Circuit/System Testing

Ignition OFF, disconnect the harness connector at the appropriate HO2S.
Ignition ON, test for less than 0.1 volt between the low reference circuit terminal 1 and ground.
- If greater than the specified range, test the low reference circuit for a short to voltage. If the circuit tests normal, replace the ECM.
Ignition ON, verify the scan tool HO2S parameter is between 350-500 mV.
- If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
Verify the following conditions do not exist:
- Water intrusion in the HO2S harness connector
- High fuel system pressure-Refer to Fuel System Diagnosis .
- Rich fuel injectors or fuel injectors that are leaking-Refer to Fuel Injector Balance Test with Special Tool .
- Fuel saturation of the evaporative emission (EVAP) canister
- Exhaust system restrictions
- Leaking fuel pressure regulator-Inspect for evidence of fuel in the vacuum line. Refer to Fuel System Diagnosis .
- If you find any of the above conditions, repair as necessary.
If all circuits test normal, test or replace the applicable HO2S.