Diagnostic Aids

If DTC P0141 is also present, diagnose this DTC first. An inoperative heater may cause the sensor to cool down, causing DTC to set. PCM will not perform a catalyst monitor test if DTC P0140 is present.

Use scan tool to review malfunction history diagnostic information. This data can be used to duplicate a problem. Check tightness of harness connector terminals. Normal scan tool readings in closed loop will show the oxygen sensor voltage varying between 100 mV and 999 mV. DTC can set or cause false oxygen sensor readings if the oxygen sensor ground is loose.