GM Service Manual Online
For 1990-2009 cars only
Makes 🢒 GMC_Truck 🢒 1998 🢒 GMC P42 Commercial Chassis 🢒 Engine 🢒 Engine Controls - 6.5L (L65) 🢒 Glow Plug System Check

Refer to

Engine Controls (Cell 22: Ignition Controls)


Object Number: 191295 Size: FS
Engine Controls Components
Engine Controls (Cell 22: Fuel Controls 1)
Engine Controls (Cell 22: Power and Grounds)
ESD Notice
ESD Notice
 .

Circuit Description

The glow plug system is used in order 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 initial engine operation. The PCM controls the amount of time the glow plugs are energized by monitoring the coolant temperatures and the glow plug voltage. This system check will check the glow plugs and the glow plug feed circuit coming from the relay.

Diagnostic Aids

If the glow plug relay is stuck in the ON position, check for proper operation of glow plugs. When the 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 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 vehicle is started. The most likely cause of failure is the glow plugs.

Test Description

The numbers below refer to the numbers on the diagnostic table.

  1. This step will ensure that the OBD system check is performed.

    2.

  2. This step will ensure that there are no other DTCs stored that will affect the operation of the glow plug system.

    3.

  3. This step will check each glow plug for an open.

    4.

  4. This step will check each glow plug feed circuit for an open.

Step

Action

Value(s)

Yes

No

1

Important: Before clearing the DTCs, use the Scan Tool Capture Info in order to record the Freeze Frame and the failure records for reference, as the data will be lost when the Clear Info function is used.

Was the Powertrain On-Board Diagnostic (OBD) System Check performed?

--

Go to Step 2

Go to A Powertrain On Board Diagnostic (OBD) System Check

2

Is DTC:

    • P0117
    • P0118
    • P0380

stored as history or current codes?

--

Go to the applicable DTC table

Go to Step 3

3

  1. Turn the ignition OFF.
  2. Disconnect all of the glow plugs.
  3. With a test light connected to B+, probe the spade terminal on each glow plug.

Do all of the glow plugs turn the test light ON?

--

Go to Step 4

Go to Step 9

4

  1. Turn the ignition ON with the engine OFF.
  2. The glow plugs are still disconnected.
  3. Use a test light in order to jumper each glow plug connector terminal to ground.
  4. Use a Scan Tool in order to command the glow plugs ON.

Does each circuit turn the test light ON?

--

Go to Step 5

Go to Step 10

5

Does the test light stay ON all the time for each glow plug terminal (even when the glow plugs aren't commanded ON)?

--

Go to Step 6

Go to Step 11

6
  1. Disconnect the glow plug output (gray) cable from the glow plug relay.
  2. Probe each glow plug terminal with a test light connected to ground.

Is the test light ON for all terminals?

--

Go to Step 7

Go to Step 8

7

Repair the short to voltage on the glow plug output circuit or the short to voltage on the glow plug signal circuit.

Is the action complete?

--

Go to Step 11

--

8

Replace the glow plug relay. Refer to Glow Plug Relay Replacement .

Is the action complete?

--

Go to Step 11

--

9

Replace all of the glow plugs that do not turn the test light ON. Refer to Glow Plug Replacement - Left Side or Glow Plug Replacement - Right Side .

Is the action complete?

--

Go to Step 11

--

10

Repair the open in each circuit that does not turn the test light ON.

Is the action complete?

--

Go to Step 11

--

11

Operate the vehicle within the conditions under which system was noted.

Does the system operate properly?

--

The System is OK

Go to Step 1