Circuit Description

PCM supplies a bias voltage (about 450 mV) on HO2S high and low signal circuits. Oxygen sensor voltage ranges from 10 mV when exhaust is lean to 1000 mV when exhaust is rich. PCM monitors and stores HO2S voltage information. PCM then evaluates voltage samples to determine amount of time HO2S voltage was out of range. PCM will compare stored HO2S voltage samples taken each sample period and determine if majority of samples are out of operating range. If PCM detects that voltage is out of bias range, DTC will set.

For duplication of DTC, ensure:

• DTCs P0101, P0102, P0103, P0112, P0113, P0117, P0118, P0121, P0122, P0123, P0125, P0200, P0335, P0336, P0351-P0358 or P1258 are not set.
• Ignition voltage is greater than 9 volts.
• Fuel system is operating in closed-loop.
• AIR, EGR and catalyst diagnostics are not active.
• Engine run time is more than 70 seconds.