the OBD II system,
pulling out any stored codes and looking at any system data that might help you nail down what’s
causing the problem. Long-term fuel trim data can provide some useful insight into what’s going on with
the fuel mixture. If long-term fuel trim is at maximum, or you see a big difference in the numbers for the
right and left banks of a V6 or V8 engine, it would tell you the engine control system is trying to
compensate for a fuel mixture problem (possibly an air leak, dirty injectors, leaky EGR valve, etc.).
OBD II also provides "snap shot" or "freeze frame" data, which can help you identify and diagnose intermittent
problems. When a fault occurs, OBD II logs a code and records all related sensor values at that moment for
later analysis.
Once you’ve pinpointed the problem and hopefully replaced the faulty component, the final step is to verify that
the repair solved the problem and that the OBD II light remains off. This will usually require a short test drive to
reset all the readiness monitors and run the OBD II diagnostic checks.
OBD II TOOLS & EQUIPMENT
You can’t work on OBD II systems without some type of OBD II-compliant scanner. The AutoTap OBDII Scan
Tool is available in both PC/laptop versions and Palm PDA versions. The computing power and display of a PC
or Palm gives AutoTap a much broader range of features than the older style hand-held scantools.
The OBDII Home Page
http://www.obdii.com
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Gary Stamberger – Training Director
Car-Sound/Magnaflow Performance Exhaust
This month we take the discussion of Oxygen Sensors to yet another level. In recent discussions we talked about the role these sensors played in
closed loop fuel control. What exactly does that mean, “Closed loop fuel control”, and what role does it play in maintaining a good working
converter?
When a vehicle is started cold there is a warm up period which is referred to as, “Open loop”. It’s during this time period that the engine is polluting
the most. Consequently, getting to closed loop fuel control is a top priority. The PCM has an internal clock that restarts on each start-up and it knows,
based mainly on temperature, how long before all components are operating and it is ready to enter closed loop. To this end, many elements have been
added to the systems. Oxygen sensors have built in heaters to speed the warm up process. The PCM can detect when the engine is taking too long to
come up to temperature and will set a code P0125, “Insufficient temperature for closed loop fuel control” which typically means the thermostat is
stuck open.
Once the conditions are met and the PCM gains fuel control the goal then becomes maintaining it. The oxygen sensor is referred to as a, “Voltage
Generator” and reports the content of oxygen in the exhaust stream to the PCM ranging between 100mv (Millivolts) and 900mv. When the oxygen
content is high, (Voltage is low, near 100mv) the PCM sees this as a lean condition and its response is to add fuel. When the sensor reports back that
there is little oxygen in the exhaust stream (high voltage, near 900mv), a rich condition is sensed and the PCM pulls fuel away. A technician can
monitor this data on a scan tool as, “Short Term Fuel Trim” or STFT. A positive percentage indicates the computer is adding fuel while a negative
number says it is taking fuel away. If the PCM is in fuel control, monitoring the direct relationship between O2 and STFT scan data will confirm it.
The next step then is to look at Long Term Fuel Trim (LTFT) percentages. These numbers give us a history of what the PCM has been doing with fuel
trim over the long haul. As with STFT, positive percentages tell us the tendency is to be adding fuel (compensating for a lean condition) while
negative numbers indicate the PCM is pulling fuel back, (Overcoming a rich condition). If either of these conditions exists for a prolonged period of
time and the LTFT percentages exceed the PCM’s parameters a fuel trim code will set (P0170-P0175) and Check Engine light illuminated. The
example below shows us that although the PCM appears to be in fuel control there is evidence that it has been adding fuel over time.
Our concern when looking at fuel trim is what it may be telling us about engine efficiency and whether the computer has been compensating for other
fuel related problems. If the engine has been over-fueling the question is…WHY? A leaking fuel injector, fuel pressure regulator, lazy O2, or bad
Mass Air Flow (MAF) would be some of the considerations. The same issue exists if it’s too lean. Here an air leak, clogged injectors or fuel filter, or
miscalculated air flow could be the cause. Any Fuel Trim condition that persists will eventually take its toll on the catalytic converter and must be
addressed by the repair technician before installing a new one.
Cleaning up the environment…one converter at a time
Gary
INTERPRETING FUEL TRIM DATA
Bulletin TB-80010
May, 2009
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Magnaflow Exhaust Products
In the first part of this OBD II Code Diagnosis series I stated that we would discuss the principles of OBD II codes and
breakdown each character that defines them. For a generic discussion of OBD I’ll refer you to TB-80016 and 80017. We archive all
of our bulletins and they can be found on our website at www.maganaflow.com. Look for Tech Bulletins under Tech Support. For
this series I would like to stay on a more specific path.
In our first two parts we took a very common Ford EGR code and broke down the diagnosis. I chose this code not only for its
commonality but also because this EGR system uses several components, each one playing a major role in the vehicles ability to
reduce NOx. Although the PCM has the ability to set several different and distinct codes for each component (9 generic and 10
specific) the interrelation of the components cannot be ignored. As we saw in our example, one of the possible causes for the P0401
code was mechanical and had nothing to do with the malfunction of any one component.
Another common issue in Code Diagnostics sometimes overlooked is that of retrieving codes in both OBD II Generic and Enhanced
or Manufacture Specific mode. Depending on the tool being used, the enhanced option may not be available (i.e. Code Reader only).
Using generic mode requires less input therefore is faster and in most cases will get the technician to where he wants to be. The
downside is that it is a generic code and therefore in many cases the repair information will not be specific to that vehicle.
The obvious upside then to using Enhanced Mode, is that the diagnostic information will be specific to that vehicle or at least that
manufacturer. The description and operation will give you a better idea of what the PCM is looking for and the subsequent testing
should lead you to the proper diagnosis the first time.
Example: 2005 Altima, 2.5L with an illuminated MIL. The OBD II code was P0140, O2 Circuit B1S2 No Activity Detected. A quick
glance at the data stream showed that under the proper test conditions the sensor displayed activity. At this point we might determine
that it is an intermittent problem, clear the code and send the customer on their way. However a look at Enhanced codes revealed a
P1147, O2 B1S2 Maximum Voltage not Obtained. A closer look at data stream showed that the sensor was not reaching a specific
maximum voltage of .78v. This specific information was not available when processing the P0140 code.
The key to any diagnostic situation is to always follow a pattern for each problem we face and code diagnostics is no different. Yes…
each manufacture has common problems and knowing where to find that information is valuable but sometimes even the “silver
bullet” can be a dud! Whether it is a no start, misfire, won’t idle, MIL illuminated or any number of issues, having a plan is by far the
best plan. “Shot Gun” diagnosis will on occasion allow us to hit the illusive homerun but more often than not we spend a whole day
repairing a component only to go home with that empty feeling in our stomachs, knowing the same problem will reoccur in the
morning.
Diagnostics is an art and getting good at it can be a great confidence booster, however these vehicles are changing constantly and
there is no time to rest. As I say when closing all my classes:
THE RULES ARE ALWAYS CHANGING
TECHNOLOGY KEEPS MOVING FORWARD
EDUCATION IS A CONTINUAL PROCESS
Cleaning up the environment…one converter at a time
Gary
OBD II Code Diagnosis Part III
Bulletin TB-80035
September, 2011
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ScanMaster-ELM
What is OBD-II?
OBD-II stands for On-Board Diagnostics second (II) generation, a computer-based system
built into all model year (MY) 1996 in USA and newer light-duty cars and trucks. OBD-II
monitors the performance of some of the engines' major components, including individual
emission controls. The system provides owners with an early warning of malfunctions by way
of a dashboard "Check Engine" light (also known as a Malfunction Indicator Light or MIL, for
short). By giving vehicle owners this early warning, OBD-II protects not only the
environment but also consumers, identifying minor problems before they become major
repair bills.
EOBD - European On-Board Diagnostic
EOBD is a standard that is issued by the European Community. The main goal with the
standard is to give the authorities a tool to control the exhaust emission from vehicles. The
EOBD standard has been implemented in petrol cars throughout the European Union from
01.01.2001 (EU directive 98/96/EC). For LPG and Diesel vehicles the implementation of
applicable regulations is scheduled to take place before 2005. The EOBD standard includes
five different communication protocols: ISO 9141-2, ISO 14230-4(KWP2000), SAE J1850
VPW, SAE J1850 PWM and ISO 15765-4 CAN.
If the car supports EOBD you have the possibilities to read out stored information from the
ECU in the car, including:
€ Read fault codes
€ Erase fault codes
€ Read freeze frame data
€ Get real-time data (displayed as numbers or graphs)
€ Get monitoring results from oxygen sensors
€ Get result from readiness test
To read out the information you require an OBD-II/EOBD diagnostic tool such as the
ScanMaster software together with an approbiate interface for the connection between the
cars diagnostic connector and the computer or notbook.
How do I know the OBD system is working correctly?
When you turn on the ignition, the "Service Engine Soon" or "Check Engine" light should
flash briefly, indicating that the OBD system is ready to scan your vehicle for any
malfunctions. After this brief flash, the light should stay off while you drive as long as no
problems are detected. If so, you'll be glad to know that your vehicle is equipped with an
early warning system that could save you time, money, and fuel in addition to helping
protect the environment!
www.wgsoft.de
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ScanMaster-ELM
Which OBD-II protocol is supported by vehicle?
All cars and light trucks built for sale in the United States after 1996 are required to be OBD-
II compliant. The European Union adopted a similar law in 2000 for gasoline-powered
vehicles, and in 2003 for cars with diesel engines.
An OBD-II compliant vehicle can use any of the five communication protocols: J1850 PWM
and VPW, ISO9141, ISO14230 (also known as Keyword Protocol 2000), and more recently,
CAN (ISO15765/SAE J2480). Car manufacturers were not allowed to use CAN until model
year 2003.
As a general rule, you can determine which protocol your vehicle is using by looking at the
pinout of the DLC:
The following table explains how to determine the protocol:
Pin 2 Pin 6 Pin 7 Pin 10 Pin 14 Pin 15* Standard
J1850
Bus+
CAN High
ISO 9141-2
K Line and
ISO/DIS
14230-4
J1850 Bus CAN Low
ISO 9141-2
L Line and
ISO/DIS
14230-4
must have - - must have - - J1850 PWM
must have - - - - - J1850 VPW
- - must have - - may have ISO9141/14230
- must have - - must have - CAN
The connector should have: Pin 4 - Chassis Ground, Pin 5 - Signal Ground, Pin 16 - Battery
power
www.wgsoft.de
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ScanMaster-ELM
This means that:
Protocol The connector must have pins
PWM 2, 4 and/or 5, 10, and 16
VPW 2, 4 and/or 5, and 16, but not 10.
