Halderman ch107 lecture
Upcoming SlideShare
Loading in...5
×
 

Halderman ch107 lecture

on

  • 1,378 views

 

Statistics

Views

Total Views
1,378
Views on SlideShare
1,376
Embed Views
2

Actions

Likes
0
Downloads
41
Comments
0

1 Embed 2

http://moodle.lattc.edu 2

Accessibility

Categories

Upload Details

Uploaded via as Microsoft PowerPoint

Usage Rights

© All Rights Reserved

Report content

Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
  • Full Name Full Name Comment goes here.
    Are you sure you want to
    Your message goes here
    Processing…
Post Comment
Edit your comment
  • Figure 107-1 On most vehicles equipped with ABS, the amber ABS and red BRAKE warning lamp should come on as a bulb check when the ignition is first switched on.
  • Figure 107-2 A thorough visual inspection should include carefully inspecting around the electrohydraulic unit for signs of obvious problems or the installation of aftermarket devices such as alarm systems.
  • Figure 107-3 General Motors diagnostic connector on a pre- 1996 vehicle. Flash codes are available by using a jumper wire to ground (terminal A) to terminal H.
  • Figure 107-4 Connecting a jumper wire from the diagnostic connector to ground. The exact location of this diagnostic connector varies with the exact vehicle model and year.
  • Figure 107-5 Chrysler diagnostic connector location varies with the model and year.
  • Figure 107-6 A scan tool is the recommended method to use to access General Motors Teves Mark IV systems.
  • Figure 107-7 The Delphi (Delco) VI attaches to the side of the master cylinder and connects hydraulically through transfer tube assemblies.
  • Figure 107-8 A breakout box is being used to diagnose an ABS problem. The controller (computer) is located in the trunk of this vehicle, and a digital multimeter is being used to measure resistance and voltage at various points in the system, following the service manual procedure.
  • Figure 107-9 Typical wheel speed sensor. When a tooth on the sensor ring is close to the sensor, the strength of the magnetic field is stronger because the metal of the tooth conducts magnetic lines of force better than air. When the tooth moves away, the magnetic field strength is reduced. It is this changing magnetic field strength that produces the changing voltage. Frequency of the signal is determined by the speed of the rotating sensor.
  • Figure 107-10 Measuring the resistance of a wheel speed sensor.
  • Figure 107-11 A scope can be used to check for proper operation of a wheel speed sensor.
  • Figure 107-12 A broken tooth on a wheel speed sensor tone ring shows on the scope trace as a missing wave.
  • Figure 107-13 Use a nonmagnetic brass or plastic feeler gauge to check wheel speed sensor gap. A steel gauge would be attracted by the magnet in the sensor and would produce a drag on the gauge as it is moved between the sensor and the tone ring. This drag could be interpreted as a correct clearance reading.
  • Figure 107-14 (a) Always use a nonferrous (brass or plastic) feeler (thickness) gauge when measuring the gap between the toothed ring and the wheel speed sensor.
  • Figure 107-14 (b) Sometimes a sensor is equipped with a paper spacer that is the exact thickness of the spacing required between the toothed ring and the sensor. If equipped, the sensor is simply installed with the paper touching the toothed wheel. A typical gap ranges from 0.020 to 0.050 in. (0.5 to 1.3 mm).
  • CHART 107–1
  • CHART 107–1 (continued)
  • CHART 107–1 (continued)

