vvc auto 85.5 - smog technician - level 1 - o2 sensor _waveform_characteristics
Post on 19-Oct-2014
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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
Advanced Emission Diagnostic Training
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
Advanced Emission Diagnostic Training
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.
Advanced Emission Diagnostic Training
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
Advanced Emission Diagnostic Training
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
Advanced Emission Diagnostic Training
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
Advanced Emission Diagnostic Training
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
Advanced Emission Diagnostic Training
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