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Home >> Isuzu >> 1996 >> Hombre S >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Testing >> DTC P0502 - VSS Circuit Low Input >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
    CAUTION: Support lower control arms so drive axles are in normal horizontal position or drive axles will be damaged.
  2. Raise and support drive axles. Start engine. With engine at idle, place transmission in Drive. Using scan tool, monitor vehicle speed. If displayed vehicle speed is greater than zero MPH, go to next step. If displayed vehicle speed is zero MPH, go to step 4).
  3. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. Using scan tool, monitor vehicle speed. If displayed vehicle speed is greater than zero MPH, go to step 12). If displayed vehicle speed is zero MPH, go to next step.
  4. Turn ignition off. Disconnect PCM connector. Connect DVOM between VSS high and VSS low terminal, rotate drive wheels and measure AC voltage. If voltage is greater than, or equal to .5 volt, go to next step. If voltage is less than .5 volt, go to step 7).
  5. Check vehicle for most current PCM calibration ID number. If ID number is found, go to step 13). If ID number is not found, go to next step.
  6. Update PCM with latest calibration ID and go to step 14).
  7. Measure resistance between VSS high and VSS low terminals. If resistance is greater than 1950 ohms, go to next step. If resistance is equal to or less then 1950 ohms, go to step 9).
  8. Check for an open or short to ground in VSS high circuit. Repair as necessary. After repair is completed, go to step 14). If circuit is okay, go to step 11).
  9. If resistance value is 1300-1950 ohms, go to next step. If was not as specified, go to step 11).
  10. Check for an open or short to ground in VSS high circuit. Repair as necessary. After repair is completed, go to step 14). If circuit is okay, go to next step.
  11. Remove VSS and measure resistance between VSS high and VSS low terminals. If resistance is 1300-1950 ohms, go to step 13). If resistance is not as specified, go to next step.
  12. Replace VSS. After repair is completed, go to step 14).
  13. Replace PCM. Program replacement PCM using required equipment. After repair is completed, go to next step.
  14. Using scan tool, select CLEAR INFO or CLEAR DTCS function to clear DTCs. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function then enter DTC P0502. If scan tool indicates TEST RAN AND PASSED, go to next step. If scan tool does not indicate TEST RAN AND PASSED, repeat step 2).
  15. If any other DTCs are set, diagnose DTCs as necessary. If no other DTCs are set, no problem is indicated at this time.
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