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Home >> Chevrolet >> 2002 >> Impala LS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System Self-Diagnostics - 3.8L >> Diagnostic Tests >> DTC P0121: TP Sensor Performance >> Diagnostic Procedures
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Diagnostic Procedures

NOTE: If any other DTCs are set, diagnose those DTCs first.
  1. Perform Diagnostic System Check - Engine Controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing Diagnostic System Check - Engine Controls, go to next step.
  2. Turn ignition on, engine off. Using scan tool, observe TP sensor angle parameter while slowly opening throttle to WOT. Parameter should be at zero percent at closed throttle and 98 percent at WOT. Does TP angle increase steadily and evenly from closed throttle value to more than wide open throttle value? If yes, go to next step. If no, go to step  4.
  3. Observe FREEZE FRAME/FAILURE RECORDS for this DTC. Turn ignition off for 30 seconds. Operate vehicle within Conditions for Running DTC or as close to FREEZE FRAME/FAILURE RECORDS as possible. Does DTC fail this ignition cycle? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  4. Turn ignition off. Disconnect TP sensor connector. Turn ignition on, engine off. Using scan tool, observe TP sensor voltage parameter. Does scan tool indicate TP sensor voltage is zero? If yes, go to next step. If no, go to step  6.
  5. Turn ignition off. Connect a fused jumper wire between the 5-volt reference circuit and the signal circuit at the TP sensor harness connector. Turn on the ignition, with the engine off. Observe the TP sensor voltage parameter with a scan tool. Does the scan tool indicate TP sensor voltage at 5 volts? If yes, go to step  9. If no, go to step  7.
  6. Test the TP sensor signal circuit for a short to voltage with the DMM. Did you find and correct the condition? If yes, go to step  15. If no, go to step  12.
  7. Test the TP sensor 5-volt reference circuit for an open or for high resistance with the DMM. Did you find and correct the condition? If yes, go to step  15. If no, go to next step.
  8. Test the TP sensor signal circuit for an open or for high resistance. Did you find and correct the condition? If yes, go to step  15. If no, go to step  11.
  9. Test the TP sensor low reference circuit for an open or for high resistance. Did you find and correct the condition? If yes, go to step  15. If no, go to next step.
  10. Test the TP sensor 5-volt reference circuit for high resistance. Did you find and correct the condition? If yes, go to step  15. If no, go to next step.
  11. Inspect for a poor connection at the TP sensor harness connector. Did you find and correct the condition? If yes, go to step  15. If no, go to step  13.
  12. Inspect for a poor connection at the Powertrain Control Module (PCM) harness connector. Did you find and correct the condition? If yes, go to step  15. If no, go to step  14.
  13. Replace TP sensor. After repairs, go to step  15.
  14. Replace PCM. Program replacement PCM. See POWERTRAIN CONTROL MODULE  under PROGRAMMING. After repairs, go to next step.
  15. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate vehicle within Conditions for Running DTC. Does DTC run and pass? If yes, go to next step. If no, go to step  2.
  16. Using scan tool, observe stored information. Does scan tool displays any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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