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VVC AUTO 85.5 - Smog Technician - Level 1 - O2 sensor _waveform_characteristics
 

VVC AUTO 85.5 - Smog Technician - Level 1 - O2 sensor _waveform_characteristics

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    VVC AUTO 85.5 - Smog Technician - Level 1 - O2 sensor _waveform_characteristics VVC AUTO 85.5 - Smog Technician - Level 1 - O2 sensor _waveform_characteristics Presentation Transcript

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