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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 P0120: Throttle Position Sensor Circuit >> Diagnostic Procedures

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. Turn ignition on, with engine off. With throttle closed, monitor TP sensor parameter on scan tool. If TP sensor value is greater than 25 percent, go to step  5. If TP sensor value is 25 percent or less, go to next step.
  3. Observe TP sensor with throttle closed. If TP sensor value is less than 6 percent, go to step  12. If TP sensor value is 6 percent or greater, go to next step.
  4. Using scan tool, clear DTC information and place vehicle into check mode. Operate vehicle within FREEZE FRAME conditions. If DTC resets, go to step  2. If DTC does not reset, see DIAGNOSTIC AIDS .
  5. Turn ignition off. Disconnect TP sensor harness connector. Turn ignition on, with engine off. Using scan tool, observe TP sensor parameter. If TP sensor value is greater than zero percent, go to step  7. If TP sensor value is zero percent, go to next step.
  6. Using test light connected to battery voltage, probe TP sensor harness connector terminal No. 2 (Brown wire). See Figure. If test light illuminates, go to step  8. If test light does not illuminate, go to step  10.
  7. Turn ignition off. Disconnect PCM harness connector. Check for short to voltage in Light Green wire between TP sensor harness connector terminal No. 3 and PCM harness connector C2 terminal No. 23 for 4-speed A/T or No. 11 for except 4-speed A/T. See Figure or Figure . Repair as necessary. After repairs, go to step  21. If circuit is okay, go to step  20.
  8. Using DVOM, check voltage at TP sensor harness connector terminal No. 1 (Yellow wire). If voltage reading is 5 volts, go to next step. If voltage reading is not 5 volts, go to step  11.
  9. Check for poor connections at PCM and TP sensor connectors. Repair as necessary. After repairs, go to step  21. If connections are okay, go to step  18.
  10. Turn ignition off. Disconnect PCM harness connector. Check for open in Brown wire between TP sensor harness connector terminal No. 2 and PCM harness connector C2 terminal No. 19 for 4-speed A/T or No. 9 for except 4-speed A/T. See Figure or Figure . Repair as necessary. After repairs, go to step  21. If circuit is okay, go to step  20.
  11. Turn ignition off. Disconnect PCM harness connector. Check for open or short in Yellow wire between TP sensor harness connector terminal No. 1 and PCM harness connector C2 terminal No. 2 for 4-speed A/T or No. 1 for except 4-speed A/T. See Figure or Figure . Repair as necessary. After repairs, go to step  21. If circuit is okay, go to step  20.
  12. Disconnect TP sensor harness connector. Using a fused jumper wire, jumper TP sensor harness connector terminals No. 1 (Yellow wire) and No. 3 (Light Green wire). See Figure. Using scan tool, monitor TP sensor parameter. If TP sensor value is greater than 90 percent, go to step  18. If TP sensor value is 90 percent or less, go to next step.
  13. Connect a test light between battery voltage and TP sensor harness connector terminal No. 3 (Light Green wire). Using scan tool, monitor TP sensor parameter. If TP sensor parameter is greater than 90 percent, go to next step. If TP sensor parameter is 90 percent or less, go to step  16.
  14. Turn ignition off. Disconnect PCM harness connector. Check for open or short in Yellow wire between TP sensor harness connector terminal No. 1 and PCM harness connector C2 terminal No. 2 for 4-speed A/T or No. 1 for except 4-speed A/T. See Figure or Figure . Repair as necessary. After repairs, go to step  21. If circuit is okay, go to next step.
  15. Check for poor connections at PCM and TP sensor connectors. Repair as necessary. After repairs, go to step  21. If connections are okay, go to step  20.
  16. Turn ignition off. Disconnect PCM harness connector. Check for open or short to ground in Light Green wire between TP sensor harness connector terminal No. 3 and PCM harness connector C2 terminal No. 23 for 4-speed A/T or No. 11 for except 4-speed A/T. See Figure or Figure . Repair as necessary. After repairs, go to step  21. If circuit is okay, go to next step.
  17. Check for poor connections at PCM. Repair as necessary. After repairs, go to step  21. If connections are okay, go to step  20.
  18. Check for poor connections at TP sensor connector. Repair as necessary. After repairs, go to step  21. If connections are okay, go to next step.
  19. Replace TP sensor. After repairs, go to step  21.
  20. Replace PCM. Perform PCM relearn procedure. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After replacing PCM, go to next step.
  21. 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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