Circuit/System Testing

Ignition OFF, disconnect the harness connector of the applicable HO2S.
Ignition ON, verify that the applicable HO2S 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 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 ECM.
Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit and ground.
- If greater than the specified value, test the low reference circuit for a short to voltage or an open/high resistance. If the circuit/connections test normal, replace the ECM.
Install a 3A fused jumper wire between the signal circuit and the low reference circuit. Engine idling, verify the HO2S parameter is less than 60 mV.
- If greater than the specified value, test the signal circuit 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 applicable HO2S.