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Home >> GMC >> 2000 >> Envoy >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics - 4.3L >> Diagnostic Tests >> DTC P0121: Throttle Position Sensor Performance >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing OBD system check, go to next step.
  2. Install scan tool. Turn ignition on, with engine off. Using scan tool, observe TP sensor value. If TP sensor value is greater than 2 percent, go to step  6. If TP sensor value is not greater than 2 percent, go to next step.
  3. Slowly depress throttle to WOT while observing scan tool. TP sensor value should increase from zero percent to 100 percent. If operation is as specified, go to next step. If operation is not as specified, go to step  10.
  4. Release throttle. If TP sensor value is greater than 2 percent, go to step  6. If TP sensor value is not greater than 2 percent, go to next step.
  5. DTC is intermittent. If any additional DTCs are set, diagnose affected DTCs. If no additional DTCs are set, see DIAGNOSTIC AIDS .
  6. Disconnect TP sensor harness connector. If TP sensor value is zero volts, go to next step. If TP sensor value is not zero volts, go to step  9.
  7. Turn ignition off. Using a test light connected to battery voltage, probe ground circuit at TP sensor harness connector. If test light illuminates, go to next step. If test light does not illuminate, go to step  14.
  8. Turn ignition on. Using a test light connected to ground, probe 5-volt reference circuit at TP sensor harness connector. If test light illuminates, go to step  15. If test light does not illuminate, go to step  19.
  9. Turn ignition off. Disconnect VCM harness connector C2. Turn ignition on. Check voltage between ground and signal circuit at TP sensor harness connector. If voltage reading is greater than zero volts, go to step  13. If voltage reading is not greater than zero volts, go to step  22.
  10. Turn ignition off. Disconnect TP sensor harness connector. Using a fused jumper wire, jumper 5-volt reference circuit to signal circuit at TP sensor harness connector. Turn ignition on. If TP sensor value is 100 percent, go to step  17. If TP sensor value is not 100 percent, go to next step.
  11. Turn ignition on. Check voltage between ground and 5-volt reference circuit at TP sensor harness connector. If voltage reading is about 5.2 volts, go to next step. If voltage reading is not about 5.2 volts, go to step  16.
  12. Turn ignition off. Disconnect VCM harness connector C2. Check resistance in TP sensor signal circuit between TP sensor and VCM. If resistance is about zero ohms, go to step  22. If resistance is not about zero ohms, go to step  18.
  13. Repair short to voltage in TP sensor signal circuit. After repairs, go to step  24.
  14. Repair open in TP sensor ground circuit. After repairs, go to step  24.
  15. Repair short to voltage in 5-volt reference circuit. After repairs, go to step  24.
  16. Repair low voltage condition in 5-volt reference circuit. After repairs, go to step  24.
  17. Check for poor connection at TP sensor. If connection is faulty, go to next step. If connection is okay, go to step  19.
  18. Repair circuit as necessary. After repairs, go to step  24.
  19. Check for binding or sticking throttle linkage and/or cables. If a problem is found, go to next step. If no problem is found, go to step  21.
  20. Repair throttle linkage as necessary. After repairs, go to step  24.
  21. Replace TP sensor. After replacing sensor, go to step  24.
  22. Check for poor connection as VCM. Repair as necessary. After repairs, go to step  24. If connection is okay, go to next step.
  23. Replace VCM. Program replacement VCM using required equipment. After replacing VCM, go to next step.
  24. Using scan tool, clear DTCs. Start and warm engine to normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function then enter DTC P0121. If scan tool indicates this test ran and passed, go to next step. If scan tool does not indicate this test ran and passed, go to step  2.
  25. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTCs are displayed, diagnose affected DTCs. If no undiagnosed DTCs are displayed, system is okay.
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