ISO 4 and/or 5, 7, and 16. Pin 15 *may or may not be present.
CAN 4 and/or 5, 6, 14 and 16
*For ISO communications, pin 15 (L-line) is not always required. Pin 15 was used on earlier
ISO/KWP2000 cars to "wake-up" the ECU before communication could begin on pin 7 (K-
Line). Later cars tend to communicate using only pin 7 (K-Line).
Because of the different protocol a car might have it is recommended to use an interface
which supports all protocols as all modern interfaces do.
www.wgsoft.de
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ScanMaster-ELM
Diagnostic Link Connector (DLC) Mapping Diagram Explanation
The mapping diagram of DLC locations contains a divided instrument panel (IP) with
numbered areas. Each numbered area represents specific sections of the IP where
manufacturers may have located DLCs. This document briefly clarifies the numbered
locations on the mapping diagram. We will use this mapping diagram to catalog
manufacturer responses to the recent 208 letter requesting OBD DLC locations for 96MY and
future vehicles. Areas 1-3 fall within the preferred DLC location while the remaining areas, 4-
8, fall into the allowable DLC location according to EPA requirements. Areas 4-8 require that
manufacturers label the vehicle in the preferred location to notify parties of the alternate
connector location.
Preferred Location(s)
Location #1: This location represents a DLC positioned on the underside of the IP directly
under the steering column (or approximately 150mm left or right of the steering column).
Visualizing the underside of an IP divided into three equal parts from inside the passenger
compartment, this represents the center section.
Location #2: This location represents a DLC positioned on the underside of the IP between
the steering column and the drivers side passenger door. Visualizing the underside of an IP
divided into three equal parts from inside the passenger compartment, this represents the
left section.
Location #3: This location represents a DLC positioned on the underside of the IP between
the steering column and the center console. Visualizing the underside of an IP divided into
three equal parts from inside the passenger compartment, this represents the right section.
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ScanMaster-ELM
Allowable Location(s)
Location #4: This location represents a DLC positioned on the upper part of the IP between
the steering column and the center console (but not on the center console, see location #6).
Location #5: This location represents a DLC positioned on the upper part of the IP between
the steering column and the driver side, passenger door.
Location #6: This location represents a DLC positioned on the vertical section of the center
console and left of the vehicle center line.
Location #7: This location represents a DLC positioned 300 mm right of the vehicle
centerline either on the vertical section of the center console or on the passenger side of the
vehicle.
Location #8: This location represents a DLC positioned on the horizontal section of the
center console either left or right of the vehicle center line. This does not include the
horizontal section of the center console that extends into the rear passenger area (see
location #9).
Location #9: This location, not shown, represents any DLC positioned in an area other than
those mentioned above (e.g., in the rear passenger area on the driver side armrest).
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ScanMaster-ELM
OBD-II Diagnostic Protocol
The diagnostic protocol for OBD-II is SAE J1979. A diagnostic request or response message
has a maximum of seven data bytes. The first byte following the header is the test mode. It
is also called the service identifier (SID or PID). The following bytes vary depending on the
specific test mode.
There are nine diagnostic test modes:
Mode $01 – Request Current Powertrain Diagnostic Data - This service gives access
to current emission-related data values, including analogue inputs and outputs, digital inputs
and outputs and system status information.
Mode $02 – Request Powertrain Freeze Frame Data - This service gives access to
current emission-related data values in a freeze frame. A freeze frame consists of data
values stored at a specific event; such as an engine malfunction of some kind.
Mode $03 – Request Emission-Related Powertrain Diagnostic Trouble Codes - The
purpose of this service is to enable the external test equipment to obtain “confirmed”
emission-related DTCs.
Mode $04 – Clear/Reset Emission-Related Diagnostic Information - The purpose of
this service is to provide a means for the external test equipment to command ECUs to clear
all emission-related diagnostic information. This includes:
€ Number of diagnostic trouble codes
€ Diagnostic trouble codes
€ Trouble codes for Freeze Frame data
€ Freeze Frame data
€ O2 test data
€ Status of system monitor tests
€ On-board monitor test results
€ Travelled distance with activated MIL
€ Number of warm startups since DTC clear
€ Travelled distance since DTC clear
€ Engine runtime (minutes) with MIL activated
€ Time since DTC clear
€ as well as learned adaptive values of the injection system.
Other manufacturer specific clear/reset actions might be possible.
Mode $05 – Request Oxygen Sensor Monitoring Test Results - The purpose of this
service is to allow access to the on-board oxygen sensors monitoring test results.
Mode $06 – Request On-Board Monitoring Test Results for Non- Continuously
Monitored Systems - This service gives access to the results for on-board diagnostic
monitoring tests of specific components/systems that are not continuously monitored.
Examples of this are catalyst monitoring and the evaporative system monitoring.
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ScanMaster-ELM
Mode $07 – Request On-Board Monitoring Test Results for Continuously
Monitored Systems - Through this service, the external test equipment, can obtain test
results for emission-related Powertrain components/systems that are continuously monitored
during normal driving conditions.
Mode $08 – Request Control of On-Board System, Test or Component - This service
enables external test equipment to control the operation of an on-board system, test or
component.
Mode $09 – Request Vehicle Information - This service gives access to vehicle specific
vehicle information such as Vehicle Identification Number (VIN) and Calibration IDs.
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Reading Performance Information Data (PID)
Posted by Alex (Im) E. on 01 February 2013 12:11 AM
PIDS are the serial data that can be accessed from the vehicle computer using a scan tool. PIDS include:
 Status of the OBD II System Component Monitors
(Ready or Complete, or Not Ready or Incomplete)
 Live Sensor Data
(Oxygen sensor rich/lean indication, coolant temperature, MAP value, TPS value, vehicle speed, mass
air flow, ambient temperature, engine rpm, etc.)
 Status of Switches or Devices
(cruise control on/off. brake pedal switch on/off. TCC engaged/disengaged, etc.)
 Long and Short Term Fuel Trim, O2 sensor cross counts, injector duration.
DIAGNOSTIC VALUE
PIDS provide valuable diagnostic information when checking the operation or status of various sensors, circuits
and switches in the vehicle's engine management system.
For example, if the MIL lamp is on and you find an oxygen sensor code, you can call up the oxygen sensor
PIDS on your scan tool display to see what the oxygen sensor is telling the PCM.
You can also compare PIDS to see how one component may be affecting another.
For example, when you suddenly open the throttle on an idling engine, rpm should increase, the TPS reading
should change and the MAP sensor value should drop.
PIDS can also be compared using a "graphing multimeter" or on a scope that converts the voltage values to
waveforms.
Comparing the waveforms of several related sensors can help you find faults that might otherwise be
impossible to detect.
SCAN TOOL PID CAPABILITY
Different scan tools have different capabilities to display PIDS.
The OEM scan tools used by new car dealers are capable of displaying every possible PID value that is built
into the engine management system.
Most general purpose aftermarket scan tools do not contain the software that allows them to match the OEM
scan tools in every respect -- but for most applications they can display all the important PIDS.
The trouble is you never know what PIDS are missing until you go looking for one and find it isn't there.
Bummer.
That's why many professional technicians own multiple scan tools: an aftermarket general purpose scan tool,
and one or more OEM scan tools for the makes they most frequently work on.
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Scan tools like TOAD support various PIDS including live data values, the status of switches and other
devices, the readiness status of various OBD II monitors, and other test results.
Live data provides real-time measurements of system inputs.
Statuses tell you if a switch, relay or other device is ON/OFF or has been commanded ON or OFF.
Readiness monitors tell you if the monitors have completed or not.
Test results are measured by the PCM and compared against preprogrammed pass/fail values in teh PCM's
memory.
LIVE DATA:
 Air Flow Rate From MAF -- The airflow rate as measured by the mass air flow sensor.
 Absolute Throttle Position -- The absolute throttle position (not the relative or learned) throttle
position. Usually above 0% at idle and less than 100% at full throttle.
 Calculated Load Value -- Indicates a percentage of peak available torque. Reaches 100% at wide
open throttle at any altitude or RPM for both naturally aspirated and boosted engines.
 Engine Coolant Temperature -- Engine coolant temperature as read by the engine coolant
temperature sensor. This value should be compared to the actual coolant temperature to see if they
match.
You can use an infrared thermometer or other thermometer to measure the temperature of the coolant
at the thermostat outlet. If the actual temperature and displayed temperature do not match, it would tell
you the coolant sensor is not reading correctly.
 Engine RPM -- The current engine speed in revolutions per minute (RPM).
 Fuel Rail Pressure -- Pressure in the fuel rail when the reading is referenced to atmosphere (gauge
pressure).
 Ignition Timing Advance -- Degrees of ignition timing (spark) advance for #1 cylinder (not including
mechanical advance). Intake Manifold
 Pressure -- Pressure in the intake manifold derived from a Manifold Absolute Pressure (MAP) sensor.
 Long Term Fuel Trim (LTFT) -- The correction factor (percentage) being used by the fuel control
system in both open and closed loop modes of operation. LTFT should typically be within plus or minus
five. Positive LTFT numbers indicate the PCM is adding more fuel to compensate for a lean fuel
condition.
Negative LTFT numbers mean the PCM is delivering less fuel to compensate for a rich fuel condition. If
the LTFT is higher than 10 either way, it may indicate a problem.
 Short Term Fuel Trim (STFT) -- The correction factor being used in closed loop by the PCM to
maintain a balanced fuel mixture. If the fuel system is open loop, 0% correction should be reported. As
with LTFT, the number should usually be plus or minus five. If greater than 10, it indicates a fuel
mixture problem.
 O2 Sensor Output Voltage -- The actual voltage being generated by the oxygen sensor (should be 0.1
to 1.0 volts for a conventional zirconia O2 sensor).
For wide-band O2 sensors and linear O2 sensors, the value may be higher, or it may be converted to a
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zero to one volt scale.
There may be multiple O2 sensor PIDS depending on homw many sensors the engien has (Bank1
sensor 1, Bank2 Sensor 1, etc.).
 Time Since Engine Start -- Shows the time the engine has been running since it was last started.
Vehicle Speed -- Displays vehicle road speed as read by the vehicle speed sensor (VSS).
 Absolute Load Value -- This is the normalized value of air mass per intake stroke displayed as a
percent.
 Absolute Throttle Position -- The absolute throttle position (not the relative or learned) throttle
position. Usually above 0% at idle and less than 100% at full throttle.
