This document summarizes the goals and key points of Module III which covers oxygen sensors, scopes, and oxygen sensor testing and analysis. The main topics are: 1) The different types of oxygen sensors including heated, unheated, titania, and zirconium sensors and how they react to exhaust oxygen levels. 2) How zirconium and titania sensors produce a voltage signal in response to exhaust oxygen levels. 3) How to set up an analog or digital scope to analyze oxygen sensor waveforms and the characteristics of different types of electrical signals. 4) The criteria for a good oxygen sensor including minimum and maximum voltage levels and switching frequency.

1.  Module III
Module goals
 Various types of 02 sensors
 Analog and digital scopes
 Scope set-up to analyze 02 sensor wave form
 Four types of electrical signals
 Three characteristics of electrical signals
 02 sensor tests & analysis

2.  02 sensor is an input to the PCM
 Different types
 Heated
 Unheated
 Titania
 Zirconium
 They react to the amount of oxygen left over after
combustion in the exhaust

3.  Zirconium sensors
 Compares exhaust 02 to ambient air 02 and produces a voltage
 .1 to .9
 Most common
 Titania sensor
 1 volt signal to sensor
 Thermistor
 Jeep -- renix feedback system
 5 volt reference
 Thermistor
 Leaner the exhaust = heat = low voltage
 All produce the same wave form
 Will need different voltage scale

4.  A good 02 sensor
 Minimum voltage should be below .175
 Maximum voltage should be above .800
 A feed back system must go rich then lean for
the cat. to function properly.

5. Analog scope
 CRT display
 Real time
 What you see is what you are measuring
 Hard to find a glitch
 Less portable
 Less adjustable
Digital scope
 CRT or LCD display
 Scope reads signal
 Stores signal
 Displays signal
 Has adjustable sampling rate & voltage
 Storage & recall

6.  Scopes display voltage over time
 Most DSO scopes will set voltage & time for
the sensor selected
 If you have to set the scope
 Set it to display at least one complete cycle

7.  DC voltage
 Straight line
 Height indicates voltage level
 Sources are battery voltage or off-on switch
 Will be curved if time base is set properly and voltage
varies.
 AC voltage
 Signal goes above and below 0 line
 wave form can be pointed
 May not be sinusoidal
 Equal above & below 0 line
 ABS and magnetic pick-up’s

8.  Pulse train -- signals vary by:
 Frequency
 How many cycles repeat itself in a second
 Duty cycle
 Percent of ON time compared to OFF time in one cycle
 Pulse width
 Measurement of ON time only
 Measured in ms

9.  Serial data
 Information is transmitted through a wire as a
code
 Information is transmitted from 1 complete
cycle
 Repeated constantly

10.  Characteristics of wave forms
 Amplitude = total range of voltage
 Frequency = how fast a cycle is repeated in 1
second
 Sequence of events = combinations of on/off
cycles, like Morse Code

11.  02 sensor test
 A good 02 sensor will
 Raise to .800 volts
 Drop to .175 volts
 Min to max in less than 100ms
 Read steps 1 thru 5 on page 3-21

12.  A good 02 sensor wave form will look like the
graph on page 3-22.
 It MUST switch above and below .45 volts 1
time every 2 seconds up to 5 times a second
 This sets up a TWC to function as it was
designed

13.  Please NOTE an 02 sensor that does not report
the 02 content of the exhaust, or reports it too
slow (partial switching) will not furnish the
information to the PCM to control fuel delivery
as designed