Circuit/System Testing

Verify that none of the following conditions exist:
- Lean 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
- 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.
Ignition OFF, disconnect the harness connector of the appropriate HO2S 2.
Ignition ON, verify the appropriate scan tool HO2S 2 voltage parameter is between 350-550 mV.
- If less than the specified range, test the signal circuit for a short to ground. If the circuit/connections test normal, replace the ECM.
Connect the harness connector at the HO2S 2.
Engine idling, raise the engine speed above 1,200 RPM for 30 seconds. Verify the appropriate scan tool HO2S 2 voltage parameter is greater than 60 mV.
- If less than the specified value, replace the HO2S 2.
Engine idling, move the appropriate HO2S 1 and HO2S 2 harnesses between the HO2S harness connectors and the ECM. Observe the appropriate scan tool HO2S 1 voltage parameter, and the HO2S 2 voltage parameter.
- If a parameter changes abruptly, repair the harness/connections as necessary.
If all circuits/connections test normal, replace the applicable HO2S 1.