 Accelerator Pedal Position -- The absolute pedal position (not the relative or learned) pedal position.
Usually above 0% at idle and less than 100% at full throttle.
 Ambient Air Temperature -- The ambient air temperature as ready by the air temperature sensor. This
value can be compared to the temperature reading by another thermometer to see if the values match.
If they do not, the air temperature sensor is not reading accurately.
NOTE: the temperature reading will depend on the location of the sensor. If the sensor is located under
the hood, it may read higher than the outside temperatrue when the vehicle is not moving becuase of
engine heat.
 Barometric Pressure -- Barometric pressure as determined by a barometric pressure (BARO) sensor.
Note some weather services report barometric pressure adjusted to sea level. In these cases, the
reported value may not match the displayed value.
 Catalyst Temp -- The temperature inside the catalytic converter.
 Commanded EGR -- Tells you what the PCM is commanding the EGR valve to do.
The percentage vlue should be 0% when EGR is commanded off (at idle), 100% when EGR is
commanded on (typically when cruising under light load), and between 0% and 100% is the EGR
solenoid is duty cycled on and off by the PCM (depending on vehicle speed, engine load and
temperature).
 Commanded Equivalence Ratio -- Fuel systems that use conventional oxygen sensor displays the
commanded open loop equivalence ratio while the system is in open loop. Should report 100% when in
closed loop fuel.
To obtain the actual air/fuel ratio being commanded, multiply the stoichiometric A/F ratio by the
equivalence ratio. For example, gasoline, stoichiometric is 14.64:1 ratio.
If the fuel control system was command an equivalence ratio of 0.95, the commanded A/F ratio to the
engine would be 14.64 * 0.95 = 13.9 A/F.
 Commanded Evaporative Purge -- This value should read 0% when no purge is commanded and
100% at the maximum commanded purge position/flow.
 Commanded Throttle Actuator -- This value should be 0% when the throttle is commanded closed
and 100% when the throttle is commanded open.
 Control Module Voltage -- Power input to the control module. Normally, this should show battery
voltage minus any voltage drop between the battery and the control module (which should be less than
a few tenths of a volt).
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Distance Since DTCs Cleared -- How many miles the vehicle has been driven since any DTCs were
cleared with a scan tool. Distance
 Traveled While MIL On -- Tells you how many miles the vehicle has been driven with the MIL light on.
Also tells you
how long the driver has been ignoring the light!
 EGR Error -- Calculated error as percent of actual commanded EGR. Negative percent is less than
commanded and positive is more than commanded. The greater the value, the more likely the EGR
valve is sticking.
 EVAP Purge -- This value is displayed as a percentage and is normalized for all types of EVAP
systems. When EVAP purge is commanded off, the value should be o%, and 100% when it is
commanded on.
This is an important value o check if the engine has lower than normal LTFT and STFT fuel trim
numbers (indicating a rich fuel condition). The purge valve may be leaking vapor into the intake
manifold.
To eliminate the purge valve as a possible source of fuel vapor, pinch off the purge vapor hose, run the
engine and recheck the STFT number. If it is back to normal, the purse valve is leaking.
 EVAP System Vapor Pressure -- Evaporative system vapor pressure normally obtained from a sensor
located in the fuel tank.
 Fuel Level Input -- Indicates the nominal fuel tank liquid fill capacity as a percent of maximum.
 Fuel Rail Pressure -- Indicates the fuel rail pressure at the engine referenced to atmosphere (gauge
pressure).
 Fuel Rail Pressure Rel Manifold -- The fuel rail pressure referenced to the manifold vacuum (relative
pressure).
 Intake Air Temperature -- The temperature of the air in the intake manifold as read by the intake
manifold air temperature sensor. This should be the same as ambient temperature in a cold engine that
has not been started, and should be higher than ambient tempertarue if teh engine is warm and has
been running.
 Minutes Run with MIL On -- Accumulated minutes of engine run time while the MIL light is on.
 O2 Sensor Wide Range mA -- Milliamp current for linear or wide-ratio oxygen sensors.
 O2 Sensor Wide Range V -- Voltage for linear or wide-ratio oxygen sensors.
 Relative Throttle Position -- Relative or learned throttle position.
 Time Since DTCs Cleared -- Accumulated time since DTCs where cleared with a scan tool.
 Warm-ups Since DTCs Cleared -- Number of warm-up cycles since all DTCs were cleared with a scan
tool. A warm-up is defined as the coolant temperature rising by at least 22°C (40°F) and the engine
temperature reaches at a minimum 70°C (160°F), or 60°C (140°F) for diesel engines.
TROUBLE CODES AND FREEZE FRAME DATA
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Code readers and scan tools will also display Stored Diagnostic Trouble Codes (DTCs), usually in numeric
order.
Many scan tools can also display Pending Trouble Codes.
These are codes that indicate a fault has been detected, but that the fault has not yet repeated.
If the fault repeats under similar driving conditions, it will usually cause the Pending Code to become a Stored
Code and turn on the MIL light.
Many scan tools can also display Freeze Frame data.
These are PIDS that are captured when a fault occurs so you can refer to them later when diagnosing the
problem.
Freeze frame data typically includes related sensor values at the time the fault occurred.
STATUS AND READINESS MONITORS
OBD II requires the following status and readiness monitors:
 Fuel System 1 Status
 Fuel System 2 Status
 Secondary Air Status
 Auxiliary Input Status
 Misfire Monitor Status
 Fuel System Status
 Comprehensive Component Monitoring Status
 Catalyst Monitoring Status
 Heated Catalyst Monitoring Status
 Evaporative System Monitoring Status
 Secondary Air System Monitoring Status
 A/C System Refrigerant Monitoring Status
 Oxygen Sensor Monitoring Status
 Oxygen Sensor Heater Monitoring Status
 EGR System Monitoring Status
 ECU Oxygen Sensor Test Results
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Shopping Tips for Selecting an OBDII compatible scantool
There are a growing number of scantools compatible with 1996 and newer vehicles with a wide
variety of features. With prices ranging from $250 to $2500 anyone looking for a scantool needs
to do a little homework to find a tool that best fits their needs.
Will it work on your vehicle?
First and foremost, the tool you purchase must support the vehicles you anticipate working on.
Although it's true that OBDII is a standard, there are five different types of hardware
communications used by OBDII vehicles. Some tools support all five and some are manufacturer
specific.
Supported parameters
Not all scantools are equal. In fact, some aren't even close. As part of the OBDII standard, the
US Environmental Protection Agency mandated that a basic set of emissions related readings be
supported on all OBDII vehicles. The SAE specification J1979 defines these legislated
parameters. Many low-end tools only support these emissions related readings, giving you
access to only a dozen or so truly useful parameters. While these give you some basic vehicle
information, they are just a small set of the vehicle information available through the OBDII port.
Is it upgradeable?
Each year vehicle manufacturers release new models and revise existing models. For a scantool
to fully support the new vehicles, it must typically be updated. Professional quality scantools are
updateable, although often at a price of $500 or more per update. Most lower end handheld
scantools are not updateable. Check what updates will cost before committing to a tool.
Built in help
For anyone working on his or her own vehicle, the Factory Service Manual is a must-have. But
the scantool itself may be able to provide some of that necessary information. When a DTC is
set, does the tool display the DTC number or give the full definition? A tool that displays the full
definition will save a lot of time and frustration. Does the tool offer any information on typical
readings to explain what the reading is? A simple sentence or two of explanation can save a lot
of trips back and forth to the shop manual.
Data logging or storage
A sure way to park your car in a ditch is to try and watch a scantool display while doing a
roadtest. A tool that stores data to allow safe viewing back at the garage is a must. Be certain
that the tool you buy has this capability.
[ OBD-II Home ]
© 2011 B&B Electronics
The OBD-II Home Page is hosted by
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How Car Diagnostic Software and Tools Work
February 17, 2012
Most car diagnostic software is based on reading data from your vehicle's OBD-II (onboard
diagnostic) system. Learn how to use a car diagnostic tool.
Car diagnostic software helps keep your vehicle running smoothly. This software is built into all cars
made after 1996, and it is included in many earlier cars as well. The latest technology is called OBD-
II, which stands for on board diagnostic system. The OBD-II is incredibly useful to mechanics and
other people curious about the status of their vehicle when something seems to go wrong.
Positioning of the Software
The OBD-II system in your vehicle has sensors and ports in various parts of the car. There is one
underneath the dash of most cars, and many vehicles also have a port under to the driver's seat.
There are other sensors and activation centers spread throughout the vehicle in order to monitor the
activity of various parts of the car. Essentially, the software is located all throughout the vehicle.
Function of the Software
The OBD-II monitors the proper functioning of your vehicle. It not only controls certain engine
functions through the on board computer, it also keeps a record of all of the things that happen to
your car as you drive it, good and bad. This information can be used later by mechanics, who
download a series of diagnostic codes from the OBD-II port. These codes explain what is going on
with the vehicle, and are the basis for the diagnosis of your problem and how to fix it when the check
engine light comes on or if you experience other problems.
Process
The software that measures the diagnostics of your car takes regular readings of different systems in
the car. This is primarily centered on the engine, but the OBD-II includes sensors for the chassis,
frame and other parts of the car too. At each reading, the software records a particular acronym or
code that represents the functionality of that system. This information is stored within the OBD-II
system and can be retrieved by attaching a computer to the port. The mechanic then downloads the
codes and translates them to determine exactly what was going on at each point of inspection. This
helps to calculate when and how damage occurred to a part of your car.
How to Use a Car Diagnostic Tool
An auto scan tool can be used to read the diagnostic software. Also called a car code reader or an
OBD-II scanner, this tool is a useful way to determine the issues with your car without having to take
it in to a dealership or a mechanic for an expensive analysis.
You'll need the following materials in order to take a diagnostic reading of your car:
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 A Laptop, iPhone or iPod Touch
 Jack cables and a port connector
 A scanner or car code reader
 A breakdown of codes and acronyms for your vehicle
Install the Computer Software
Computer scanner systems require that you connect the scanner to a computer. An iPhone or iPod
Touch will also work with devices such as the REV iPhone Car Diagnostic Tool. In order to get a
reading from the car diagnostic device, install the software that comes with the scanner system. This
allows the computer to display the readings from the diagnostic tool.
Connect the Scanner
Find the port where you can attach the scanner. This port is often located on the dash, typically just
below the steering wheel and to one side or another. Look for a small indentation and a simple port
system. The port connector may also be underneath the driver's side of the front seat. If you're having
a hard time figuring out where to connect your scanner, check the owner's manual for your car or
consult with a professional.