Halderman ch107 lecture Halderman ch107 lecture Presentation Transcript

  • ABS DIAGNOSIS AND REPAIR 107
  • Objectives
    • The student should be able to:
      • Prepare for Brakes (A5) ASE certification test content area “F” (Antilock Brake System Diagnosis and Repair).
      • Explain the purpose and function of the red brake warning lamp.
      • Describe normal ABS dash lamp operation.
      • Discuss visual inspection of the various types and brands of ABS.
  • Objectives
    • The student should be able to:
      • Explain how to retrieve trouble codes.
      • List the methods used to clear trouble codes.
      • Explain the various methods for bleeding ABS systems.
      • Discuss methods and tools needed to diagnose and service an ABS-equipped vehicle.
  • ABS DIAGNOSTIC PROCEDURE
  • ABS Diagnostic Procedure
    • To diagnose an ABS problem use the following steps:
      • STEP 1: Verify the customer concern.
      • STEP 2: Perform a visual inspection including leaks or faults in the following:
        • Master cylinder
        • Electrohydraulic control unit
  • ABS Diagnostic Procedure
    • To diagnose an ABS problem use the following steps:
      • STEP 2: Perform a visual inspection including leaks or faults in the following:
        • Flexible brake hoses
  • ABS Diagnostic Procedure
    • To diagnose an ABS problem use the following steps:
      • STEP 2: Perform a visual inspection including leaks or faults in the following:
        • Brake lines and fittings
  • ABS Diagnostic Procedure
    • To diagnose an ABS problem use the following steps:
      • STEP 2: Perform a visual inspection including leaks or faults in the following:
        • Calipers and/or wheel cylinders
  • ABS Diagnostic Procedure
    • To diagnose an ABS problem use the following steps:
      • STEP 3: Check for stored diagnostic trouble codes.
      • STEP 4: Complete the repair.
      • STEP 5: Verify the repair.
  • BRAKE WARNING LAMP OPERATION
  • Brake Warning Lamp Operation
    • When visually diagnosing an antilock braking system problem first check the status of the brake warning lamps
  • Brake Warning Lamp Operation
    • Red Brake Warning Lamp
      • A red brake warning lamp (RBWL) warns of a possible dangerous failure in the base brakes
  • Brake Warning Lamp Operation
    • Red Brake Warning Lamp
      • This lamp will also light if the parking brake is applied and may light due to an ABS failure
  • Brake Warning Lamp Operation
    • Amber ABS Warning Lamp
      • The amber ABS warning lamp usually comes on after an engine start during the initialization or start-up self-test sequence
      • The amount of time the lamp remains on after the ignition is turned on varies with design
  • Figure 107-1 On most vehicles equipped with ABS, the amber ABS and red BRAKE warning lamp should come on as a bulb check when the ignition is first switched on.
  • THOROUGH VISUAL INSPECTION
  • Thorough Visual Inspection
    • A thorough visual inspection should include the following items:
      • Brake fluid level: check condition and level
      • Brake fluid leaks: check for cracks or other damage in flexible lines damage and check for wetness at any fitting or steel brake line
  • Thorough Visual Inspection
    • A thorough visual inspection should include the following items:
      • Fuses and fusible links: check all ABS-related fuses
      • Wiring and connections: check all wiring, especially wheel speed sensor leads
  • Thorough Visual Inspection
    • A thorough visual inspection should include the following items:
      • Wheel speed sensors: check that the sensor ring teeth are not damaged and clean debris from the sensor if possible
  • Thorough Visual Inspection
    • NOTE: Most wheel speed sensors are magnetic and therefore can attract and hold metallic particles. Be sure to remove any metallic debris from around the magnetic wheel speed sensor.
  • Thorough Visual Inspection
    • A thorough visual inspection should include the following items:
      • Base brake components: check that all base brake components, including disc brake calipers, drum brake wheel cylinders, and related components are in good working condition
  • Thorough Visual Inspection
