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HOMESERVICE MANUALSGMC1999FORWARD CONTROL 5.7 R, AUTOMATICREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT CARSECTION 77 (ENGINE CONTROLS SELF-DIAGNOSTICS - 6.5L)DIAGNOSTIC TESTSDTC P0380: GLOW PLUG CIRCUIT PERFORMANCE (CA)DIAGNOSTIC PROCEDURES
1999 GMC Forward Control 5.7 R, Automatic

Diagnostic Procedures

1999 GMC Forward Control 5.7 R, AutomaticSECTION Diagnostic Procedures
WARNING: This page does not describe the selected car, but rather 6 other vehicles, including the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, 2002 Chevrolet RV Cutaway, and 2002 Chevrolet Cutaway. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check-Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. If this DTC set after an PCM reflash, connect a scan tool. Turn ON the ignition, with the engine OFF. Observe the Glow Plug System Type parameter on the scan tool. Does the scan tool display the Glow Plug System Type as California? If yes, go to next step. If no, see GLOW PLUG SYSTEM RELEARN PROCEDURE  under PROGRAMMING.
  3. Connect a scan tool. Turn ON the ignition, with the engine OFF. Use the scan tool in order to command the glow plugs ON and OFF. Observe the glow plug feedback parameter on the scan tool. Does the scan tool display the glow plug feedback parameter as 5.0-6.0 V? If yes, go to step  7 . If no, go to next step.
  4. Does the scan tool display a glow plug voltage more than 6.0 V? If yes, go to step  20 . If no, go to next step.
  5. Does the scan tool display a glow plug voltage more than 0.45 V? If yes, go to step  10 . If no, go to next step.
  6. Turn ON the ignition, with the engine OFF. Touch the battery feed stud on the glow plug relay with an unpowered test lamp connected to ground. Does the test lamp illuminate? If yes, go to step  8 . If no, go to step  23 .
  7. The DTC is intermittent. If no additional DTCs are stored, see DIAGNOSTIC AIDS  . If any additional DTCs were stored, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  .
  8. Disconnect the glow plug relay middle connector. Turn ON the ignition, with the engine OFF. With an unpowered test lamp connected to ground, probe the glow plug relay harness ignition feed circuit. Does the test lamp illuminate? If yes, go to next step. If no, go to step  15 .
  9. Turn ON the ignition, with the engine OFF. Connect an unpowered test lamp to battery voltage, probe the glow plug relay harness ground circuit. Does the test lamp illuminate? If yes, go to next step. If no, go to step  16 .
  10. Turn ON the ignition, with the engine OFF. Verify that the glow plug relay harness is disconnected. With an unpowered test lamp connected to ground, probe the glow plug relay control circuit at the glow plug relay harness connector. Use a scan tool in order to command the glow plugs ON and OFF. Does the test lamp illuminate with the scan tool command ON? If yes, go to step  12 . If no, go to next step.
  11. Does the test lamp illuminate all of the time? If yes, go to step  22 . If no, go to step  17 .
  12. Verify that the glow plug relay is still disconnected. Turn ON the ignition, with the engine OFF. Using the Connector Test Adapter Kit (J 35616-A), jumper the glow plug control circuit to the glow plug signal circuit scan tool. Use a scan tool in order to command the glow plugs ON. Observe the scan tool while the glow plugs are commanded ON. Does the glow plug parameter voltage measure near Battery Voltage? If yes, go to next step. If no, go to step  19 .
  13. Turn OFF the ignition. Disconnect the right and left bank glow plug output circuit connectors at the glow plug relay. With an unpowered test lamp connected to battery voltage, probe each circuit. Does the test lamp illuminate for each circuit? If yes, go to step  25 . If no, go to next step.
  14. Turn OFF the ignition. Disconnect each glow plug connector at the glow plug that did not illuminate the test lamp. With an unpowered test lamp connected to battery voltage, probe the terminal on the glow plug. Does each glow plug illuminate the test lamp? If yes, go to step  25 . If no, go to step  24 .
  15. Repair the open or short to ground in the glow plug relay ignition 1 voltage circuit. After repairs, go to step  28 .
  16. Repair the open circuit or poor connections in the glow plug relay harness ground circuit. After repairs, go to step  28 .
  17. Inspect the glow plug relay control circuit for an open or short to ground and repair as necessary. Did you find and correct the condition? If yes, go to step  28 . If no, go to next step.
  18. Inspect the glow plug relay control circuit for a proper connection at the PCM and replace the terminal if necessary. Did you find and correct the condition? If yes, go to step  28 . If no, go to step  27 .
  19. Inspect the glow plug relay signal circuit for an open or short to ground and repair as necessary. Did you find and correct the condition? If yes, go to step  28 . If no, go to step  26 .
  20. Inspect the glow plug relay signal circuit for a proper connection at the PCM and replace the terminal if necessary. Did you find an improper connection and make the necessary replacement? If yes, go to step  28 . If no, go to next step.
  21. Inspect for a short to voltage in the glow plug relay signal circuit and repair as necessary. Did you find the improper condition? If yes, go to step  28 . If no, go to step  25 .
  22. Inspect for a short to voltage in the glow plug control circuit and repair as necessary. Did you find the improper condition? If yes, go to step  28 . If no, go to step  27 .
  23. Repair the open or poor connection on the battery voltage circuit. After repairs, go to step  28 .
  24. Replace any glow plug that did not illuminate the test lamp. After repairs, go to step  28 .
  25. Inspect for an open or poor connection in the glow plug harness. Did you find and correction the condition? If yes, go to step  28 . If no, go to next step.
  26. Replace the glow plug relay. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. After repairs, go to step  28 .
  27. Replace the PCM. See appropriate REMOVAL, OVERHAUL & INSTALLATION article. Reprogram PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  28. Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step  2 .
  29. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no, system is okay.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.