Get a Reading
Follow the instructions from the scanner tool and the software on your computer to take a reading of
the car diagnostic device. This will help you to determine exactly what the problem is by sending a
series of codes to your computer, which will be displayed.
Translate the Codes
Using the guidelines from the code translation sheet, figure out the problem that has caused the
malfunction or the check engine light to come on. You can then decide the best way to remedy the
problem or take your car to a mechanic.
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CHOOSING THE RIGHT SCAN TOOL
THE FOUR CRITICAL STEPS TO CHOOSING A SCAN TOOL THAT’S RIGHT FOR YOUR SHOP
BRYCE EVANS
STAFF GRAPHIC
THE FOUNDATION OF A PROPER REPAIR IS “IN THE PREPARATION,” SAYS ROBBIE BERMAN. AN
HOUR OF PREP TIME BEFORE A JOB CAN CUT OUT SUPPLEMENTS, ELIMINATE DELAYS IN PARTS
ORDERING, SHAVE CYCLE TIME AND, ULTIMATELY, IMPROVE THE FINAL PRODUCT AND THE
CUSTOMER EXPERIENCE.
THIS SHOULD BE OBVIOUS TO EVERY SHOP, BERMAN SAYS, BUT TOO OFTEN IT’S NOT.
BERMAN STARTED HIS CAREER AND HIS SHOP, ROBBIE’S AUTOMOTIVE AND COLLISION
SPECIALISTS IN WHARTON, N.J., WITH A FOCUS ON MECHANICAL REPAIR. AND HE SAYS THAT IF
THERE’S ONE THING THE COLLISION INDUSTRY CAN LEARN FROM MECHANICAL SHOPS, IT’S THE
IMPORTANCE OF DIAGNOSTICS.
“DIAGNOSTICS IS EVERYTHING, AND IT’S ONLY GROWING.” HE SAYS. “EVERY CAR COMING DOWN
THE ROAD HAS MORE AND MORE TECHNOLOGY IN IT, MORE AND MORE COMPUTER SYSTEMS.
WITHOUT THE RIGHT DIAGNOSTIC EQUIPMENT AND PROCESSES, YOU’RE NOT GOING TO BE ABLE
TO FIX VEHICLES ANYMORE.”
DIAGNOSTIC SCAN TOOLS ARE SOMETHING THAT HIS $4 MILLION, 10,000-SQUARE-FOOT COLLISION
BUSINESS HAS INVESTED IN FOR YEARS, BUT AS AN INDUSTRY, BERMAN SAYS, IT’S SOMETHING
THAT TOO MANY SHOPS ARE MISSING OUT ON.
BOB KEITH, SHOP OWNER AND DIRECTOR OF EDUCATION AND TRAINING WITH CARSTAR, AGREES.
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AND, LIKE ANY EQUIPMENT OR TOOL PURCHASE A SHOP CAN MAKE, INVESTING IN DIAGNOSTIC
SCAN TOOLS IS EXACTLY THAT—AN INVESTMENT, SOMETHING SHOPS NEED TO RESEARCH,
UNDERSTAND AND WEIGH OPTIONS ON BEFORE PURCHASING.
WHEN IT COMES TO SCAN TOOLS, THERE ARE DOZENS AND DOZENS OF OPTIONS FOR COLLISION
FACILITIES. BERMAN AND KEITH HELPED FENDERBENDER SIMPLIFY THE PURCHASING PROCESS,
OFFERING THEIR TIPS ON MATCHING YOUR BUSINESS TO THE RIGHT TOOL.
UNDERSTAND THE VALUE
KEITH LIKES TO KEEP THINGS LIGHTHEARTED IN HIS NATIONWIDE TRAINING COURSES HE RUNS
FOR CARSTAR, AND, IN DEALING WITH THE TOPIC OF TOOL AND EQUIPMENT PURCHASES, HE
LIKES TO POINT TO A ONE-PANEL COMIC.
THERE ARE A NUMBER OF VERSIONS, BUT THE GENERAL PICTURE IS THIS: A GROUP OF KNIGHTS
ARE GRABBING THEIR SWORDS AND STRAPPING ON ARMOR, GETTING READY FOR BATTLE.
BEHIND THEM STANDS A SALESMAN WITH A MACHINE GUN LOADED INTO A WAGON. THE CAPTION,
COMING FROM THE LEADER OF THE KNIGHTS, SAYS, “CAN’T THEY SEE WE DON’T HAVE TIME FOR
THIS? WE HAVE A BATTLE TO FIGHT!”
“IT CRACKS ME UP, BECAUSE YOU TALK TO A LOT OF SHOPS AROUND THE COUNTRY, AND THAT’S
THE APPROACH THEY TAKE TO TOOLS AND EQUIPMENT,” HE SAYS. “PEOPLE LOOK AT IT AS A
COST. TO AN EXTENT, IT IS, BUT YOU HAVE TO UNDERSTAND THE INVESTMENT AND THE BENEFITS
IT CAN BRING. IT’S EASY TO GET TOO CAUGHT UP IN WHAT YOU’RE DOING TO TAKE A MOMENT
AND LOOK AT THE BIGGER PICTURE OF HOW THAT INVESTMENT WILL AFFECT YOUR BUSINESS.”
EVEN BASIC, AFTERMARKET SCAN TOOLS COME WITH A FIVE-FIGURE PRICE TAG, BERMAN SAYS,
RANGING FROM $10,000–$30,000. THEN, THERE’S ANNUAL SUBSCRIPTION FEES (NORMALLY
AROUND $1,500) TO THE VEHICLE INFORMATION THE DEVICES READ.
IT’S A SUBSTANTIAL INVESTMENT FOR A COLLISION SHOP TO MAKE, BUT WITHOUT IT, WELL,
YOU’RE SIMPLY OPTING TO USE A SWORD OVER A MACHINE GUN.
“THE BENEFITS OF HAVING THE RIGHT TOOL, THE ONE THAT FITS INTO YOUR BUSINESS, FAR
OUTWIEGHS THE COST,” BERMAN SAYS. “YOU’RE INVESTING IN YOUR SHOP’S ABILITY TO
PROPERLY PERFORM WORK NOW AND IN THE FUTURE.”
THERE ARE FIVE CRITICAL STEPS TO ENSURE YOUR SHOP CHOOSES THE CORRECT SCAN TOOL.
STEP 1: IDENTIFY YOUR NEED.
WITH THE INCREASE OF IN-VEHICLE TECHNOLOGY AND COMPUTER SYSTEMS, BERMAN SAYS
EVERY SHOP NEEDS PROPER DIAGNOSTIC EQUIPMENT REGARDLESS OF THEIR WORK MIX.
HOWEVER, WHICH TOOL (OR TOOLS) YOU CHOOSE IS 100 PERCENT DETERMINED BY THAT WORK
MIX.
BOTTOM LINE: YOU NEED TO INVEST IN THE TOOLS TO FIX THE VEHICLES YOU WORK ON THE
MOST.
BERMAN SUGGESTS TAKING A HARD LOOK AT THE VEHICLES YOUR SHOP REPAIRS, RANKING
THEM FROM MOST FREQUENT TO LEAST FREQUENT. THE TOP-10 VEHICLES, HE SAYS, ARE THE
ONES YOU NEED TO FOCUS YOUR EFFORTS ON.
“IT WOULD BE GREAT TO GO TO 20 MAKES AND MODELS, OR 30, BUT IT’S UNLIKELY YOU’RE GOING
TO HAVE THE FUNDING FOR THAT,” HE SAYS. “IF YOU FOCUS ON THE ONES YOU NEED THE
MOST—AND THAT’D BE THAT TOP 10—YOU’RE GOING TO BE ABLE TO PROPERLY DIAGNOSE THE
VAST MAJORITY OF VEHICLES THAT ENTER YOUR SHOP.”
Page 26

REMEMBER, BERMAN SAYS, THAT MANY SCAN DEVICES WORK FOR MULTIPLE MAKES, MODELS
AND YEARS—MEANING THAT THE TOOL(S) YOU CHOOSE TO SUPPORT THOSE 10 VEHICLE MAKES
VERY LIKELY COULD COVER NEARLY EVERY VEHICLE YOU WORK ON.
WHICH BRINGS US TO …
STEP 2: RESEARCH TOOLS.
THIS IS WHERE THE PROCESS MAY SEEM DAUNTING, BERMAN SAYS, BUT IT DOESN’T NEED TO. IF
YOU HAVE AN UNDERSTANDING OF WHAT YOU NEED THE TOOL(S) TO DO (E.G., PROPERLY
DIAGNOSE THOSE 10 VEHICLE LINES), THEN THE SITUATION IS ALREADY SIMPLIFIED.
WHEN LOOKING AT SCAN TOOLS, BERMAN SUGGESTS FOCUSING ON THESE FIVE
CHARACTERISTICS OF THE TOOL AND THE COMPANY THAT PROVIDES IT:
1. COVERAGE. DEPENDING ON THE BRAND, WHETHER IT’S AN OEM OR AFTERMARKET TOOL, AND
THE VARIOUS MODELS, EACH SCAN TOOL IS GOING TO BE ABLE TO PROVIDE DIFFERENT
INFORMATION TO A REPAIRER. THEY WILL HAVE DIFFERENT ACCESS TO MANUFACTURER CODES,
AND THEY WILL BE ABLE TO ACCESS DIFFERENT LEVELS OF THE VEHICLE’S SYSTEMS. AS BERMAN
POINTS OUT, YOUR TOOL NEEDS TO COVER ALL ASPECTS OF EVERY ONE OF YOUR TOP-10
VEHICLES.
2. TRAINING/EASE OF USE. BERMAN SAYS THERE CAN BE A DRASTICALLY DIFFERENT LEARNING
CURVE BETWEEN BRANDS AND MODELS OF SCAN TOOLS. IN HIS SHOP, HE HAS TWO DIFFERENT
AFTERMARKET SCAN TOOLS—ONE FROM SNAP-ON AND ANOTHER FROM OTC—AND EACH, HE
SAYS, ARE RELATIVELY SIMPLE TO USE, AND BOTH COMPANIES PROVIDE AMPLE TRAINING.
3. TECHNICAL SUPPORT. THERE ARE STILL GOING TO BE TIMES WHEN A TECHNICIAN IS UNABLE
TO PULL A CODE, OR A CODE MAY NOT MAKE SENSE TO THE ISSUES THE VEHICLE HAS. BERMAN
SAYS THIS IS WHY HAVING STRONG TECHNICAL SUPPORT FROM THE COMPANY THAT PROVIDES
THE TOOL CAN HELP YOU UNDERSTAND WHETHER THERE IS AN ISSUE WITH THE TOOL ITSELF OR
SIMPLY USER ERROR.