    • A thorough visual inspection should include the following items:
      • Parking brake: check that the brake is correctly adjusted and fully released
  • Thorough Visual Inspection
    • A thorough visual inspection should include the following items:
      • Wheel bearings: check that all wheel bearings are free of defects and adjusted properly
  • Thorough Visual Inspection
    • A thorough visual inspection should include the following items:
      • Wheels and tires: check for correct size, proper inflation, and legal tread depth
    ?
  • Figure 107-2 A thorough visual inspection should include carefully inspecting around the electrohydraulic unit for signs of obvious problems or the installation of aftermarket devices such as alarm systems.
  • TEST DRIVE AND VERIFY THE FAULT
  • Test Drive and Verify the Fault
    • Many ABS systems and diagnostic trouble codes (DTCs) will not set unless the vehicle is moving
    • Start the engine and observe the red and amber brake warning lamps
    • If the red brake warning lamp is on, the base brakes may not be functioning correctly
  • Test Drive and Verify the Fault
    • NOTE: Some ABS units, such as the Delphi VI, will cause the brake pedal to move up and down slightly during cycling of the valves during the self-test. Each system has unique features. The service technician will have to learn to avoid attempting to repair a problem that is not a fault of the system.
  • Test Drive and Verify the Fault
    • NOTE: Some systems are diagnosed by “antilock” and “brake” warning lamps, vehicle symptoms, and the use of a breakout box.
  • RETRIEVING DIAGNOSTIC TROUBLE CODES
  • Retrieving Diagnostic Trouble Codes
    • The exact procedure depends on the type of ABS and vehicle
    • Always consult factory service information for the vehicle being diagnosed
  • Retrieving Diagnostic Trouble Codes
    • Some systems can only display flash codes (flashing ABS or brake lamp in sequence)
    • Some systems can perform self-diagnosis and display all information on a scan tool
  • Retrieving Diagnostic Trouble Codes
    • NOTE: With some early antilock braking systems, the diagnostic trouble code is lost if the ignition is turned “off” before grounding the diagnostic connector.
  • KELSEY-HAYES ANTILOCK (NONINTEGRAL)
  • Kelsey-Hayes Antilock (Nonintegral)
    • The Kelsey-Hayes rear-wheel antilock uses two solenoids and valves to control the rear-wheel brakes
    • Kelsey-Hayes four-wheel antilock uses the computer to pulse the valves
    • This pumping is called pulse-width modulated (PWM) and the valve is called a PWM valve
  • Kelsey-Hayes Antilock (Nonintegral)
    • GM trucks’ (RWAL) DTCs are retrieved by flash codes or scan data through the use of a scan tool or connect H to A at the data link connector (DLC)
    • Ford RABS DTCs are retrieved by jumper lead flash codes only
    • Dodge light truck DTCs are retrieved by ground diagnostic connections
  • Kelsey-Hayes Antilock (Nonintegral)
    • NOTE: Be sure that the brake warning lamp is on before trying to retrieve DTCs. If the lamp is not on, a false code 9 could be set.
  • Kelsey-Hayes Antilock (Nonintegral)
    • NOTE: If the ignition is turned off, the failure code will be lost unless it is a hard code that will be present when the ignition is turned back on.
  • Kelsey-Hayes Antilock (Nonintegral)
    • NOTE: A scan tool may or may not be able to retrieve or display diagnostic trouble codes. Check with the technical literature for the specific vehicle being scanned.
  • Figure 107-3 General Motors diagnostic connector on a pre- 1996 vehicle. Flash codes are available by using a jumper wire to ground (terminal A) to terminal H.
  • Figure 107-4 Connecting a jumper wire from the diagnostic connector to ground. The exact location of this diagnostic connector varies with the exact vehicle model and year.
  • Figure 107-5 Chrysler diagnostic connector location varies with the model and year.
  • BOSCH 2 ABS (NONINTEGRAL)
  • Bosch 2 ABS (Nonintegral)
    • Retrieving Diagnostic Trouble Codes
      • On General Motors vehicles connect A to H at the data link connector (DLC)
      • For most systems, a scan tool should be used, if available
  • TEVES MARK IV
  • Teves Mark IV
