Advanced Emission Diagnostic Training

Module IIIModule 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

Advanced Emission Diagnostic Training

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

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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

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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.

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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

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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

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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

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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

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Serial data Information is transmitted through a wire

as a code Information is transmitted from 1

complete cycle Repeated constantly

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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

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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

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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

Advanced Emission Diagnostic Training

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