Circuit/System Testing

Ignition OFF, disconnect the harness connector at the HO2S 1.
Ignition OFF, test for less than 5 ohms of resistance between the low reference circuit terminal 3 and ground.
- If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
Ignition ON, verify the scan tool HO2S 1 parameter is between 350-500 mV.
- If less than the specified range, test the signal circuit for a short to ground. If the circuit tests normal, replace the ECM.
- If greater than the specified range, test the signal circuit for a short to voltage. If the circuit tests normal, replace the ECM.
Install a 3A fused jumper wire between the signal circuit terminal 1 and the low reference circuit terminal 3. Verify the scan tool HO2S 1 parameter is less than 60 mV.
- If greater than the specified range, test the signal circuit for an open/high resistance. If the circuit tests normal, replace the ECM.
Verify 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 .
- 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 test normal, test or replace the HO2S.