For 1990-2009 cars

### Diagnostic Instructions

• | Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• | Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• | Diagnostic Procedure Instructions provide an overview of each diagnostic category.

### DTC Descriptor

DTC P0685: Engine Controls Ignition Relay Control Circuit

### Circuit/System Description

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.

### Conditions for Running the DTC

• | The ignition is ON or the engine is operating.

• | The ignition voltage is between 7.5-16 volts.

• | The DTC runs continuously once the above conditions are met.

### Conditions for Setting the DTC

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

### Action Taken When the DTC Sets

DTC P0685 is a Type C DTC.

### Conditions for Clearing the DTC

DTC P0685 is a Type C DTC.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

• | Engine Control Module Connector End Views

• | Engine Controls Connector End Views

#### Electrical Information Reference

• | Circuit Testing

• | Connector Repairs

• | Testing for Intermittent Conditions and Poor Connections

• | Wiring Repairs

#### DTC Type Reference

Powertrain Diagnostic Trouble Code (DTC) Type Definitions

#### Scan Tool Reference

• | Scan Tool Data List

• | Scan Tool Data Definitions

• | Scan Tool Output Controls

### Circuit/System Verification

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.

### Circuit/System Testing

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.

### Component Testing

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.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Relay Replacement

• | Control Module References for ECM replacement, setup, and programming