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

### Conditions for Clearing the DTC

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

### 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

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. DTC P0671, P0672, P0673, or P0674 should not set.

### Circuit/System Testing

1. Ignition OFF, and the MAIN fuse removed, disconnect the harness connector at the glow plug control module.
2. Test for 1-2.5 ohms of resistance between the appropriate glow plug control circuit terminal and ground.

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

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

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

### Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Glow Plug Replacement