Circuit/System Testing

Ignition OFF, disconnect the harness connector at the appropriate HO2S sensor.
Ignition ON, verify the scan tool HO2S voltage parameter is between 350-500 mV.
- If less than the specified value, test the signal circuit for a short to ground. If the circuit/connections test normal, replace the ECM.
- If greater than the specified value, test the signal circuit for a short to voltage. If the circuit/connections test normal, replace the ECM.
Install a 3A fused jumper wire between the signal circuit terminal B and ground. Verify the scan tool HO2S voltage 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.
Connect a 3A fused jumper wire between the signal circuit terminal B and the low reference circuit terminal A. Verify the scan tool HO2S voltage parameter is less than 60 mV.
- If greater than the specified value, test the low reference circuit for an open/high resistance or for a short to voltage. If the circuit/connections test normal, replace the ECM.
Verify that the following conditions do not exist:
- Leaking fuel injectors-Refer to FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL or FUEL INJECTOR BALANCE TEST WITH TECH 2 .
- 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) .
- Restricted exhaust.
  - If you find any of the above conditions, repair as necessary.
If all circuits/connections test normal, replace the HO2S sensor.