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

Component Connector End Views

Electrical Information Reference

Scan Tool Reference

Control Module References for scan tool information

Special Tools

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 relay coil ignition 1 voltage circuit terminal 86 and ground.

⇒	If the test lamp does not illuminate, repair the relay coil ignition 1 voltage circuit for a short to ground or an open/high resistance.

3. Ignition OFF, connect a test lamp between the relay coil control circuit terminal 85 and the relay coil ignition 1 voltage circuit terminal 86.

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

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

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

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

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

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

1. Ignition OFF, disconnect the main relay.
2. Test for 70-110 ohms between terminals 85 and 86.

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

3. 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.

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 2 ohms between terminals 30 and 87.

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

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.