    • The Teves Mark IV is a nonintegral (remote) ABS system
      • Retrieving diagnostic trouble codes
        • Only a bidirectional scan tool connected to the data link connector (DLC) can be used
  • Figure 107-6 A scan tool is the recommended method to use to access General Motors Teves Mark IV systems.
  • Teves Mark IV
    • The Teves Mark IV is a nonintegral (remote) ABS system
      • Clearing diagnostic trouble codes
        • On some vehicles, a scan tool is required
  • Teves Mark IV
    • The Teves Mark IV is a nonintegral (remote) ABS system
      • Clearing diagnostic trouble codes
        • Driving over 20 mph (32km/h) will clear codes on some vehicles
  • Teves Mark IV
    • The Teves Mark IV is a nonintegral (remote) ABS system
      • Clearing diagnostic trouble codes
        • Disconnecting the battery will clear the codes, but will cause loss of other "keep alive" functions
  • DELPHI (DELCO) ABS-VI (NONINTEGRAL)
  • Delphi (Delco) ABS-VI (Nonintegral)
    • The Delphi (Delco) ABS-VI is unique from all other ABS systems because it uses a motor-driven ball screws and pistons for brake pressure to reduce, hold, and apply
  • Delphi (Delco) ABS-VI (Nonintegral)
    • Retrieving Diagnostic Codes
      • This system has extensive self-diagnostic capability
      • A scan tool designed to work with the Delphi VI system is required to access this information
  • Figure 107-7 The Delphi (Delco) VI attaches to the side of the master cylinder and connects hydraulically through transfer tube assemblies.
  • WHEEL SPEED SENSOR DIAGNOSIS
  • Wheel Speed Sensor Diagnosis
    • Wheel speed sensor (WSS) circuits are often the cause of many ABS problems
    • These components may suffer from physical damage, buildup of metallic debris on the sensor tip, corrosion, poor electrical connections, and damaged wiring
  • Wheel Speed Sensor Diagnosis
    • Test a WSS by measuring its output voltage and circuit continuity
    • A breakout box (BOB) cable connects to the ABS harness near the ABS module
    • All WSS resistance checks, including the wiring to the sensors, can be measured at one location
  • Figure 107-8 A breakout box is being used to diagnose an ABS problem. The controller (computer) is located in the trunk of this vehicle, and a digital multimeter is being used to measure resistance and voltage at various points in the system, following the service manual procedure.
  • Figure 107-9 Typical wheel speed sensor. When a tooth on the sensor ring is close to the sensor, the strength of the magnetic field is stronger because the metal of the tooth conducts magnetic lines of force better than air. When the tooth moves away, the magnetic field strength is reduced. It is this changing magnetic field strength that produces the changing voltage. Frequency of the signal is determined by the speed of the rotating sensor.
  • Wheel Speed Sensor Diagnosis
    • Resistance Measurement
      • The resistors of most WSS range from 800 Ω to 1,400 Ω
      • A reading of about 1,000 ohms or 1 KΩ indicates proper sensor coil resistance
  • Figure 107-10 Measuring the resistance of a wheel speed sensor.
  • Wheel Speed Sensor Diagnosis
    • Checking For Short-To-Ground
      • Connect either lead of an ohmmeter to one of the WSS wires and the other to a good, clean chassis ground
  • Wheel Speed Sensor Diagnosis
    • Checking For Short-To-Ground
      • The resistance should be infinity (OL)
      • If resistance reading is low the sensor or sensor wiring must be replaced
  • Wheel Speed Sensor Diagnosis
    • AC Voltage Check
      • Connect a digital meter to the WSS terminals or input to the controller in the breakout box and set the meter to read AC volts
      • Rotate the wheel by hand at a rate of one revolution per second
  • Wheel Speed Sensor Diagnosis
    • AC Voltage Check
      • A good WSS should produce voltage of at least 0.1 volt (100 mV)
      • A sensor voltage of lower than 0.1 volt (100 mV) may be caused by three things:
        • Excessive clearance between the sensor and tone ring.
  • Wheel Speed Sensor Diagnosis
    • AC Voltage Check
      • A sensor voltage of lower than 0.1 volt (100 mV) may be caused by three things:
        • Buildup of debris on the end of the sensor.