4. UPGRADES AND UPDATES. THE MAKEUP OF VEHICLES CHANGES RAPIDLY, AND BERMAN SAYS
TO MAKE SURE YOU HAVE A TOOL THAT KEEPS UP WITH THE LATEST NEEDS OF REPAIRERS—
EITHER THROUGH SUBSCRIPTION UPDATES OR UPGRADES TO THE TOOL ITSELF. SOME
COMPANIES PROVIDE TRADE-IN OFFERS FOR UPGRADES, HE SAYS.
5. COST. THIS IS OBVIOUSLY AN IMPORTANT ASPECT, BUT BOTH KEITH AND BERMAN SAY TO KEEP
IT LAST ON THIS LIST. COST IS ONLY RELATIVE TO THE EFFECT THE TOOL WILL HAVE ON YOUR
BUSINESS, WHICH CAN EASILY BE MEASURED IN THE NEXT STEP.
STEP 3: ANALYZE THE RETURN ON INVESTMENT (ROI).
KEITH SAYS THAT, DESPITE WHAT SOME PEOPLE ASSUME ABOUT ROI, IT CAN ACTUALLY BE
PROPERLY CALCULATED BEFORE A PURCHASE IS EVER MADE. HERE ARE HIS THREE SIMPLE
STEPS TO DOING THAT:
1. STUDY THE PROBLEM. IN THE CASE OF A SCAN TOOL PURCHASE, KEITH SAYS TO LOOK AT HOW
THE CURRENT PROCESS PLAYS OUT IN YOUR SHOP WITHOUT THE NEW TOOL. LOOK FOR THE
INEFFICIENCIES: ARE YOUR TECHS FORCED TO SHARE OR SEARCH FOR THE CURRENT TOOLS?
DO THEY HAVE TO OUTSOURCE THE WORK BECAUSE YOU DON’T HAVE ONE AT ALL? WHAT’S THE
LOSS IN PRODUCTIVITY, CYCLE TIME, SALES, REVENUE AND PROFIT? ADD IT UP, KEITH SAYS, AND
SEE HOW MUCH YOUR SHOP IS LOSING IN BOTH EFFICIENCY OR DOLLARS. PUT A NUMBER TO IT.
2. UNDERSTAND HOW THE NEW TOOL MAKES A DIFFERENCE. BECAUSE YOU HAVE AN IDEA OF
THE TOOLS YOU’D LIKE TO PURCHASE FROM STEP 2, YOU CAN ANALYZE HOW THE NEW TOOL
WILL AFFECT THOSE EFFICIENCY AND REVENUE NUMBERS. HOW MUCH TIME DOES IT SHAVE OFF
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IN PRODUCTION? HOW MUCH MONEY DOES IT ADD TO YOUR SHOP’S SALES? AGAIN, PUT A
NUMBER TO IT.
3. COMPARE SAVINGS TO COST. KEITH SAYS THE FINAL STEP IS TO SIMPLY COMPARE THE
POTENTIAL MONEY SAVED AND THE IMPROVED EFFICIENCY CREATED TO THE TOTAL COST OF
THE TOOL INCLUDING SUBSCRIPTIONS. THAT’S YOUR ESTIMATED ROI, AND IT SHOULD GIVE YOU A
GOOD SENSE OF HOW LONG IT WILL TAKE TO ACHIEVE THAT BREAK-EVEN POINT. NOTE THAT THIS
CALCULATION IS TO HELP YOU BEST DETERMINE THE QUALITY OF YOUR PURCHASE; EVERYDAY
BUSINESS SITUATIONS CAN CAUSE CHANGES DOWN THE ROAD.
STEP 4: IMPLEMENT THE TOOL
WORKING THROUGH THE FIRST THREE STEPS SHOULD PROVIDE YOU WITH A TOOL OR LIST OF
TOOLS THAT WILL IMPROVE YOUR BUSINESS’S EFFICIENCY AND SALES—AT LEAST, IN THEORY.
THE KEY TO MAKING THAT PURCHASE, OR PURCHASES, TRULY HAVE VALUE IN YOUR SHOP
COMES FROM PROPER IMPLEMENTATION, KEITH SAYS.
BERMAN SAYS TO CREATE A STANDARD OPERATING PROCEDURE IN YOUR SHOP THAT OUTLINES
WHEN THE TOOL SHOULD BE USED AND WHO IS ASSIGNED TO PERFORM THE SCAN.
IN BERMAN’S SHOP, HE HAS TWO OF HIS TECHNICIANS FROM THE MECHANICAL SEGMENT
PERFORM THE SCANS BOTH DURING THE BLUEPRINTING PROCESS AND AFTER THE REPAIR IS
COMPLETED.
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ProScan Help : Diagnostic Trouble Code Breakdown
DTCs are composed of five characters; one letter followed by 4 digits.
Example DTCs:
 P0134
 P1155
 B0042
 C1132
 U3201
Digit 1 = System Identifier
Digit 1 System
P Powertrain
B Body
C Chassis
U Undefined
Digit 2 = Type of Code Definition
Generic:
Same definition for all manufacturers.
Manufacturer-Specific:
Definition varies among manufacturers.
Digit 2 Type of Code Definition
0 Generic
1 Manufacturer-Specific
2 P2xxx = Generic
B2xxx = Manufacturer-Specific
C2xxx = Manufacturer-Specific
U2xxx = Manufacturer-Specific
3 P30xx – P33xx = Manufacturer-Specific
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P34xx – P39xx = Generic
B3xxx = Generic
C3xxx = Generic
U3xxx = Generic
Digit 3 = Sub-System
Digit 3 Sub-System
1 Fuel & Air Metering
2 Fuel & Air Metering
(Injector Circuit Malfunction Only)
3 Ignition System or Misfire
4 Auxiliary Emission Control System
5 Vehicle Speed Control & Idle Control System
6 Computer Output Circuits
7-8 Transmission
Digits 4 & 5
The fourth and fifth digits of the DTC identify the specific problem.
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ProScan Help : Oxygen Sensor and Catalyst Configuration Example
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de 2ProScan Help : Oxygen Sensor and Catalyst Configurations
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OBDII: Past, Present and Future Pg 1 of 5 http://www.autotap.com
OBDII: PAST, PRESENT & FUTURE
All 1996 and newer model year passenger cars and light trucks are OBDII-equipped, but the first applications
were actually introduced back in ‘94 on a limited number of vehicle models.
What makes OBDII different from all the self-diagnostic systems that proceeded it is that OBDII is strictly
emissions oriented. In other words, it will illuminate the Malfunction Indicator Lamp (MIL) anytime a vehicle’s
emissions exceed 1.5 times the federal test procedure (FTP) standards for that model year of vehicle. That
includes anytime random misfires cause an overall rise in HC emissions, anytime the operating efficiency of the
catalytic converter drops below a certain threshold, anytime the system detects air leakage in the sealed fuel
system, anytime a fault in the EGR system causes NOX emissions to go up, or anytime a key sensor or other
emission control device fails. In other words, the MIL light may come on even though the vehicle seems to be
running normally and there are no real driveability problems.
The main purpose of the MIL lamp on an OBDII-equipped vehicle, therefore, is to alert you when your vehicle is
polluting so you’ll get their emission problems fixed. But as we all know, its easy to ignore warning lamps— until
steam is belching from under the hood or the engine is making horrible noises. That’s why regulators want to
incorporate OBDII into existing and enhanced vehicle emissions inspection programs. If the MIL lamp is found to
be on when a vehicle is tested, it doesn’t pass even if its tailpipe emissions are within acceptable limits.
WHY OBDII?
The problem with most vehicle inspection programs is that they were developed back in the 1980s to identify
"gross polluters." The tests were designed primarily to measure idle emissions on carbureted engines (which are
dirtiest at idle), and to check for only two pollutants: unburned hydrocarbons (HC) and carbon monoxide (CO).
The pass/fail cut points that were established for the various model years were also made rather lenient to
minimize the number of failures. Consequently, a lot of late model vehicles that shouldn’t be passing an
emissions test are getting through anyway.
Efforts to upgrade vehicle inspection programs to the new I/M 240 standards have stalled because of a lack of
public and political support. The I/M 240 program would have required "loaded-mode" emissions testing on a
dyno while the vehicle was driven at various speeds following a carefully prescribed driving trace. While this was
going on, the tailpipe gases would be analyzed to check not only for total emissions. The total emissions for the
entire 240-second driving cycle would then be averaged for a composite emission score that determines
whether or not the vehicle passed the test. Also included would be an evaporative purge flow test to measure
the flow rate of the canister purge valve, and an engine off pressure test of the evaporative emission control
system to check the fuel tank, lines and cap for leaks.
The I/M 240 program was to have been required in most areas of the country that don’t meet national ambient
air quality (NAAQ) standards. But after the program faltered in Maine, most states balked and only Colorado
went ahead with the program. The cost and complexity of the I/M 240 program combined with less than
enthusiastic public acceptance doomed it from the start. So it’s now up to the individual states to come up with
alternative plans for improving their air quality. An important element in many of those plans is OBDII.
A SHORT HISTORY WITH FAR REACHING IMPLICATIONS
The origins of OBDII actually date back to 1982 in California, when the California Air Resources Board (ARB)
began developing regulations that would require all vehicles sold in that state starting in 1988 to have an
onboard diagnostic system to detect emission failures. The original onboard diagnostic system (which has since
become known as OBDI) was relatively simple and only monitored the oxygen sensor, EGR system, fuel
delivery system and engine control module.
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OBDI was a step in the right direction, but lacked any requirement for standardization between different makes
and models of vehicles. You still had to have different adapters to work on different vehicles, and some systems
could only be accessed with costly "dealer" scan tools. So when ARB set about to develop standards for the
current OBDII system, standardization was a priority: a standardized 16-pin data link connector (DLC) with
specific pins assigned specific functions, standardized electronic protocols, standardized diagnostic trouble
codes (DTCs), and standardized terminology.
Another limitation of OBDI was that it couldn’t detect certain kinds of problems such as a dead catalytic
converter or one that had been removed. Nor could it detect ignition misfires or evaporative emission problems.
