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Home >> GMC >> 1997 >> Forward Control 4.3 W, L35, Automatic >> Repair and Diagnosis >> External Pages >> Different variant/trim >> Section 11 (Engine Controls - Tests W/Codes - 7.4L (P Series)) >> Diagnostic Trouble Codes >> DTC P1406 - EGR Valve Pintle Position Circuit >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different variant/trim than selected.
  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the F - BASIC TESTING - 7.4L article. After performing OBD system check, go to next step.
  2. Install scan tool. Turn ignition on, with engine off. Using scan tool, monitor EGR pintle position. If scan tool indicates zero percent, go to next step. If scan tool does not indicate zero percent, go to step 8).
  3. Start engine. Using scan tool, select MISCELLANEOUS TESTS, EGR CONTROL and cycle EGR valve through 25, 50, 75 and 100 percent positions while observing DESIRED EGR POSITION and ACTUAL EGR POSITION. If positions are close to commanded positions, see DIAGNOSTIC AIDS. If positions are not close to commanded positions, go to next step.
  4. Turn ignition off. Disconnect EGR valve connector. Turn ignition on, with engine off. Connect test light between control circuit and ignition feed circuit of EGR valve connector. Using scan tool, command EGR position to 100 percent. If test light illuminates, go to step 26). If test light does not illuminate, go to next step.
  5. Using test light, probe ignition feed circuit of EGR valve connector to ground. If test light illuminates, go to next step. If test light does not illuminate, go to step 12).
  6. Check for poor connections at VCM and EGR valve. Also, check for open in ground circuit. If a problem is found, go to next step. If a problem is not found, go to step 8).
  7. Repair VCM and EGR valve connections or open in ground circuit. After repairs, go to step 40).
  8. Turn ignition off. Install scan tool. Disconnect EGR valve connector. Turn ignition on, with engine off. Using scan tool, monitor EGR pintle position. If scan tool indicates zero percent, go to step 16). If scan tool does not indicate zero percent, go to next step.
  9. Check if DTC P0108 is also set. If DTC P0108 is set, go to DTC P0108 . If DTC P0108 is not set, go to next step.
  10. Check for short to voltage in pintle position circuit. If a problem was found, go to next step. If a problem was not found, go to step 12).
  11. Repair short to voltage in pintle position circuit. Go to step 40).
  12. Check if 20-amp ENG-1 fuse is blown. If fuse is blown, go to step 13). If fuse is not blown, go to step 15).
  13. Replace 20-amp ENG-1 fuse. After replacing fuse, go to next step.
  14. Repair short to ground in ignition feed circuit. After repairs, go to step 40).
  15. Repair open in ignition feed circuit. After repairs, go to step 40).
  16. Using test light, probe ground circuit of EGR valve connector to battery voltage. If test light illuminates, go to step 19). If test light does not illuminate, go to next step.
  17. Check for open in ground circuit. If a problem was found, go to next step. If a problem was not found, go to step 19).
  18. Repair open in ground circuit. After repairs, go to step 40).
  19. Using test light, probe control circuit of EGR valve connector to battery voltage. If test light illuminates, go to next step. If test light does not illuminate, go to step 23).
  20. Unplug VCM. With test light connected to battery voltage, probe EGR valve harness connector control circuit terminal. If test light is on, go to next step. If not, go to step 39).
  21. Check for short to ground in control circuit. If a problem was found, go to next step. If a problem was not found, go to step 23).
  22. Repair short to ground in control circuit. After repairs, go to step 40).
  23. Check for poor connection at EGR valve. If a problem was found, go to next step. If a problem was not found, go to step 25).
  24. Repair EGR valve connection. After repairs, go to step 40).
  25. Replace EGR valve. After replacing EGR valve, go to step 40).
  26. Using DVOM, check voltage between ground circuit and 5-volt reference circuit of EGR valve connector. If voltage is about 5 volts, go to step 31). If voltage is not about 5 volts, go to next step.
  27. Using DVOM, check voltage between 5-volt reference circuit of VCM connector and ground. If voltage is about 5 volts, go to next step. If voltage is not about 5 volts, go to step 29).
  28. Check for poor connection at VCM. If a problem was found, go to next step. If a problem was not found, go to step 30).
  29. Repair VCM connection. After repairs, go to step 40).
  30. Repair open in 5-volt reference circuit. After repairs, go to step 40).
  31. Using test light, probe pintle position circuit of EGR valve connector to battery voltage. If test light illuminates, go to step 34). If test light does not illuminate, go to next step.
  32. Check for short to ground in pintle position circuit. If a problem was found, go to next step. If a problem was not found, go to step 34).
  33. Repair short to ground in pintle position circuit. After repairs, go to step 40).
  34. Using Connector Test Kit (J 35616-A), install adapters in all circuits between engine harness connector and EGR valve connector. Connect DVOM between pintle position circuit of EGR valve connector and ground. Using scan tool, command EGR position to 100 percent. Observe voltage when EGR is commanded on. If voltage is 3.5-5 volts, go to next step. If voltage is not 3.5-5 volts, go to step 36).
  35. Check for open in pintle position circuit. Also, check for poor connection at EGR valve. If a problem was found, go to step 37). If a problem was not found, go to next step.
  36. Check for poor connection at VCM. If a problem was found, go to step 37). If a problem was not found, go to step 39).
  37. Repair open in pintle position circuit. After repairs, go to step 40).
  38. Repair VCM connection. After repairs, go to step 40).
  39. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to step 41).
  40. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter DTC P1406. 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).
  41. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTCs are displayed, go to applicable DTC test.
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