Introduction to On Board Diagnostics (II)

Fundamentals of PowertrainControl strategies & OBD IIDiagnosticsThe desired voltage is displayed on the Instrument panel (IP) in multiples of 1/100 volt.Thus to say , “00” corresponds to 0 volts and “99” corresponds to 0.99 volt, etc.Using this voltage, the mechanic follows the following procedure: If the O sensor 2 voltageis less than 0.37volt and more than 0.57 volt, the mechanic is directed by the procedureto investigate the circuit wiring of the O 2 sensor for defects.If the O sensor 2 voltage is between 0.37 volt and 0.57 volt tests are performedto determine whether O sensor or the control (circuit) unit processing the O 2 2 sensor signalis faulty.The mechanic can then jumper the input leads together at the input to the control unit,simulating a O 2 sensor short circuit, and must read the sensor voltage value using theOBD II display procedure. If this voltage is less than 0.05 volt, the control unit isfunctioning correctly and the O 2 sensor must be investigated for defects. If the indicatedsensor voltage is greater than 0.05 volt, the control unit is faulty and should be replaced.when diagnosing a problem, the mechanic might wish to clear a fault code from the PCMmemory. A good reason to do this can be to test whether the failure is “hard” orintermittent. To clear DTC the mechanic pushes “OFF” and “HI” buttons on IPsimultaneously until “00” is displayed on IP.