Circuit/System Testing
- Ignition OFF, disconnect the harness connector of the HO2S.
- Ignition ON, verify that the HO2S parameter is between 350-500 mV.
- If less than 350 mV, test the signal circuit of the HO2S sensor for a short to ground. If the circuit/connections test normal, replace the engine control module (ECM).
- Connect a test lamp between the low reference circuit of the HO2S sensor and the positive battery terminal.
- Ignition ON, test for less than 0.1 volt between the low reference circuit of the HO2S sensor and the negative terminal of the battery.
- If greater than 0.1 volt, test the low reference circuit of the HO2S for a short to voltage or an open/high resistance. If the circuit/connections test normal, replace the ECM.
- Install a 3-amp fused jumper wire between the signal circuit and the low reference circuit of the HO2S sensor and verify the HO2S sensor parameter is less than 60 mV.
- If greater than 60 mV, test the signal circuit of the HO2S sensor for an open/high resistance. If the circuit/connections test normal, replace the ECM.
- Verify that the following conditions do not exist:
- Lean fuel injectors-Refer to Fuel Injector Balance Test with Special Tool .
- Low fuel system pressure-Refer to Fuel System Diagnosis .
- Fuel that is contaminated
- Exhaust leaks near the HO2S
- Engine vacuum leaks
- If you find any of the above conditions, repair as necessary.
- If all circuits/connections test normal, replace the applicable HO2S.
IMPORTANT:
The test lamp is used to load the circuit and may not illuminate.