The Engine Controls Ignition Relay or Main Relay, is controlled by the engine control module (ECM) depending upon input from the ignition switch. Battery positive voltage is supplied to the relay coil and switch. When the ignition switch is turned to the ON position, the ECM will provide ground on the control circuit of the relay using a low side driver. This will allow voltage through the relay switch contacts to the components. The ECM monitors the voltage level on the control circuit of the relay.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Electrical Information Reference

Scan Tool Reference

Special Tools Required

J 43244 Relay Puller Pliers

Cycle the ignition from OFF to ON. You should hear and feel an audible click from the main relay. Repeat as necessary in order to verify main relay operation.

1. Ignition OFF, disconnect the main relay.
2. Ignition ON, verify a test lamp illuminates between the coil voltage supply circuit terminal 86 and ground.

⇒	If the test lamp does not illuminate, repair the coil voltage supply circuit for a short to ground or an open/high resistance.

3. Ignition OFF, connect a test lamp between the coil control circuit terminal 85 and the coil voltage supply circuit terminal 86.

⇒	If the test lamp remains ON all the time, test for a short to ground on the control circuit. If the circuit/connections test normal, replace the ECM.

4. Ignition ON, the test lamp should turn ON.

⇒	If the test lamp remains OFF all the time, test for a short to voltage or an open/high resistance on the control circuit. If circuit/connections test normal, replace the ECM.

5. Connect a 15A fused jumper wire between the switch voltage supply circuit terminal 30 and the ignition 1 voltage circuit terminal 87.
6. Attempt to start the engine. The engine should start.

⇒	If the engine does not start, test the ignition 1 voltage circuit between the main relay and the ECM for a short to ground or for an open/high resistance. If the circuit/connections test normal, replace the ECM.

7. If all circuits/connections test normal, test or replace the main relay.

1. Test for 70-110 ohms of resistance between terminals 85 and 86.

⇒	If not within the specified range, replace the main relay.

2. Test for infinite resistance between the following terminals:

•

30 and 86

•

30 and 87

•

30 and 85

•

85 and 87

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

3. Connect a 20A fused jumper wire from the positive terminal of the battery to relay terminal 85. Connect a jumper wire from the negative terminal of the battery to relay terminal 86. Test for less than 2 ohms of resistance between terminals 30 and 87.

⇒	If more than the specified range, replace the main relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.