Circuit/System Testing

Ignition OFF, disconnect the harness connector of the HO2S 1.
Ignition ON, verify that the HO2S 1 parameter is between 350-500 mV.
- If greater than 500 mV, test the signal circuit of the HO2S sensor 1 for a short to voltage. If the circuit/connections test normal, replace the engine control module (ECM).

IMPORTANT: The test lamp is used to load the circuit and may not illuminate.

Connect a test lamp between the low reference circuit of the HO2S sensor 1 and B+.
Ignition ON, test for less than 0.1 volt between the low reference circuit of the HO2S sensor 1 and ground.
- If greater than 0.1 volt, test the low reference circuit of the HO2S sensor 1 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 Electronic Ignition (EI) System 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 HO2S sensor 1.