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 provides an overview of each diagnostic category.

### DTC Descriptors

DTC P0683: Glow Plug Control Module Communication Circuit
DTC P0683 3A: Incorrect Component Installed
DTC P0683 71: Invalid Serial Data Received

### Circuit/System Description

The glow plug control module monitors the glow plugs, and control circuits for faults. This information is communicated to the engine control module (ECM) over a discrete communication circuit.

### Conditions for Running the DTC

• | The ignition is ON, or the engine is running.

• | The ignition voltage is greater than 9 volts.

• | The DTCs run continuously once the above conditions are met.

### Conditions for Setting the DTC

#### P0683 3A

The ECM detects a glow plug control module hardware mismatch.

#### P0683 71

The ECM detects an invalid signal from the glow plug control module.

### Action Taken When the DTC Sets

DTCs P0683 3A and P0683 71 are Type C DTCs.

### Conditions for Clearing the DTC

DTCs P0683 3A and P0683 71 are Type C DTCs.

### Reference Information

#### Schematic Reference

Engine Controls Schematics

#### Connector End View Reference

Component 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

Control Module References for scan tool information

### Circuit/System Verification

1. Ignition ON, observe the DTC information with a scan tool. DTCs P0683 3A or P0683 71 should not set.

⇒ | If DTC P0683 3A is set, replace the glow plug control module.

2. 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.

### Circuit/System Testing

1. Ignition OFF, and the MAIN fuse removed, disconnect the harness connector at the glow plug control module.
2. Test for less than 5 ohms between the glow plug control module ground circuit terminal 7 and ground.

⇒ | If greater than the specified range, repair the ground circuit for an open/high resistance.

3. Install the MAIN fuse. Ignition ON, verify a test lamp illuminates between the ignition 1 voltage circuit terminal 6 and ground.

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

4. Test for greater than 10 volts between the glow plug control module control circuit terminal 10 and ground.

⇒ | If less than the specified range, test the control circuit for an open or a short to ground. If the circuit tests normal, replace the ECM.

5. Test for greater than 10 volts between the glow plug control module communication circuit terminal 9 and ground.

⇒ | If less than the specified range, test the communication circuit for an open or a short to ground. If the circuit tests normal, replace the ECM.

6. Test the DC frequency from the glow plug control module control circuit terminal 10. Command the glow plug control module ON with a scan tool. Verify the DC frequency is between 30-35 Hz.

⇒ | If less than the specified range, test the control circuit for a short to voltage. If the circuit tests normal, replace the ECM.

⇒ | If greater than the specified range, test the control circuit for a high resistance. If the circuit tests normal, replace the ECM.

7. Test the AC frequency from the glow plug control module communication circuit terminal 9. Command the glow plug control module ON with a scan tool. Verify the AC frequency is between 30-35 Hz.

⇒ | If less than the specified range, test the communication circuit for a short to voltage. If the circuit tests normal, replace the ECM.

⇒ | If greater than the specified range, test the communication circuit for a high resistance. If the circuit tests normal, replace the ECM.

8. If all circuits test normal, test or replace the glow plug control module.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Glow Plug Replacement

• | Control Module References for ECM setup and programming