Circuit/System Testing

Ignition OFF, disconnect the harness connector of the appropriate HO2S.
Ignition ON, verify that the HO2S parameter is between 350-500 mV.
- If greater than the specified value, test the signal circuit of the HO2S sensor for a short to voltage. 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 or FUEL INJECTOR BALANCE TEST WITH TECH 2 .
- Water intrusion in the HO2S harness connector
- High fuel system pressure - Refer to FUEL SYSTEM DIAGNOSIS .
- Fuel that is contaminated - Refer to ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS (W/O SPECIAL TOOL) and ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS (W/ SPECIAL TOOL) .
- Fuel saturation of the evaporative emissions (EVAP) canister
- Restricted exhaust
- Contaminated HO2S - Silicon
  - If you find any of the above conditions, repair as necessary.
If all circuits/connections test normal, replace the applicable HO2S.