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Home >> Chevrolet >> 2000 >> Venture Plus >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics >> 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. Turn ignition on, with engine off. Using scan tool, observe TP angle reading while slowly opening throttle. TP angle should increase steadily and evenly from closed throttle value (zero percent) to wide open throttle value (100 percent). If TP angle reading is as specified, see DIAGNOSTIC AIDS . If TP angle reading is not as specified, go to next step.
  3. Turn ignition off. Disconnect TP sensor harness connector. Turn ignition on, with engine off. Using scan tool, observe the TP voltage parameter. If TP voltage parameter is about zero volts, go to next step. If TP voltage parameter is not about zero volts, go to step  5.
  4. Turn ignition off. Connect a fused jumper wire between the TP sensor harness connector 5-volt reference circuit and signal circuit. Turn ignition on, with engine off. Using scan tool, observe TP sensor voltage parameter. If TP sensor voltage parameter is 5 volts, go to step  8. If TP sensor voltage parameter is not 5 volts, go to step  6.
  5. Check TP sensor signal circuit for short to voltage. Repair as necessary. After repairs, go to step  12. If circuit is okay, go to step  11.
  6. Check TP sensor 5-volt reference circuit for high resistance or a poor connection at PCM. Repair as necessary. After repairs, go to step  12. If circuit is okay, go to next step.
  7. Check TP sensor signal circuit for high resistance, or a poor connection at PCM. Repair as necessary. After repairs, go to step  12. If circuit is okay, go to step  11.
  8. Check TP sensor ground circuit for high resistance or a poor connection at PCM. Repair as necessary. After repairs, go to step  12. If circuit is okay, go to next step.
  9. Check for poor connections at TP sensor harness connector. Repair as necessary. After repairs, go to step  12. If connections are okay, go to next step.
  10. Replace TP sensor. After replacing sensor, go to step  12.
  11. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, go to next step.
  12. Using scan tool, clear DTCs. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle as close to conditions recorded in FREEZE FRAME as possible. Monitor SPECIFIC DTC info for this DTC. If scan tool indicates that this DTC failed this ignition, go to step  2. If scan tool does not indicate that this DTC failed this ignition, system is okay.
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