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 B DTC.

DTC P0685 is a Type B DTC.

Schematic Reference

Engine Controls Schematics

Connector End View Reference

Component Connector End Views

Electrical Information Reference

DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

Scan Tool Reference

Control Module References for scan tool information

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. Operate the vehicle within the Conditions for Running the DTC to verify the DTC does not reset. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

1. Ignition OFF, disconnect the EC ignition relay.
2. Ignition ON, verify a test lamp illuminates between the relay coil B+ circuit terminal 85 and ground.

⇒	If the test lamp does not illuminate, repair the relay coil ignition 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 86 and the relay coil B+ circuit terminal 85.

⇒	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.

4. Ignition ON, verify the test lamp turns ON.

⇒	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.

5. Ignition ON, verify a test lamp illuminates between the relay switch B+ voltage circuit terminal 30 and ground.

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

Important: The relay switch controlled output circuit is between the EC ignition relay and the ECM. The relay switch controlled output circuit is a feedback circuit.

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

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

8. If all circuits test normal, test or replace the EC ignition relay.

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

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

Control Module References for ECM replacement, setup, and programming