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: Cylinder #1 Glow Plug Control CircuitDTC 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
| • | The ignition is ON. |
| • | DTCs P0671-P0678 run continuously. |
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
| • | The control module illuminates the malfunction indicator lamp (MIL) on the second consecutive ignition cycle that the diagnostic runs and fails. |
| • | The control module records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the control module stores this information in the Failure Records. If the diagnostic reports a failure on the second consecutive ignition cycle, the control module records the operating conditions at the time of the failure. The control module writes the operating conditions to the Freeze Frame and updates the Failure Records. |
Conditions for Clearing the DTC
| • | The control module turns OFF the MIL after 3 consecutive ignition cycles that the diagnostic runs and does not fail. |
| • | A current DTC, Last Test Failed, clears when the diagnostic runs and passes. |
| • | A history DTC clears after 40 consecutive warm-up cycles, if no failures are reported by this or any other emission related diagnostic. |
| • | Clear the MIL and the DTC with a scan tool. |
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
Connector End View Reference
Electrical Information Reference
Scan Tool Reference
Circuit/System Verification
- Verify that DTC P064C is not set.
- If DTC P064C is set, refer to DTC P064C.
- Ignition ON, engine OFF, observe the scan tool Glow Plug 1-Glow Plug 8 parameters. All 8 Glow Plug parameters should closely match each other.
- Refer to Testing for Intermittent Conditions and Poor Connections if you cannot duplicate the conditions.
- Engine running, observe the DTC information with a scan tool. DTCs P0671-P0678 should not set.
- 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.
- Ignition ON, and the glow plugs not commanded ON, probe the affected glow plug with a test lamp connected to a ground. Observe that the test lamp does not illuminate.
- Ignition ON, probe the affected glow plug with an unpowered test lamp connected to ground. Command the glow plugs ON with a scan tool and observe the test lamp.
- Ignition OFF, and the affected glow plug disconnected, measure the resistance between the affected glow plug terminal and ground with a DMM for less than 1 ohm.
- Ignition OFF, and the glow plug control module harness disconnected, measure the resistance between the affected glow plug harness connector and the glow plug control module harness connector for less than 1 ohm resistance.
| ⇒ | 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. |
| ⇒ | 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. |
| ⇒ | If the resistance is greater than 1 ohm, replace all of the glow plugs. |
| ⇒ | If the resistance is greater than 1 ohm, repair the harness. |
| ⇒ | If the resistance is less than 1 ohm, replace the glow plug control module. |
Component Testing
With the ignition 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.
| ⇒ | If the resistance is greater than 1 ohm, replace the affected glow plug. Strongly suggest replacing all 8 due to possibility of damage that may result in customer return for related issue. |
Repair Instructions
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
| • | Control Module References for ECM replacement, setup, and programming |