Furthermore, OBDI systems would only illuminate the MIL light after a failure had occurred. It had no way of
monitoring progressive deterioration of emissions-related components. So it became apparent that a more
sophisticated system would be required. The California Air Resources Board eventually developed standards for
the next generation OBD system, which were proposed in 1989 and became known as OBDII. The new
standards required a phase-in starting in 1994. The auto makers were given until the 1996 model year to
complete the phase-in for their California vehicles.
Similar standards were incorporated into the federal Clean Air Act in 1990 which also required all 49-state
vehicles to be OBDII equipped by 1996 -- with one loophole. The OBDII systems would not have to be fully
compliant until 1999. So some 1996 OBDII systems may lack one of the features normally required to meet the
OBDII specs, such as the evaporative emissions purge test.
EARLY OBDII APPLICATIONS
1994 vehicles equipped with the early OBD II systems include Buick Regal 3800 V6, Corvette, Lexus ES3000,
Toyota Camry (1MZ-FE 3.0L V6) and T100 pickup (3RZ-FE 2.7L four), Ford Thunderbird & Cougar 4.6L V8, and
Mustang 3.8L V6.1995 vehicles with OBDII include Chevy/GMC S, T-Series pickups, Blazer and Jimmy 4.3L V6,
Ford Contour & Mercury Mystique 2.0L four & 2.6L V6, Chrysler Neon, Cirrus and Dodge Stratus, Eagle Talon
2.0L DOHC (nonturbo), and Nissan Maxima and 240 SX.
Not all of these early applications are fully OBDII compliant, but do include the major diagnostic features of the
current system.
OBDII HARDWARE UPGRADES
Don’t think for a moment that OBDII is just a fancier version of self-diagnostic software. It’s that and much, much
more.OBDII-equipped vehicles typically have:
• Twice the number of oxygen sensors as non-OBDII vehicles(most of which are heated O2 sensors). The
additional O2 sensors are located downstream of the catalytic converter.
• More powerful powertrain control modules, with either16-bit (Chrysler) or 32-bit (Ford & GM) processors
to handle up to 15,000 new calibration constants that were added by OBDII.
• Electronically Erasable Programmable Read Only Memory(EEPROM) chips that allows the PCM to be
reprogrammed with revised or updated software changes using a terminal link or external computer.
• A modified evaporative emission control systems with a diagnostic switch for purge testing, or an
enhanced EVAP system with a vent solenoid, fuel tank pressure sensor and diagnostic test fitting,
• More EGR systems with a linear EGR valve that is electronically operated and has a pintle position
sensor.
• Sequential fuel injection rather than multiport or throttle body injection. Both a MAP sensor and MAF
sensor for monitoring engine load and airflow.
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TOOLING UP FOR OBDII
To work on your OBDII-equipped vehicle, you’ll need an OBDII scan tool such as AutoTap for PC or Palm PDA.
THAT PESKY MIL LAMP
Most technicians are pretty familiar with the operation of the "Check Engine" or "Malfunction Indicator Lamp"
(MIL) on late model vehicles. But on OBDII-equipped vehicles, it may seem like the MIL lamp has a mind of its
own.
On ‘96 General Motors J-, N- and H-body cars, several rental fleets have encountered problems with the MIL
lamp coming on because motorists and fleet personnel haven’t been using the correct refueling procedure when
filling the fuel tank with gas. On these cars, the OBDII system applies vacuum to the evaporative emissions
control system to check for air leakage. If the gas cap isn’t tight or the tank is filled while the key is on or the
engine is idling, it can trigger a false P0440 code causing the MIL light to come on. GM has not issued a
technical service bulletin on the problem, but is advising its dealers and fleet customers to reflash the EEPROM
with revised OBDII programming that waits to check the evaporative emissions system until the vehicle is in
motion.
Bad gas has also been causing some false MIL lights. When the vehicle is diagnosed, the technician finds a
P0300 random misfire code which would normally be set by a lean misfire condition due to a vacuum leak, low
fuel pressure, dirty injectors, etc., or an ignition problem such as fouled plugs, bad plug wires, weak coil, etc.
The OBDII self-diagnostics tracks misfires by individual cylinder, and considers up to a 2% misfire rate as
normal. But water in the gas or variations in the additive package in reformulated gasoline in some areas of the
country can increase the misfire rate to the point where it triggers a code.
To minimize the occurrence of false MIL lamps, the OBDII system is programmed so that the MIL lamp only
comes on if a certain kind of fault has been detected twice under the same driving conditions. With other faults
(those that typically cause an immediate and significant jump in emissions), the MIL light comes on after only a
single occurrence. So to correctly diagnose a problem, it’s important to know what type of code you’re dealing
with.
Type A diagnostic trouble codes are the most serious and will trigger the MIL lamp with only one occurrence.
When a Type A code is set, the OBDII system also stores a history code, failure record and freeze frame data to
help you diagnose the problem.
Type B codes are less serious emission problems and must occur at least once on two consecutive trips before
the MIL lamp will come on. If a fault occurs on one trip but doesn’t happen again on the next trip, the code won’t
"mature" and the light will remain off. When the conditions are met to turn on the MIL lamp, a history code,
failure record and freeze frame data are stored the same as with Type A codes.
A drive cycle or trip, by the way, is not just an ignition cycle, but a warm-up cycle. It is defined as starting the
engine and driving the vehicle long enough to raise the coolant temperature at least 40 degrees F (if the startup
temperature is less than 160 degrees F).
Once a Type A or B code has been set, the MIL will come on and remain on until the component that failed
passes a self-test on three consecutive trips. And if the fault involved something like a P0300 random misfire or
a fuel balance problem, the light won’t go out until the system passes a self-test under similar operating
conditions (within 375 rpm and 10% of load) that originally caused it to fail. That’s why the MIL lamp won’t go out
until the emissions problem has been repaired. Clearing the codes with your AutoTap scan tool or disconnecting
the powertrain control module’s power supply won’t prevent the lamp from coming back on if the problem hasn’t
been fixed. It may take one or more driving cycles to reset the code, but sooner or later the MIL lamp will go
back on if the problem is still there.
Likewise, the MIL won’t necessarily go on if you intentionally disconnect a sensor. It depends on the priority
ranking of the sensor (how it affects emissions), and how many driving cycles it takes for the OBDII diagnostics
to pick up the fault and set a code.
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As for Type C and D codes, these are non-emissions related. Type C codes can cause the MIL lamp to come on
(or illuminate another warning lamp), but Type D codes do not cause the MIL lamp to come on.
RUNNING AN OBDII DRIVE CYCLE
Suppose you’ve "fixed" an emissions problem on your OBDII-equipped vehicle. How can you check your work?
By performing what’s called an "OBDII drive cycle." The purpose of the OBDII drive cycle is to run all of the
onboard diagnostics. The drive cycle shold be performed after you’ve erased any trouble codes from the PCM’s
memory, or after the battery has been disconnected. Running through the drive cycle sets all the system status
"flags" so that subsequent faults can be detected.
The OBDII drive cycle begins with a cold start (coolant temperature below 122 degrees F and the coolant and
air temperature sensors within 11 degrees of one another).
NOTE: The ignition key must not be on prior to the cold start otherwise the heated oxygen sensor diagnostic
may not run.
1. As soon as the engine starts, idle the engine in drive for two and a half minutes with the A/C and rear
defrost on. OBDII checks oxygen sensor heater circuits, air pump and EVAP purge.
2. Turn the A/C and rear defrost off, and accelerate to 55 mph at half throttle. OBDII checks for ignition
misfire, fuel trim and canister purge.
3. Hold at a steady state speed of 55 mph for three minutes. OBDII monitors EGR, air pump, O2 sensors
and canister purge.
4. Decelerate (coast down) to 20 mph without braking or depressing the clutch. OBDII checks EGR and
purge functions.
5. Accelerate back to 55 to 60 mph at ¾ throttle. OBDII checks misfire, fuel trim and purge again.
6. Hold at a steady speed of 55 to 60 mph for five minutes. OBDII monitors catalytic converter efficiency,
misfire, EGR, fuel trim, oxygen sensors and purge functions.
7. Decelerate (coast down) to a stop without braking. OBDII makes a final check of EGR and canister
purge.
BEYOND OBDII
OBDII is a very sophisticated and capable system for detecting emissions problems. But when it comes to
getting motorists to fix emission problems, it’s no more effective than OBDI. Unless there’s some means of
enforcement, such as checking the MIL light during a mandatory inspection, OBDII is just another idiot light.
Currently under consideration are plans for OBDIII, which would take OBDII a step further by adding telemetry.
Using miniature radio transponder technology similar to that which is already being used for automatic electronic
toll collection systems, an OBDIII-equipped vehicle would be able to report emissions problems directly to a
regulatory agency. The transponder would communicate the vehicle VIN number and any diagnostic codes that
were present. The system could be set up to automatically report an emissions problem via a cellular or satellite
link the instant the MIL light comes on, or to answer a query from a cellular, satellite or roadside signal as to its
current emissions performance status.
What makes this approach so attractive to regulators is its effectiveness and cost savings. Under the current
system, the entire vehicle fleet in an area or state has to be inspected once every year or two to identify the 30%
or so vehicles that have emissions problems. With remote monitoring via the onboard telemetry on an OBDIII-
equipped vehicle, the need for periodic inspections could be eliminated because only those vehicles that
reported problems would have to be tested.
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On one hand, OBDIII with its telemetry reporting of emission problems would save consumers the
inconvenience and cost of having to subject their vehicle to an annual or biennial emissions test. As long as
their vehicle reported no emission problems, there’d be no need to test it. On the other hand, should an
emissions problem be detected, it would be much harder to avoid having it fixed—which is the goal of all clean
air programs anyway. By zeroing in on the vehicles that are actually causing the most pollution, significant gains
could be made in improving our nation’s air quality. But as it is now, polluters may escape detection and repair
for up to two years in areas that have biennial inspections. And in areas that have no inspection programs,
there’s no way to identify such vehicles. OBDIII would change all that.
The specter of having Big Brother in every engine compartment and driving a vehicle that rats on itself anytime it
pollutes is not one that would appeal to many motorists. So the merits of OBDIII would have to be sold to the
public based on its cost savings, convenience and ability to make a real difference in air quality. Even so, any
serious attempt to require OBDIII in the year 2000 or beyond will run afoul of Fourth Amendment issues over
rights of privacy and protection from government search and seizure. Does the government have the right to
snoop under your hood anytime it chooses to do so, or to monitor the whereabouts of your vehicle? These
issues will have to be debated and resolved before OBDIII stands a chance of being accepted. Given the
current political climate, such drastic changes seem unlikely.