  • Wheel Speed Sensor Diagnosis
    • AC Voltage Check
      • A sensor voltage of lower than 0.1 volt (100 mV) may be caused by three things:
        • Excessive resistance in the sensor or sensor wiring.
  • Wheel Speed Sensor Diagnosis
    • DC Bias Voltage
      • Some ABS systems apply a 2.5 volt DC voltage to the wheel speed sensors, called a bias voltage
  • Wheel Speed Sensor Diagnosis
    • DC Bias Voltage
      • Bias voltage is used by the ABS controller to detect fault in the sensor or sensor wiring such as an open circuit or a short to ground
  • Wheel Speed Sensor Diagnosis
    • Scope Testing
      • Attach the scope leads to the sensor terminals or to the input connector on the breakout box
      • Rotate the wheel by hand or by using engine power with all four wheels off the ground
  • Wheel Speed Sensor Diagnosis
    • Scope Testing
      • A good WSS should produce an alternating current (AC) sine wave signal that increases in frequency and amplitude with increasing wheel speed
      • Damaged or missing teeth on the tone ring will cause flat spots or gaps in the sine wave pattern
  • Wheel Speed Sensor Diagnosis
    • Scope Testing
      • A bent axle or hub will produce a wavelike pattern that fluctuates as the strength of the sensor signal changes with each revolution
  • Figure 107-11 A scope can be used to check for proper operation of a wheel speed sensor.
  • Figure 107-12 A broken tooth on a wheel speed sensor tone ring shows on the scope trace as a missing wave.
  • Wheel Speed Sensor Diagnosis
    • Scan Tool Testing
      • As an assistant drives the vehicle, connect the scan tool and monitor the speed of all of the sensors
  • Wheel Speed Sensor Diagnosis
    • Scan Tool Testing
      • All sensors should indicate the same speed
      • If all sensors do not show the same speed, carefully check the tone ring for damage
  • WHEEL SPEED SENSOR ADJUSTMENT
  • Wheel Speed Sensor Adjustment
    • Most sensors adjust by loosening a set screw and inserting a nonmagnetic brass or plastic feeler gauge between the tip of the sensor and a high point on the tone ring
  • Wheel Speed Sensor Adjustment
    • Adjust the position of the sensor so there is a slight drag on the feeler gauge, and then tighten the setscrew to lock the sensor in place
  • Wheel Speed Sensor Adjustment
    • New sensors have a piece of paper or plastic on the tip end of the unit, which must be left in place during installation to guarantee a correct air gap between the tip of the sensor and the tone ring
  • Wheel Speed Sensor Adjustment
    • Adjust the sensor so the tip just touches the tone ring and you can slip the paper or plastic out without ripping it
    • Tighten the setscrew and the air gap is properly set
  • Figure 107-13 Use a nonmagnetic brass or plastic feeler gauge to check wheel speed sensor gap. A steel gauge would be attracted by the magnet in the sensor and would produce a drag on the gauge as it is moved between the sensor and the tone ring. This drag could be interpreted as a correct clearance reading.
  • Figure 107-14 (a) Always use a nonferrous (brass or plastic) feeler (thickness) gauge when measuring the gap between the toothed ring and the wheel speed sensor.
  • Figure 107-14 (b) Sometimes a sensor is equipped with a paper spacer that is the exact thickness of the spacing required between the toothed ring and the sensor. If equipped, the sensor is simply installed with the paper touching the toothed wheel. A typical gap ranges from 0.020 to 0.050 in. (0.5 to 1.3 mm).
  • Wheel Speed Sensor Adjustment
    • Digital Wheel Speed Sensor Diagnosis
      • Check that battery voltage is available at the sensor with the key on, engine off
  • Wheel Speed Sensor Adjustment
    • Digital Wheel Speed Sensor Diagnosis
      • If the sensor does not have 12 volts, then the problem is most likely in the ABS controller or the wiring between the controller and the sensor
  • Wheel Speed Sensor Adjustment
    • Digital Wheel Speed Sensor Diagnosis
      • If there are 12 volts at the sensor, measure the signal voltage
      • The voltage should switch from about 0.8V to about 1.9V as the wheel is rotated by hand
  • OBD-II ABS DIAGNOSIS
  • OBD-II ABS Diagnosis
