Circuit/System Testing

Ignition OFF, disconnect the harness connector of the heated oxygen sensor (HO2S) 2.
Ignition ON, verify that the HO2S 2 parameter is between 350-500 mV.
- If less than 350 mV, test the signal circuit of the HO2S for a short to ground. If the circuit/connections test normal, replace the engine control module (ECM).
- If greater than 500 mV, test the signal circuit of the HO2S 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 and B+.
Ignition ON, test for less than 0.1 volt between the low reference circuit of the HO2S and ground.
- If greater than 0.1 volt, test the low reference circuit of the HO2S for a short to voltage or an open/high resistance. If the circuit/connections test normal, replace the ECM.
Install a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the HO2S and verify the appropriate HO2S parameter is less than 60 mV.
- If greater than 60 mV, test the signal circuit of the HO2S for an open/high resistance. If the circuit/connections test normal, replace the ECM.
Verify that none of the following conditions exist:
- Lean or rich fuel injectors-Refer to Fuel Injector Balance Test with Special Tool .
- Water intrusion in the HO2S harness connector.
- Low or high fuel system pressure-Refer to Fuel System Diagnosis .
- Fuel that is contaminated-Refer to Alcohol/Contaminants-in-Fuel Diagnosis (w/o Special Tool) or Alcohol/Contaminants-in-Fuel Diagnosis (w/Special tool) .
- Fuel saturation of the evaporative emission (EVAP) canister.
- Exhaust leaks near the HO2S.
- Engine vacuum leaks.
- If you find any of the above conditions, repair as necessary.
If all circuits/connections test normal, replace the HO2S.