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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 P0501 - Vehicle Speed Sensor Circuit >> 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. Install 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 a test light connected to ground, backprobe ignition feed circuit of VSS buffer/module connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 8).
  4. Using test light, backprobe between ignition feed circuit and ground circuit of VSS buffer/module connector. If test light illuminates, go to next step. If test light does not illuminate, go to step 9).
  5. Using DVOM on AC scale, backprobe both VSS input circuits of VSS buffer/module 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 11). If trans output speed (MPH) reading does not change, go to step 13).
  7. DTC is intermittent. If no additional DTCs are set, see DIAGNOSTIC AIDS. If any additional DTCs are set, go to applicable DTC test.
  8. Repair open in ignition feed circuit. After repairs, go to step 15).
  9. Repair open in ground circuit. After repairs, go to step 15).
  10. Check for open or short to ground in complete VSS input circuit. After repairs, go to step 15).
  11. Check for open or short to ground in VSS output circuit. Repair as necessary. After repairs, go to step 15). If circuit is okay, go to next step.
  12. Check for poor connections at VSS output terminal of buffer/module and PCM. Repair as necessary. After repairs, go to step 15). If connections are okay, go to step 14).
  13. Replace VSS buffer module. After replacing module, go to step 15).
  14. Replace PCM. After replacing PCM, go to next step.
  15. Using scan tool, select DTC, CLEAR INFO. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, 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, repeat step 2).
  16. Using scan tool, select CAPTURE INFO, REVIEW INFO. If any undiagnosed DTC(s) are displayed, go to applicable DTC test.
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