    • Vehicles 1996 and Newer
      • The OBD-II diagnostic connector is used to transmit ABS diagnostic trouble code information to a scan tool
  • OBD-II ABS Diagnosis
    • Vehicles 1996 and Newer
      • A factory scan tool or an enhanced factory level scan tool will be needed to retrieve ABS diagnostic trouble codes (DTCs) and scan tool data
  • OBD-II ABS Diagnosis
    • Scan Tools Needed For ABS Diagnosis
      • Scan tools can be divided into two basic groups:
        • Factory scan tools are required by all dealers that sell and service the brand of vehicle. Examples include the following:
          • General Motors —Tech 2
  • OBD-II ABS Diagnosis
    • Scan Tools Needed For ABS Diagnosis
      • Scan tools can be divided into two basic groups:
        • Factory scan tools are required by all dealers that sell and service the brand of vehicle. Examples include the following:
          • Ford —New Generation Star (NGS) and IDS (Integrated Diagnostic Software)
  • OBD-II ABS Diagnosis
    • Scan Tools Needed For ABS Diagnosis
      • Scan tools can be divided into two basic groups:
        • Factory scan tools are required by all dealers that sell and service the brand of vehicle. Examples include the following:
          • Chrysler —DRB III, Star Scan or wiTECH for CAN-equipped vehicles
  • OBD-II ABS Diagnosis
    • Scan Tools Needed For ABS Diagnosis
      • Scan tools can be divided into two basic groups:
        • Factory scan tools are required by all dealers that sell and service the brand of vehicle. Examples include the following:
          • Honda —HDS or Master Tech
  • OBD-II ABS Diagnosis
    • Scan Tools Needed For ABS Diagnosis
      • Scan tools can be divided into two basic groups:
        • Factory scan tools are required by all dealers that sell and service the brand of vehicle. Examples include the following:
          • Toyota —Techstream
  • OBD-II ABS Diagnosis
    • Scan Tools Needed For ABS Diagnosis
      • Scan tools can be divided into two basic groups:
        • Aftermarket scan tools are designed to function on more than one brand of vehicle. Examples include the following:
          • Snap-on (various models including the MT2500 and Modis) OTC (various models including Pegasus, Genisys and Task Master)
  • OBD-II ABS Diagnosis
    • Scan Tools Needed For ABS Diagnosis
      • Scan tools can be divided into two basic groups:
        • Aftermarket scan tools are designed to function on more than one brand of vehicle. Examples include the following:
          • AutoEnginuity and other programs that use a laptop or handheld computer for the display
  • OBD-II ABS Diagnosis
    • Diagnostic Procedure
      • Diagnosis steps usually include the following:
        • STEP 1: Verify the fault, making sure that it is in the antilock system and not caused by a fault in the base brakes.
  • OBD-II ABS Diagnosis
    • Diagnostic Procedure
      • Diagnosis steps usually include the following:
        • STEP 2: Retrieve any stored diagnostic trouble codes.
  • OBD-II ABS Diagnosis
    • Diagnostic Procedure
      • Diagnosis steps usually include the following:
        • STEP 3: Perform detailed tests to find the root cause.
  • OBD-II ABS Diagnosis
    • Diagnostic Procedure
      • Diagnosis steps usually include the following:
        • STEP 4: Verify the repair of the fault and clear any stored diagnostic trouble codes.
  • CHART 107–1
  • CHART 107–1 (continued)
  • CHART 107–1 (continued)
  • ABS SAFETY PRECAUTIONS
  • ABS Safety Precautions
    • Avoid mounting the antenna for the transmitting device near the ABS control unit.
    • Avoid mounting tires of different diameter than that of the original tires.
    • Never open a bleeder valve or loosen a hydraulic line while the ABS is pressurized. The accumulator must be depressurized.
  • ABS Safety Precautions
    • If arc welding on a vehicle, disconnect all computers (electronic control modules) to avoid possible damage due to voltage spikes.
    • Do not pry against or hit the wheel speed sensor ring.
  • ABS Safety Precautions
    • Quick and Easy Wheel Speed Sensor Diagnosis
      • A fault in a wheel speed sensor (WSS) is a common ABS problem
      • A quick and easy test that works on most Bosch ABS systems (and perhaps others) involves the following steps:
