Diagnostic Instructions

DTC Descriptors

DTC  P0671: Cylinder #1 Glow Plug Control Circuit

DTC  P0672: Cylinder #2 Glow Plug Control Circuit

DTC  P0673: Cylinder #3 Glow Plug Control Circuit

DTC  P0674: Cylinder #4 Glow Plug Control Circuit

DTC  P0675: Cylinder #5 Glow Plug Control Circuit

DTC  P0676: Cylinder #6 Glow Plug Control Circuit

DTC  P0677: Cylinder #7 Glow Plug Control Circuit

DTC  P0678: Cylinder #8 Glow Plug Control Circuit

Diagnostic Fault Information

Circuit	Short to Ground	High Resistance	Open	Short to Voltage	Signal Performance
Glow Plug 1 Control Circuit	P0671	P0671	P0671	P0671	--
Glow Plug 2 Control Circuit	P0672	P0672	P0672	P0672	--
Glow Plug 3 Control Circuit	P0673	P0673	P0673	P0673	--
Glow Plug 4 Control Circuit	P0674	P0674	P0674	P0674	--
Glow Plug 5 Control Circuit	P0675	P0675	P0675	P0675	--
Glow Plug 6 Control Circuit	P0676	P0676	P0676	P0676	--
Glow Plug 7 Control Circuit	P0677	P0677	P0677	P0677	--
Glow Plug 8 Control Circuit	P0678	P0678	P0678	P0678	--

Circuit/System Description

The glow plug controller has the ability to perform internal checks, an open or a short to ground on each of the glow plug circuits. If the glow plug controller senses a problem in a glow plug circuit, the glow plug on the affected cylinder will be disabled and the glow plug controller will send an error message to the engine control module (ECM). If this condition exists, the DTC will set.

Conditions for Running the DTC

Conditions for Setting the DTC

The glow plug controller detects that the glow plug control circuit is open, shorted to ground, or has more than 1 ohm of resistance.

Action Taken When the DTC Sets

DTCs P0671-P0678 are Type B DTCs.

Conditions for Clearing the DTC

DTCs P0671-P0678 are Type B DTCs.

Diagnostic Aids

If the battery is connected with the ignition ON, the glow plugs could be damaged without finding any circuit fault.

Reference Information

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

Circuit/System Verification

1. Verify that DTC P064C is not set.

⇒	If DTC P064C is set, refer to DTC P064C .

2. Ignition ON, engine OFF, observe the scan tool Glow Plug 1--Glow Plug 8 parameters. All Glow Plug parameters should closely match each other.
3. Refer to Testing for Intermittent Conditions and Poor Connections if you cannot duplicate the conditions.
4. Engine running, observe the DTC information with a scan tool. DTCs P0671-P0678 should not set.
5. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records data.

Circuit/System Testing

Important: If a glow plug is replaced and the tip is missing or burned off, the cylinder head must be removed and all debris be cleaned out of the cylinder.

1. Ignition ON, and the glow plugs not commanded ON, probe the affected glow plug with a test lamp connected to ground. Observe that the test lamp does not illuminate.

⇒	If the test lamp does illuminate, test the glow plug control circuit for a short to voltage or for a faulty glow plug control module (GPCM). Replace the affected glow plug after repair.

2. Ignition ON, probe the affected glow plug with a test lamp connected to ground. Command the glow plugs ON with a scan tool and observe the test lamp. The test lamp should illuminate.

⇒	If the test lamp does not illuminate, test the affected glow plug harness between the glow plug control module and the glow plug for an open, short to ground or high resistance.

3. Ignition OFF, and the affected glow plug disconnected, measure the resistance between the affected glow plug terminal A and ground with a DMM for less than 1 ohm.

⇒	If the resistance is more than 1 ohm, replace the affected glow plug.

4. Ignition OFF, and the glow plug control module harness disconnected, measure the resistance between the affected glow plug harness connector terminal A and the corresponding glow plug control module harness connector terminal for less than 1 ohm resistance.

⇒	If the resistance is more than 1 ohm, repair the harness.

⇒	If the resistance is less than 1 ohm, replace the glow plug control module.

Component Testing

With the igniting OFF and the affected glow plug disconnected, measure the resistance between the affected glow plug terminal of the glow plug and ground with a DMM for less than 1 ohm.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.