Glow Plug System: Testing and Inspection

GLOW PLUG SYSTEM DIAGNOSIS

CIRCUIT DESCRIPTION
The glow plug system is used to assist in providing the heat required to begin combustion during engine starting at cold ambient temperatures. The glow plugs are heated before and during cranking, as well as during the engine operation. The engine control module (ECM) controls the glow plug ON times by monitoring coolant temperatures and glow plug voltage. This system check will check the glow plugs and the glow plug feed circuit coming from the relay/controller.

DIAGNOSTIC AIDS
If the glow plug relay or controller is stuck in the ON position, check for proper operation of the glow plugs. When the glow plugs are commanded ON by the scan tool, an internal engine control module (ECM) timer protects the glow plugs from damage by cycling them ON for 3 seconds and then OFF for 12 seconds. Most glow plug system failures are covered by DTC P0380. If no DTCs are stored, the vehicle is hard to start and white smoke is present during cranking or after the vehicle is started, the most likely cause of failure is the glow plugs.

TEST DESCRIPTION

Steps 1-2:

Steps 3-8:

Steps 9-11:

The numbers below refer to the step numbers on the diagnostic table.
2. This step will make sure there are no other DTCs stored that will affect the operation of the glow plug system.
3. This step will check each glow plug for an open.
4. This step will check each glow plug feed circuit for an open.