        • STEP 1: Hoist the vehicle safely.
  • ABS Safety Precautions
    • Quick and Easy Wheel Speed Sensor Diagnosis
      • A quick and easy test that works on most Bosch ABS systems (and perhaps others) involves the following steps:
        • STEP 2: Turn the ignition on (engine off).
  • ABS Safety Precautions
    • Quick and Easy Wheel Speed Sensor Diagnosis
      • A quick and easy test that works on most Bosch ABS systems (and perhaps others) involves the following steps:
        • STEP 3: Spin a tire by hand as fast as possible.
  • ABS Safety Precautions
    • Quick and Easy Wheel Speed Sensor Diagnosis
      • A quick and easy test that works on most Bosch ABS systems (and perhaps others) involves the following steps:
        • STEP 4: The ABS amber warning light should come on, indicating that a speed was detected but not by all the wheel speed sensors.
  • ABS Safety Precautions
    • Quick and Easy Wheel Speed Sensor Diagnosis
      • A quick and easy test that works on most Bosch ABS systems (and perhaps others) involves the following steps:
        • STEP 5: Turn the ignition off to reset the ABS warning light.
  • ABS Safety Precautions
    • Quick and Easy Wheel Speed Sensor Diagnosis
      • A quick and easy test that works on most Bosch ABS systems (and perhaps others) involves the following steps:
        • STEP 6: Repeat the test on each of the remaining wheels.
  • ABS Safety Precautions
    • If any wheel fails to turn on the ABS light, carefully inspect the wheel speed sensor for proper resistance and the tone ring and wiring
    • If the ABS light is on all the time and does not reset when the ignition is turned off, the problem is not caused by a wheel speed sensor
  • TECH TIP
    • Quick and Easy Wheel Speed Sensor Diagnosis
      • A fault in a wheel speed sensor (WSS) is a common ABS problem. A quick and easy test that works on most Bosch ABS systems (and perhaps others) involves the following steps:
    • STEP 1 Hoist the vehicle safely.
    • STEP 2 Turn the ignition on (engine off).
    • STEP 3 Spin a tire by hand as fast as possible.
    • STEP 4 The ABS amber warning light should come on, indicating that a speed was detected but not by all the wheel speed sensors.
    • STEP 5 Turn the ignition off to reset the ABS warning light.
    • STEP 6 Repeat the test on each of the remaining wheels.
    • If any wheel fails to turn on the ABS light, carefully inspect the wheel speed sensor for proper resistance and the tone ring and wiring. If the ABS light is on all the time and does not reset when the ignition is turned off, the problem is not caused by a wheel speed sensor.
    BACK TO PRESENTATION
  • FREQUENTLY ASKED QUESTION
    • What’s That Noise and Vibration?
      • Many vehicle owners and service technicians have been disturbed to hear and feel an occasional groaning noise. It is usually heard and felt through the vehicle after first being started and driven. Because it occurs when first being driven in forward or reverse, many technicians have blamed the transmission or related driveline components.
    ? BACK TO PRESENTATION
    • This is commonly heard on many ABS vehicles as part of a system check. As soon as the ABS controller senses speed from the wheel speed sensors after an ignition cycles on, the controller will run the pump either every time or whenever the accumulator pressure is below a certain level.
    • This can occur while the vehicle is being backed out of a driveway or being driven forward because wheel sensors can only detect speed—not direction. Before serious and major repairs are attempted to “cure” a noise, make sure that it is not the normal ABS self-test activation sequence of events.
  • REAL WORLD FIX
    • RWAL Diagnosis
      • The owner of an S-10 pickup truck complained that the red brake warning lamp on the dash remained on even when the parking brake was released. The problem could be one of the following:
    BACK TO PRESENTATION
      • A serious hydraulic problem
      • Low brake fluid
      • A stuck or defective parking brake switch
      • If the brake lamp is dim, RWAL trouble is indicated.
