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Home >> GMC >> 1997 >> Forward Control 4.3 W, L35, Automatic >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 10 (Engine Controls - Tests W/Codes - 6.5L Diesel (P Series)) >> Diagnostic Trouble Codes >> DTC P0380 - Glow Plug Circuit Performance >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different variant/trim than selected.
  1. Perform Powertrain ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the BASIC TESTING article. Then go to next step.
  2. Turn ignition on, with engine off. Using a test light connected to ground, probe battery side of glow plug relay. If test light illuminates, go to next step. If test light does not illuminate, go to step 9).
  3. Using scan tool, command glow plugs on. Observe GLOW PLUG SYSTEM display on scan tool. If scan tool displays glow plug value at 10-14 volts, go to next step. If scan tool does not display glow plug value at 10-14 volts, go to step 5).
  4. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
  5. Turn ignition off. Disconnect glow plug relay connector. Turn ignition on, with engine off. Using test light connected to ground, probe ignition feed circuit of glow plug relay connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 10).
  6. Turn ignition on, with engine off. Connect test light between ignition feed circuit and ground circuit of glow plug relay connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 11).
  7. Turn ignition on, with engine off. Leave glow plug relay connector disconnected. Using DVOM, probe control circuit of glow plug relay connector to ground. Using scan tool, command glow plugs on. If battery voltage is present, go to next step. If battery voltage is not present, go to step 12).
  8. Reconnect glow plug relay connector. Turn ignition on, with engine off. Using test light connected to ground, probe glow plug side of glow plug relay connector. Using scan tool, command glow plugs on. If test light illuminates when glow plugs are commanded on, go to step 14). If test light does not illuminate when glow plugs are commanded on, go to step 16).
  9. Check for poor connections at glow plug relay control terminal of PCM. Repair terminal as necessary. After repairs, go to step 18).
  10. Repair open or short to ground in ignition feed circuit. After repairs, go to step 18).
  11. Repair open or poor connections in ground circuit. After repairs, go to step 18).
  12. Check for open or short to ground in control circuit. Repair as necessary. After repairs, go to step 18). If circuit is okay, go to next step.
  13. Check for poor connections at glow plug relay control terminal of PCM. Repair terminal as necessary. After repairs, go to step 18). If terminals are okay, go to step 17).
  14. Check for open or short to ground in signal circuit. Repair as necessary. After repairs, go to step 18). If circuit is okay, go to next step.
  15. Check for poor connections at glow plug relay signal terminal of PCM. Repair terminal as necessary. After repairs, go to step 18). If terminals are okay, go to step 17).
  16. Replace glow plug relay. After replacing relay, go to step 18).
  17. Replace PCM. After replacing PCM, go to next step.
  18. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P0380. Operate vehicle within the conditions for setting this DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
  19. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.
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