Circuit/System Testing
- Ignition OFF, disconnect the harness connector at the appropriate HO2S.
- Ignition ON, verify that a test lamp illuminates between the ignition 1 voltage circuit terminal 4 and ground.
- If the test lamp does not illuminate, test the ignition 1 voltage circuit for a short to ground or an open/high resistance. If the circuit tests normal and the ignition 1 voltage circuit fuse is open, test all components connected to the ignition 1 voltage circuit and replace as necessary.
- Ignition OFF, connect a test lamp between the control circuit and 12 volts. The test lamp should not illuminate.
- HO2S (EURO IV) heater control circuit terminal 2
- HO2S (Non EURO IV) heater control circuit terminal 3
- If test lamp is always ON, test the control circuit for a short to ground. If the circuit tests normal, replace the ECM.
- Engine running, verify the test lamp illuminates or flashes.
- If the test lamp is always OFF, test the control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.
- If all circuits test normal, test or replace the HO2S sensor.