    • Checking a service manual, code 4 was found to be a grounded switch inside the hydraulic control unit. The hardest part about the repair was getting access to, and the replacement of, the defective (electrically grounded) switch. After bleeding the system and a thorough test drive, the lamp sequence and RWAL functioned correctly.
  • REAL WORLD FIX
    • The Nervous Taurus
      • A customer complained that, sometimes during normal braking, the ABS would be activated just before coming to a stop. However, the ABS light would not come on. The service technician was able to duplicate the condition and there were no DTCs stored.
    BACK TO PRESENTATION
    • Using a scan tool to monitor the wheel speed sensors, the technician discovered that the left front wheel speed was slightly different than the others. A thorough visual inspection revealed that the tone wheel (sensor ring) was cracked. This crack created a different wheel speed signal to the ABS controller than the other wheels and the controller activated the ABS as it would normally—that was why there were no DTCs.
    • Other things that could have caused this problem, which is often called “false modulation,” include a bent wheel, mismatched tire sizes, or metal debris around the sensor.
  • REAL WORLD FIX
    • The Mystery ABS Amber Warning Light
      • The owner of an Acura Legend complained to a service technician that the ABS warning light would come on but only while driving down from a parking garage.
    BACK TO PRESENTATION
    • When the driver turned off the ignition and restarted the engine, the ABS amber light was not on and did not come on again until the vehicle was again driven down the spiral parking garage ramp. The service technician used a scan tool and found that no DTCs had been stored.
      • NOTE: Some ABS systems will not retain a DTC unless the problem is currently present and the ABS amber warning light is on.
    • All of the brakes were in excellent condition, but the brake fluid level was down a little. After topping off the master cylinder with clean DOT 3 brake fluid, the vehicle was returned to the customer with the following information:
    • The ABS amber warning light may have been triggered by the brake fluid level switch. While driving down the steep parking garage ramp, the brake fluid moved away from the fluid level sensor.
        • NOTE: While the brake fluid level sensor normally would turn on the red brake warning light, in some systems it turns on the amber ABS light if the brake fluid falls below a certain level in the ABS reservoir.
      • The difference in wheel speed between the outboard and the inboard wheels could have triggered a fault code for a wheel speed sensor during the drive down the spiral parking garage ramp.
  • TECH TIP
    • Sometimes It Pays to Look at the Entire Vehicle
      • There are often strange electrical problems that can occur including false DTCs or intermittent operation of electrical sensors, ABS, accessories, or gauges. Sometimes the root of these problems is due to rust and corrosion after a vehicle is involved in a flood.
    BACK TO PRESENTATION
    • Here are some telltale signs that a vehicle may have been in a flood or in deep water.
    • Mud, silt, or caked dust under the dash and inside the doors
    • Corroded electrical connectors at the computer, fuse box, or ABS controller (computer)
    • Visible water line in the doors or behind panels
    • Rust in abnormal places such as seat springs or brackets behind the dash
    • Moisture in lenses
    • Musty smell and/or strong air freshener smell
    • Powdery corrosion on aluminum parts such as intake manifold and inside the throttle bore
    • Rust or moisture inside electrical switches or relays
    • Areas that are normally dusty such as an ashtray or glove box are very clean
  • TECH TIP
    • Space Saver Spare Tire May Trigger Wheel Speed Fault Code
      • If a vehicle has been using a small space saver-type spare tire, then the difference in outside diameter may trigger a wheel speed sensor diagnostic trouble code (DTC) and turn on the amber ABS warning lamp.
    BACK TO PRESENTATION
    • Try to find out from the customer if they had driven on a spare tire before replacing a wheel speed sensor based on a stored DTC.