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