Another change that might come with OBDIII would be even closer scrutiny of vehicle emissions. The misfire
detection algorithms currently required by OBDII only watch for misfires during driving conditions that occur
during the federal driving cycle, which covers idle to 55 mph and moderate acceleration. It does not monitor
misfires during wide open throttle acceleration. Full range misfire detection will be required for 1997 models.
OBDIII could go even further by requiring "fly-by-wire" throttle controls to reduce the possibility of misfires on the
coming generation of low emission and ultra low emission vehicles.So until OBDIII winds its way through the
regulatory process, all we have to worry about is diagnosing and repairing OBDII-equipped vehicles and all the
non-OBD vehicles that came before them.
AutoTap – OBDII Automotive Diagnostic Tool
http://www.autotap.com
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CHOOSING THE RIGHT SCAN TOOL FOR YOUR SHOP
HOW CHOOSING THE RIGHT DIAGNOSTIC SCAN TOOL CAN INCREASE YOUR SHOP’S PROFITABILITY
BRYCE EVANS
FIND THE RIGHT FIX EVERY SHOP HAS DIFFERENT USES FOR DIAGNOSTIC EQUIPMENT, MAKING
IT CRITICAL TO EVALUATE YOUR SPECIFIC NEEDS BEFORE MAKING A PURCHASE. THINKSTOCK
THE TASK, LOOKING BACK ON IT NOW, WAS PRETTY MUCH INSURMOUNTABLE—IMPOSSIBLE,
EVEN.
AS THE FORMER CO-CHAIR OF THE TOOL AND EQUIPMENT COMMITTEE FOR THE NATIONAL
AUTOMOTIVE SERVICE TASK FORCE (NASTF), DONNY SEYFER HEARD THE QUESTION ALL THE
TIME, FROM HIS FELLOW SHOP OWNERS, FROM REPAIR TECHNICIANS, EVERYONE: HOW DO YOU
PICK THE RIGHT SCAN TOOL?
SEEMED LIKE A SIMPLE QUESTION, HE THOUGHT, SIMPLE ENOUGH THAT NASTF SHOULD BE ABLE
TO PROVIDE A RESOUNDING, CLARIFYING ANSWER TO THE INDUSTRY.
SO, SEYFER’S TASK BECAME JUST THAT: CREATE A MATRIX THAT WOULD ALLOW SHOPS TO PICK
THE CORRECT SCAN TOOL BASED ON THEIR RESPECTIVE WORK-MIX NEEDS.
SEYFER FINISHED THE PROJECT IN 2012—OR, REALLY, HE SAYS, HE “ENDED” THE PROJECT.
“WE WERE AWARE OF IT GOING IN, BUT THE PROBLEM WAS THAT IT WAS ESSENTIALLY
IMPOSSIBLE TO EVER BE DONE WITH IT,” HE SAYS. “THERE ARE HUNDREDS OF TOOLS OUT THERE,
AND THEY’RE CHANGING ALL THE TIME WITH NEW UPDATES AND SOFTWARE. IT’S SOMETHING
THAT COULD NEVER BE FINISHED.”
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THE SCAN
TOOL MATRIX
THE MATRIX THAT SEYFER HELPED CREATE WITH NASTF, OFFICIALLY CALLED THE “VEHICLE
MANUFACTURER SERVICE INFORMATION MATRIX,” HELPS TO PROVIDE DETAILS ABOUT OEM
SERVICE INFORMATION, TOOLS AND TRAINING MATERIALS. IT CAN BE FOUND ON THE NASTF
WEBSITE.
STILL, SEYFER, OWNER OF SEYFER AUTOMOTIVE INC. IN WHEAT RIDGE, COLO., SAYS THAT IT’S
NECESSARY FOR EVERY SHOP TO GO THROUGH THEIR OWN SIMILAR PROCESS OF FINDING THE
CORRECT DIAGNOSTIC EQUIPMENT TO EFFECTIVELY REPAIR TODAY’S VEHICLES.
“HAVING [THE CORRECT DIAGNOSTIC SCAN TOOL] IS THE BIGGEST THING IN INCREASING
EFFICIENCY AND COMPETENCY—WHEN YOU HAVE THE RIGHT ONE,” HE SAYS. “AND, NOT HAVING
THE CORRECT ONE IS GOING TO BE YOUR BIGGEST HINDRANCE.
“VEHICLES TODAY HAVE SO MANY DIAGNOSTIC AND REFLASHING NEEDS, AND YOU’RE ONLY
GOING TO SEE MORE AND MORE.”
RESEARCHING AND PURCHASING SCAN TOOLS CAN FEEL LIKE A DAUNTING TASK, BUT, AS SEYFER
AND CARQUEST’S GEORGE LESNIAK HELP POINT OUT, THERE ARE SIMPLE STEPS EVERY SHOP
CAN GO THROUGH TO ENSURE IT EQUIPS ITS TECHNICIANS WITH THE RIGHT DIAGNOSTIC
EQUIPMENT.
TEACH A TECH TO FISH: THE CHALLENGES
LESNIAK IS THE CURRICULUM DEVELOPMENT MANAGER FOR THE CARQUEST TECHNICAL
INSTITUTE. HE’S BEEN TEACHING AND WRITING COURSES FOR TECHNICIAN TRAINING FOR 14
YEARS, AND HE HAS PERSONALLY RUN THOROUGH TEST TRIALS ON THE PRODUCTS OF A
NUMBER OF AFTERMARKET AND OEM SCAN TOOL PROVIDERS.
HE KNOWS DIAGNOSTICS, AND HE SAYS THAT BEFORE ANY SHOP OWNER SEES A SCAN TOOL AS
A “SILVER BULLET” OR A “QUICK FIX” TO THEIR DIAGNOSTIC DILEMMAS, THEY NEED TO ASK
THEMSELVES ONE QUESTION: HOW MUCH TIME AM I WILLING TO INVEST IN LEARNING THE
ADVANCED FUNCTIONS OF THE SCAN TOOL I PURCHASE?
“TECHNICIANS WANT TO KNOW WHAT’S WRONG WITH THE VEHICLE THEY ARE TROUBLESHOOTING
TODAY,” HE SAYS. “THIS IS WHY SCAN TOOLS WITH BUILT-IN DIAGNOSTIC TIPS AND TRICKS ARE SO
POPULAR. I BELIEVE THIS IS A FUNDAMENTALLY WRONG APPROACH. REMEMBER THE OLD ADAGE,
‘IF YOU GIVE A MAN A FISH … .’ WELL, THE SAME HOLDS TRUE FOR TROUBLESHOOTING. IF YOU
GIVE THE TECHNICIAN AN ANSWER, HE MAY FIX A CAR BUT IF YOU TEACH A TECHNICIAN HOW THE
VEHICLE WORKS, HOW HIS DIAGNOSTIC EQUIPMENT WORKS AND HOW TO THINK FOR HIS OR
HERSELF, THEY CAN FIX NEARLY ANYTHING.”
BOTTOM LINE: A SCAN TOOL IS NOT A CRUTCH, LESNIAK SAYS, EVEN THOUGH MANY TECHNICIANS
AND SHOPS LIKE TO USE IT AS ONE.
AND THAT’S JUST ONE OF THE MANY CHALLENGES THAT THESE TOOLS PRESENT. HERE ARE
FOUR OTHERS SEYFER AND LESNIAK SAY TO KEEP IN MIND:
1. NO STANDARDIZATION. DESPITE THE PENDING CHANGES WITH RIGHT TO REPAIR LEGISLATION,
THERE IS NO UNIVERSAL, STANDARDIZED APPROACH TO DIAGNOSTICS RIGHT NOW, , SEYFER
SAYS. AND BECAUSE OF THAT, THE MAJORITY OF SCAN TOOLS OPERATE AND ROUTE THROUGH
THE VEHICLE’S COMPUTER SYSTEM DIFFERENTLY. THAT’S WHY CERTAIN SCAN TOOLS WORK—OR
EVEN PARTIALLY WORK—ON CERTAIN VEHICLES AND NOT ON OTHERS. IT’S ANOTHER REASON
TECHS NEED TO UNDERSTAND THE TOOL AND THE VEHICLE SYSTEM, LESNIAK SAYS.
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2. REVERSE ENGINEERING. BECAUSE AFTERMARKET TOOL MAKERS ARE NOT GIVEN COMPLETE
VEHICLE INFORMATION, THEIR TOOLS MUST BE REVERSE ENGINEERED TO BE ABLE TO WORK,
AND THAT OFTEN CAN LEAD TO MISSED CAPABILITIES.
3. NOTHING IS UNIVERSAL—EVEN IF IT CLAIMS TO BE. ONE OF THE MOST DIFFICULT THINGS FOR
SHOPS IS TO WEIGH A TOOL’S CLAIMED ABILITY AGAINST ITS ACTUAL CAPABILITIES, SEYFER
SAYS. SIMPLY PUT: THERE IS NO ONE TOOL THAT CAN DO EVERYTHING FOR EVERY VEHICLE, OR
EVEN COME CLOSE. AND THAT BRINGS US TO ...
4. INFORMATION GAPS. WHETHER IT’S BECAUSE OF REVERSE ENGINEERING OR EVEN SIMPLY
NOT BEING THE LATEST VERSION OF A TOOL, THE EQUIPMENT WILL HAVE INFORMATION GAPS.
THE PROBLEM IS, LESNIAK SAYS, A SCAN TOOL ONLY SHOWS YOU WHAT IT CAN DO, NOT WHAT IT
CAN’T—YET ANOTHER REASON TO UNDERSTAND THE VEHICLES YOU WORK ON, HE SAYS.
HUNTING FOR ANSWERS: CHOOSING YOUR TOOL
EVERY SHOP WILL HAVE DIFFERENT NEEDS AND USES FOR A SCAN TOOL, SEYFER SAYS, SO IT’S
CRITICAL TO IDENTIFY YOUR FACILITY’S SPECIFIC NEEDS FROM THE EQUIPMENT. HE AND LESNIAK
OUTLINED SIX STEPS FOR DOING THAT.
STEP 1: LOOK AT WHAT YOU WORK ON. TAKE A LOOK AT YOUR WORK MIX, SEYFER SAYS. WHAT
VEHICLES DO YOU WORK ON THE MOST? WHAT MAKES, MODELS AND YEARS DO YOU SEE MOST
OFTEN? “THE MORE SPECIFIC AND ‘SPECIALIZED’ YOU CAN BE WITH WHAT YOU WORK ON, THE
BETTER OFF YOU’LL BE,” HE SAYS. PICK YOUR 10 MOST WORKED-ON VEHICLES, LESNIAK SAYS,
AND FIGURE OUT YOUR NEEDS FOR THOSE.
