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 P0671 02: Cylinder 1 Glow Plug Control Circuit Short to Ground
DTC P0671 04: Cylinder 1 Glow Plug Control Circuit Open Circuit
DTC P0672 02: Cylinder 2 Glow Plug Control Circuit Short to Ground
DTC P0672 04: Cylinder 2 Glow Plug Control Circuit Open Circuit
DTC P0673 02: Cylinder 3 Glow Plug Control Circuit Short to Ground
DTC P0673 04: Cylinder 3 Glow Plug Control Circuit Open Circuit
DTC P0674 02: Cylinder 4 Glow Plug Control Circuit Short to Ground
DTC P0674 04: Cylinder 4 Glow Plug Control Circuit Open Circuit

### Circuit/System Description

The glow plug controller is a solid state device which operates the glow plugs. The temperature and the power consumption is controlled between the engine control module (ECM) and the glow plug controller within a wide range to suit the engine's pre-heating requirements. The ECM controls the glow plug module with a pulse-width modulated (PWM) control circuit. The glow plug initial ON time will vary based on the system voltage and temperature. Lower temperatures cause longer ON times.

### Conditions for Running the DTC

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

• | The ignition voltage is less than 16 volts.

• | The DTCs run once per ignition cycle when the above conditions are met.

### Conditions for Setting the DTC

The ECM detects an open or a short to ground on a glow plug control circuit for greater than 6 seconds.

### Action Taken When the DTC Sets

DTC P0671, P0672, P0673, P0674 are Type C DTCs.

### Conditions for Clearing the DTC

DTC P0671, P0672, P0673, P0674 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. DTC P0671, P0672, P0673, or P0674 should not set.
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 K38 glow plug control module.
2. Test for 1-2.5 Ω between the appropriate glow plug control circuit terminal and ground.

⇒ | If less than the specified range, test the control circuit for a short to ground. If the circuit tests normal, replace the E12 Glow Plug.

⇒ | If greater than the specified range, test the control circuit for an open/high resistance. If the circuit tests normal, replace the E12 Glow Plug.

3. If all circuits test normal, test or replace the K38 glow plug control module.

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

• | Glow Plug Replacement

• | Glow Plug Controller Replacement