GM/Detroit 6.5L ENGINE CONTROLS – DTC P0380 Glow Plug Feedback Circuit

Refer to PCM, Glow Plugs, Underhood Fuse-Relay Center

Circuit Description
The glow plug system is used to assist in providing the heat required to begin combustion during cold engine temperatures. The glow plugs are heated before and during cranking, as well as initial engine operation. The PCM controls the glow plug ON times by monitoring coolant temperatures and glow plug voltage.

Conditions for Running the DTC
The ignition switch in the ON position.

Conditions for Setting the DTC
• The PCM has commanded glow plugs ON and the glow plug signal voltage is less than 4.0 volts.
or
• The PCM has commanded glow plugs OFF and the glow plug signal voltage is greater than 4.0 volts.
or
• When the PCM has commanded glow plugs ON and there is more than a 2 volt difference between glow plug voltage and ignition voltage.

Action Taken When the DTC Sets
• The PCM illuminates the malfunction indicator lamp (MIL) on the second consecutive drive trip that the diagnostic runs and fails.
• The PCM records the operating conditions at the time the diagnostic fails. The first time the diagnostic fails, the Failure Records will store this information. If the diagnostic reports a failure on the second consecutive drive trip, the Freeze Frame records the operating conditions at the time of failure and updates the Failure Records.

Conditions for Clearing the MiL/DTC
• The PCM will turn the MIL off after three consecutive trips without a fault condition.
• A History DTC clears after forty consecutive warm-up cycles, if this or any other emission related diagnostic does not report any failures
• The use of a scan tool.

Diagnostic Aids
If glow plug relay is stuck in the ON position, check for proper operation of glow plugs, refer to Glow Plug System Check. YJhen glow plugs are commanded ON by the Scan tool, an internal PCM timer protects the glow plugs from damage by cycling them ON for 3 seconds and the OFF for 12 seconds.
The glow plug output feed wire nut and battery feed wire nut at the relay should be checked for proper torque (5 N-m 44 lb in) and for corrosion.
An intermittent may be caused by the following:
• Poor connections.
• Rubbed through wire insulation.
• Broken wire inside the insulation.

Test Description
The number(s) below refer to the Step number(s) on the Diagnostic Table.
2. This step will determine if P0380 is a hard failure.
3. This step will determine if the PCM is requesting the glow plug system ON.
10. This step will determine if the glow plug relay has been activated and the output voltage has been seen by the PCM.

 

Leave a Reply

Your email address will not be published. Required fields are marked *