STEP 2: LOOK AT WHAT YOU DON’T WORK ON. OF COURSE, A SCAN TOOL SHOULD BE ABLE TO
HELP YOU BRING IN ADDITIONAL VEHICLES, JOBS, REVENUE AND, ULTIMATELY, PROFITABILITY,
LESNIAK SAYS. “PEOPLE ASK ME ALL THE TIME, ‘WHAT SCAN TOOL SHOULD I GET?’” HE SAYS. “AND
MY FIRST RESPONSE IS ALWAYS ASKING THEM, ‘WHAT DON’T YOU WORK ON?’ THEN I ASK, ‘WHY?’
USUALLY, THAT HELPS YOU IDENTIFY VEHICLES IN YOUR AREA YOU’RE MISSING OUT ON. FOR AN
EXAMPLE, SEYFER AND HIS SHOP RECENTLY INVESTED IN EQUIPMENT TO PROPERLY DIAGNOSE
JAGUARS, AS HE SAW MANY IN HIS AREA AND VERY FEW SHOPS THAT WERE TAKING ADVANTAGE
OF IT.
STEP 3: RESEARCH THE TOOLS. HERE’S WHERE SHOPS OFTEN GET DISCOURAGED, LESNIAK
SAYS, BUT IF YOU HAVE THE PROPER APPROACH AND THE CORRECT VISION FOR YOUR SHOP’S
WORK MIX (STEPS 1 AND 2), THEN YOU’VE ALREADY NARROWED IT DOWN QUITE A BIT. THERE ARE
SIX THINGS TO CONSIDER:
COVERAGE. WHAT DATA DOES THE TOOL COME WITH? WHAT SUBSCRIPTIONS? WHAT VEHICLES
DO THOSE COVER? WHAT MAKES AND MODEL YEARS? SEYFER SAYS THAT, BECAUSE OF
CHANGES IN VEHICLE DESIGN AND CAPABILITIES, NOT EVEN OEM TOOLS COVER ALL OF THEIR
OWN VEHICLES. AND SOME ARE ABLE TO ACCESS MULTIPLE MANUFACTURERS. YOU NEED TO
FULLY UNDERSTAND WHAT EACH TOOL IS CAPABLE OF READING.
TRAINING/EASE OF USE. MOST AFTERMARKET TOOLS ARE EASY TO “PICK UP AND GO WITH,”
LESNIAK SAYS. OEM TOOLS OFTEN COME WITH A STEEPER LEARNING CURVE FOR FIRST-TIME
USERS. TRY TO GET A FEEL FOR THE TIME AND EFFORT IT WILL TAKE FOR YOUR STAFF TO
MASTER THE EQUIPMENT, AND WHAT TRAINING THE MANUFACTURER OR PROVIDER OFFERS.
COMPATIBILITY. SOME TOOLS CAN BE USED THROUGH A WINDOWS-BASED PC OR LAPTOP, AND
SEYFER SAYS THAT OFTEN MEANS ONE SINGLE TOOL CAN WORK WITH A NUMBER OF DIFFERENT
VERSIONS OF MANUFACTURER SOFTWARE TO PROVIDE A WIDE RANGE OF COVERAGE.
Page 40

TECHNICAL SUPPORT. SOME TOOL MAKERS AND VEHICLE MANUFACTURERS PROVIDE HOTLINES
OF SORTS TO CALL FOR ADDITIONAL INFORMATION OR FOR DIFFICULT DIAGNOSES. UNDERSTAND
WHAT EACH TOOL HAS TO OFFER.
UPGRADES/UPDATES. AS PER SEYFER’S DILEMMA WITH HIS NASTF MATRIX, TOOLS ARE
CONSTANTLY BEING UPGRADED AND UPDATED. HE SAYS TO RESEARCH THE COMPANIES YOU’RE
CONSIDERING AND SEE WHAT THEY OFFER IN TERMS OF UPGRADES—NOT JUST FOR THE
PURPOSE OF THE EQUIPMENT BUT ALSO TO SEE IF THEY CUT ANY DEALS ON UPDATING THE
TOOL.
COST. THERE’S GOING TO BE A LARGE DISCREPANCY IN PRICE BETWEEN TOOL MAKERS. THIS IS
WHY UNDERSTANDING YOUR WORK MIX IS IMPORTANT TO GRASP THE VALUE OF THE TOOL.
STEP 4: ANALYZE THE RETURN. THERE ARE A LOT OF WAYS TO TRY TO ANALYZE HOW VALUABLE
A SCAN TOOL IS IN A SHOP. SEYFER LIKES TO SORT OF LOW-BALL THE RETURN AND ONLY
COMPARE THE COST OF THE TOOL (INCLUDING SUBSCRIPTIONS AND UPGRADES) TO THE AMOUNT
OF MONEY HE MAKES ON DIAGNOSTIC CHARGES. OBVIOUSLY, HE SAYS, THAT DOESN’T TAKE INTO
ACCOUNT ANY IMPROVEMENTS IN EFFICIENCY, CAR COUNT, ETC. HE SAYS IT HELPS GIVE HIM AN
ABSOLUTE MINIMUM THAT CAN SERVE TO DIRECTLY PAY OFF THE TOOL.
STEP 5: DEMO THE TOOLS. LESNIAK SAYS TO BE WARY OF ANY COMPANY THAT ISN’T CONFIDENT
ENOUGH IN ITS PRODUCT TO LET YOU HAVE IT FOR A FULL, ON-YOUR-OWN TRIAL PERIOD.
“RECEIVING A DEMO FROM THEM IS NOT GOOD ENOUGH,” HE SAYS. “YOU NEED TO HAVE IT IN
YOUR TECHNICIAN’S HANDS AND LET THEM BE ABLE TO SEE ITS FULL CAPABILITIES ON YOUR
ACTUAL WORK MIX. TESTING THE TOOL ON YOUR OWN IS THE MOST IMPORTANT THING YOU CAN
DO TO MAKE THE CORRECT DECISION.”
STEP 6: IMPLEMENT THE TOOLS. ALTHOUGH THIS STEP MUST COME AFTER YOU SELECTED AND
PURCHASED A TOOL, IT WILL ALSO HELP TO CONFIRM YOUR DECISION. DON’T JUST SIMPLY BUY
DIAGNOSTIC EQUIPMENT AND HAND IT OFF TO THE TECHNICIAN. CREATE PROCESSES AND
SYSTEMS FOR YOUR SHOP TO USE IT CORRECTLY, SEYFER SAYS, AND MAKE SURE TO MARKET
YOUR CAPABILITIES.
KEEP IT SIMPLE
LESNIAK AND SEYFER BOTH FEEL THAT CHOOSING A SCAN TOOL FOR YOUR SHOP CAN BE A
DAUNTING TASK. THE IMPORTANT THING TO REMEMBER, SEYFER SAYS, IS THAT YOU NEED TO
FIND THE BEST FIT FOR YOUR BUSINESS—NOT JUST THE FLASHIEST, MOST EXPENSIVE
EQUIPMENT (OR THE MOST AFFORDABLE, FOR THAT MATTER).
GET AS MUCH INFORMATION AS YOU CAN, LESNIAK SAYS. TALK WITH OTHER SHOP OWNERS, TALK
WITH YOUR VENDORS, ASK ABOUT IT IN 20 GROUP MEETINGS, ASSOCIATION GATHERINGS, ON
MESSAGE BOARDS—ANYWHERE YOU CAN. THERE’S PLENTY OF INFORMATION ONLINE ABOUT
EACH TOOL AND IATN, THE EQUIPMENT AND TOOL INSTITUTE (ETI), NASTF AND OTHERS HAVE
DETAILED INFORMATION.
IN THE END, THOUGH, LESNIAK SAYS TO TRY TO MAKE THE PROCESS AS SIMPLE AS YOU CAN.
“THERE’S NO ONE ANSWER FOR ANY SHOP,” HE SAYS. “BUT, IF YOU DO YOUR RESEARCH AND
TEST THE [SCAN TOOLS] OUT BEFOREHAND, YOU CAN MAKE IT A WHOLE LOT EASIER ON
YOURSELF.”
Page 41

Magnaflow Exhaust Products
As promised from last month, more on OBD. Refer to our Website, Magnaflow.com for archived Bulletins.
(http://www.magnaflow.com/07techtips/techbulletins.asp)
Data Stream
Referred to as Current Data or Live Data, this information is available to the technician using a Scan Tool. The number of PIDS (Parameter Identification)
available at any given time will depend on a couple of different factors. The particular vehicle (Manufacturer) involved will have the greatest influence on the
amount of data available. Followed by the type of Scan Tool used and whether you are viewing the data on the Global OBD II side or Manufacture Specific, aka
Enhanced Mode. (Figure 1) Most Scan Tools will have options for viewing the data in different formats such as digital or graphing mode. Graphing can be
particularly useful when looking at Oxygen Sensor activity. (Figure 2) The data available will consist of inputs and outputs, calculated values and system status
information.
Viewing data and becoming proficient at recognizing problem areas is one of the skills we spoke of in last months Bulletin (TB-80016). Part of any training on a
particular tool is the repetitive process of using it over and over until you begin to recognize when certain data doesn’t look right. This process will then lead you
toward a problem area where further testing will reveal the fault. You can not recognize bad data until you have looked at enough good data. One item to be aware
of is the practice of substituting good data values for suspect ones. Due to something called Adaptive Strategy, when the PCM suspects that a particular input may
not be reporting accurately, it will substitute a known good value for that sensor and run the vehicle on learned values. This will only show up in Enhanced Mode
as Global OBD II will always display actual values. This should not deter you from viewing in Enhanced Mode. It has always been my practice to look at codes
and data in both modes.
FIGURE 1 FIGURE 2
Freeze Frame
Freeze frame is a “snap shot” of data taken when a code is set. This can be very valuable information as it allows the technician an opportunity to duplicate the
conditions under which the trouble code was recorded. The number of freeze frame events recorded and viewable by the technician will again depend on the
vehicle and scan tool being used. Early systems could only store one batch of information, if more than one code was recorded we would typically only be able to
view the Freeze Frame for the last code set. Changes in both OBD and Scan Tool technology have allowed us to have multiple sets of information available for
multiple codes set. One exception is that of Misfire. Misfire codes and subsequent data take precedent and will overwrite any previous freeze data stored. Be
aware that all freeze frame information is lost when codes are cleared.
On Board Diagnostics Part II
Bulletin TB-80017
December, 2009
Page 42

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