Circuit/System Testing

Ignition OFF, disconnect the harness connector of the appropriate HO2S.
Engine idling, verify that the HO2S parameter is between 350-500 mV.
- If greater than 500 mV, test the signal circuit for a short to voltage. If the circuit/connections test normal, replace the ECM.
Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit and ground.
- If greater than 5 ohms, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit/connections test normal, replace the ECM.
Verify that none of the following conditions exist:
- Rich fuel injectors. Refer to Fuel Injector Balance Test with Special Tool .
- Water intrusion in the HO2S harness connector
- High fuel system pressure. Refer to Fuel System Diagnosis .
- Fuel that is contaminated. Refer to Alcohol/Contaminants-in-Fuel Diagnosis .
- Fuel saturation of the evaporative emission (EVAP) canister
- Exhaust leaks near the HO2S
- Contaminated HO2S-Silicon
- If you find any of the above conditions, repair as necessary.
If all circuits/connections test normal, replace the applicable HO2S.