The engine main relay is a normally open relay. The relay switch is held in the open position by spring tension. Battery positive voltage is supplied directly to the relay coil and the relay switch contact at all times. The powertrain control module (PCM) supplies the ground path to the relay coil control circuit through an output driver module (ODM). The ODM for the engine main relay also incorporates a fault detection circuit, which is continuously monitored by the PCM. The ignition 1 voltage that is supplied to the PCM through the ETC fuse provides power to the internal PCM circuits associated with the throttle actuator control (TAC) operation. The PCM also monitors the voltage level on the ignition 1 voltage circuit to confirm that the engine main relay contacts have closed.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Electrical Information Reference

Scan Tool Reference

1. Ignition OFF, disconnect the engine main relay.
2. Ignition ON, verify that a test lamp illuminates between the engine main relay coil B+ and ground.

⇒	If the lamp does not illuminate, test the B+ circuit for a short to ground or an open/high resistance. If the circuit tests normal, test or replace the battery positive cable to the underhood fuse block.

3. Ignition OFF, verify that a test lamp does not illuminate between the engine main relay coil B+ circuit and the control circuit.

⇒	If the test lamp illuminates, test the control circuit for a short to ground. If the circuit tests normal, replace the PCM.

4. Remove the test lamp.
5. Ignition ON, verify with a scan tool that the engine main relay EC Ignition Relay Circuit Status parameter is OK.

⇒	If not the specified value, test the control circuit for a short to voltage. If the circuit tests normal, replace the PCM.

6. Test the coil side of the engine main relay for 65-110 ohms.

⇒	If not within the specified value, replace the relay.

7. Ignition OFF, disconnect the PCM C1 connector.
8. Test the engine main relay control circuit for an open/high resistance.

⇒	If the circuit tests normal, replace the PCM.

9. Verify that a test lamp does not illuminate between the relay ignition 1 voltage circuit at the engine main relay and ground.

⇒	If the test lamp illuminates, test the relay ignition 1 voltage circuit for a short to voltage between the engine main relay and each component powered by the relay.

10. Verify that a test lamp illuminates between the relay switch B+ and ground.

⇒	If the test lamp does not illuminate, test the relay switch B+ circuit for a short to ground, or an open/high resistance. If the circuits test normal, and the fuse for the ignition 1 voltage circuit is open, test the ignition 1 voltage circuit for a short to ground.

11. Connect a 20A fused jumper wire between the relay switch B+ and the relay ignition 1 voltage circuit.
12. Ignition ON, engine OFF, probe the ignition voltage circuit for each component powered by the engine main relay.

⇒	If the test lamp does not illuminate, test the ignition 1 voltage circuit for an open/high resistance.

⇒	If all circuits test normal, replace the relay.

1. Install any components that have been removed or replaced during diagnosis.
2. Perform any adjustment, programming, or setup procedures that are required when a component or module is removed or replaced.
3. Clear the DTCs.
4. Turn OFF the ignition for 60 seconds.
5. Ignition ON, observe the circuit status parameters for each component powered by the engine main relay. The circuit status parameters should indicate OK.
6. Start the engine. If the engine does not run, refer to Engine Cranks But Does Not Run .
7. If another DTC is present, perform the appropriate diagnostic procedure.