The main relay is a normally open relay. The relay armature is held in the open position by spring tension. Battery positive voltage is supplied directly to the relay coil and the armature contact at all times. The engine control module (ECM) supplies the ground path to the relay coil control circuit via an internal integrated circuit called an output driver module (ODM). The ODM output control is configured to operate as a low side driver for the main relay. The ODM for the main relay also incorporates a fault detection circuit, which is continuously monitored by the ECM. When the ECM commands the main relay ON, ignition 1 voltage is supplied to several circuits.

This test procedure requires that the vehicle battery has passed a load test and is completely charged. Refer to Battery Inspection/Test .

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Electrical Information Reference

Scan Tool Reference

Special Tools Required

Important: On the scan tool, the main relay is referred to as the EC ignition relay.

1. Ignition ON, engine OFF, command the main relay ON and OFF several times using the scan tool output control function. You should either hear or feel the relay click with each command.
2. Ignition ON, engine OFF, with a test lamp, probe both test points of all of the fuses that are powered by the main relay. The test lamp should illuminate on at least one test point of each fuse.

⇒	If the vehicle passes the Circuit/System Verification Test, then operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that are captured in the Freeze Frame/Failure Records Data list.

1. Ignition OFF, disconnect the main relay.
2. Ignition ON, verify that a test lamp does not illuminate between the relay coil control circuit terminal R50 and ground.

⇒	If the test lamp illuminates, test the relay coil control circuit for a short to voltage. If the circuit tests normal, replace the ECM.

3. Verify that a test lamp does not illuminate between the relay ignition 1 voltage circuit terminal R49 and ground.

⇒	If the test lamp illuminates, test the relay ignition 1 voltage circuit for a short to voltage. If the circuit tests normal, replace the ECM.

4. Verify that a test lamp illuminates between the relay coil B+ terminal R47 and ground.

⇒	If the test lamp does not illuminate, test the relay coil B+ circuit for a short to ground or an open/high resistance.

5. Verify that a test lamp illuminates between the relay switch B+ terminal R48 and ground.

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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 to the ECM for a short to ground. If the circuit tests normal, replace the ECM.

6. Connect a test lamp between the relay coil B+ terminal R47 and the relay coil control circuit terminal R50.
7. Ignition ON, command the main relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the relay coil control circuit for a short to ground. If the circuit tests normal, replace the ECM.

⇒	If the test lamp is always OFF, test the relay coil control circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the ECM.

8. Connect a 20A fused jumper wire between the relay switch B+ terminal R48 and the relay ignition 1 voltage circuit terminal R49.
9. Ignition ON, engine OFF, monitor the EC Ignition Relay Feedback parameter with a scan tool. The parameter should display B+.

⇒	If the parameter does not display B+, test the ignition 1 voltage circuit for an open/high resistance. If the circuit tests normal, replace the ECM.

10. If all circuits test normal, test or replace the relay.

1. Ignition OFF, disconnect the main relay.
2. Test for 65-110 ohms of resistance between terminals 85 and 86 of the relay.

⇒	If the resistance is not within the specified range, replace the relay.

3. Test for infinite resistance between the following terminals:

•	Terminal 30 and 86

•	Terminal 30 and 87

•	Terminal 30 and 85

•	Terminal 85 and 87

⇒	If not the specified value, replace the relay.

4. Install a 20A fused jumper wire between relay terminal 85 and 12 volts. Install a jumper wire between relay terminal 86 and ground. Test for less than 1 ohm of resistance between terminals 30 and 87.

⇒	If greater than the specified range, replace the relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.