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 less than 350 mV, test the signal circuit of the HO2S sensor 1 for a short to ground. If the circuit/connections test normal, replace the ECM.
Verify that none of the following conditions exist:
- Lean fuel injectors-Refer to Fuel Injector Balance Test with Special Tool .
- Water intrusion in the HO2S harness connector.
- Low 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) .
- Exhaust leaks near the HO2S
- Contaminated HO2S-Silicon
- Engine vacuum leaks
- If you find any of the above conditions, repair as necessary.
If all circuits/connections test normal, replace the HO2S sensor 1.