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Home >> GMC >> 2000 >> C3500 HD 6.5 F, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - Diesel >> Diagnostic Tests >> DTC P0501: Vehicle Speed Sensor Circuit >> Diagnostic Procedures

Diagnostic Procedures

  1. If OBD system check has been performed, go to next step. If OBD system check has not been performed, see ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM.
  2. Connect scan tool. Raise drive wheels. With engine running, place transmission in any drive range. With drive wheels rotating, if vehicle speed increases when drive wheel speed increases, go to step  7. If vehicle speed does not increase when drive wheel speed increases, go to next step.
  3. Place transmission in Park. Using test light connected to ground, backprobe ignition feed circuit at VSS buffer/module harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step  8.
  4. Backprobe test light between ground circuit and ignition feed circuit at VSS buffer/module harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step  9.
  5. Using DVOM set to AC scale, backprobe both VSS input circuits at VSS buffer/module harness connector to each other. Place transmission in any drive range with drive wheels rotating. If voltage increases as drive wheel speed increases, go to next step. If voltage does not increase as drive wheel speed increases, go to step  10.
  6. If scan tool displays a trans output speed (MPH) increase with drive wheel speed increase, go to step  13. If trans output speed (MPH) reading does not change, go to step  12.
  7. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS . If any additional DTCs are set, perform appropriate DTC test.
  8. Repair open in VSS ignition feed circuit. After repairs, go to step  18.
  9. Repair open in VSS ground circuit. After repairs, go to step  18.
  10. Check for open or short to ground in VSS input circuit. After repairs, go to step  18. If circuit is okay, go to next step.
  11. Check for poor connection at VSS. Repair as necessary. After repairs, go to step  18. If connection is okay, go to step  15.
  12. Using DVOM connected to ground, backprobe VSS output circuit at VSS buffer/module harness connector. Place transmission in any drive range with drive wheels rotating. If voltage is present, go to next step. If voltage is not present, go to step  16.
  13. Check for open or short to ground in VSS output circuit. Repair as necessary. After repairs, go to step  18. If circuit is okay, go to next step.
  14. Check VSS output circuit for poor connection at PCM. Repair as necessary. After repairs, go to step  18. If connection is okay, go to step  17.
  15. Replace VSS sensor. After repairs, go to step  18.
  16. Replace VSS buffer/module. See VEHICLE SPEED BUFFER  After repairs, go to step  18.
  17. Replace PCM. Perform PCM relearn procedures. See PROGRAMMING . After repairs, go to next step.
  18. Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, and then enter DTC P0501. 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, go to step  2.
  19. Using scan tool, check for DTCs. If any undiagnosed DTCs are set, perform appropriate DTC test. If no DTCs are set, system is okay.
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