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.

The ECM detects the Engine Controls Ignition Relay Control Circuit is open, shorted to ground, or shorted to voltage.

DTC P0685 is a Type C DTC.

DTC P0685 is a Type C DTC.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Important: If You were sent here from Engine Cranks But Does Not Run proceed to Circuit/System Testing.

1. Ignition ON, observe the DTC information with a scan tool. DTC P0685 should not set.
2. Cycle the ignition from OFF to ON. You should hear and feel an audible click from the EC ignition relay. Repeat as necessary in order to verify EC ignition relay operation.
3. 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 List.

1. Ignition OFF, disconnect the EC ignition relay.
2. Ignition ON, verify that a test lamp illuminates between the coil voltage supply circuit 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 and the coil voltage supply circuit.

⇒	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.

Important: The ignition 1 voltage circuit is between the EC ignition relay and the ECM. The ignition 1 voltage is a feedback circuit.

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

⇒	If the engine does not start, test the ignition 1 voltage circuit between the EC ignition 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 EC ignition relay.

1. Measure for 70-110 ohms of resistance between terminals 85 and 86 of the EC ignition relay.

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

2. Measure for infinite resistance between the following terminals of the EC ignition relay:

•

30 and 86

•

30 and 87

•

30 and 85

•

85 and 87

⇒	If continuity is detected, replace the EC ignition relay.

3. Connect a 20A fused jumper wire from B+ to relay terminal 85. Connect a jumper wire from ground to relay terminal 86. Measure for less than 2 ohms between terminals 30 and 87 of the relay.

⇒	If the resistance measures greater than 2 ohms, replace the EC ignition relay.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.