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Home >> Chevrolet >> 2001 >> Prizm Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics - 1.8L >> Diagnostic Tests >> DTC P0121: Throttle Position Sensor System Performance >> Diagnostic Procedures
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Diagnostic Procedures

  1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check, go to next step.
  2. Using scan tool, monitor TP sensor angle parameter. Monitor scan tool while depressing accelerator pedal several times. If TP sensor parameter varies steadily between 10 percent (released position) and 80 percent (depressed position), go to next step. If TP sensor parameter is not as specified, or reading is erratic, go to step  4.
  3. Using scan tool, clear DTC information and place vehicle into check mode. Operate vehicle within FREEZE FRAME conditions. If DTC resets, go to next step. If DTC does not reset, see DIAGNOSTIC AIDS .
  4. Disconnect TP sensor harness connector. Using scan tool, monitor TP sensor angle. If TP sensor angle is greater than zero percent, go to step  6. If TP sensor angle is zero percent, go to next step.
  5. Connect a test light between TP sensor harness connector terminals No. 1 (Yellow wire) and No. 3 (Light Green wire). See Figure. Using scan tool, monitor TP sensor angle. If TP sensor value is greater than 90 percent, go to step  8. If TP sensor value is 90 percent or less, go to step  7.
  6. Turn ignition off. Check for short to battery voltage in Light green wire between TP sensor and PCM. Check for open in Brown wire between TP sensor and PCM. Check TP sensor harness connector for proper connection. Repair as necessary. After repairs, go to step  10. If circuits and connection are okay, go to step  9.
  7. Turn ignition off. Check for an open or short in Light Green wire between TP sensor and PCM. Check for high resistance in Yellow wire between TP sensor and PCM. Repair as necessary. After repairs, go to step  10. If circuits are okay, go to step  9.
  8. Replace TP sensor. After replacing sensor, go to step  10.
  9. Replace PCM. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After replacing PCM, go to next step.
  10. Turn ignition on, with engine off. Using scan tool, clear DTC information. Road test vehicle within conditions for running DTC. See CODE ENABLE CRITERIA . Check for DTCs. If no DTCs are stored, repair is complete. If any DTCs are stored, diagnose affected DTCs.
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