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Home >> GMC >> 1999 >> Forward Control 6.5 F, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - Tests W/Codes - DTC P0100-P0134 >> DTC P0121 >> DTC P0121: TP Sensor Performance (2.4L "N" Body) >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK under SELF-DIAGNOSTIC SYSTEM in SELF-DIAGNOSTICS INTRODUCTION article. After performing OBD system check, go to next step.
  2. Turn ignition on, with engine off. Using scan tool, check for DTCs. If any EGR, A/C or fuel tank pressure sensor DTCs are present, diagnose affected DTC. If specified DTCs are not present, go to next step.
  3. If scan tool displays a TP voltage at less than.9 volt when throttle is fully closed, go to next step. If TP voltage is not less than.9 volt when throttle is fully closed, go to step  6.
  4. Observing scan tool, depress accelerator to floor, and then slowly release pedal. TP sensor angle value should increase steadily to about 98 percent when pedal is depressed and decrease steadily to about one percent when pedal is released. If TP sensor angle value is as specified, go to next step. If TP sensor angle value is not as specified, go to step  6.
  5. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME as possible. If TP sensor angle value-versus-RPM value is greater than specified value in conditions for setting DTC, go to next step. If TP sensor angle value-versus-RPM value is not greater than the specified value in conditions for setting DTC, go to step  16.
  6. Turn ignition off. Disconnect TP sensor connector. Turn ignition on. Observe TP sensor display on scan tool. If TP sensor voltage is near zero volts, go to next step. If TP sensor voltage is not as specified, go to step  8.
  7. Using a fused jumper wire, jumper 5-volt reference circuit and signal circuit together at TP sensor harness connector. If TP sensor voltage is about 5 volts, go to step  9. If TP sensor voltage is not as specified, go to step  10.
  8. Check TP sensor signal circuit for short to voltage. Repair as necessary. After repairs, go to step  16. If circuit is okay, go to step  15.
  9. Using a test light connected to battery positive, probe TP sensor ground circuit at TP sensor harness connector. If test light illuminates, go to step  11. If test light does not illuminate, go to step  12.
  10. Check TP sensor 5-volt reference circuit and signal circuit for poor connections or terminal tension. Repair as necessary. After repairs, go to step  16. If no problem is found, go to step  13.
  11. Check TP sensor harness connector for poor connections or terminal tension. Repair as necessary. After repairs, go to step  16. If no problem is found, go to step  14.
  12. Check TP sensor ground circuit for poor connections or terminal tension at PCM. Repair as necessary. After repairs, go to step  16. If no problem is found, go to step  15.
  13. Check PCM harness connectors for poor connections or terminal tension. Repair as necessary. After repairs, go to step  16. If no problem is found, go to step  15.
  14. Turn ignition off. Replace TP sensor. After repairs, go to step  16.
  15. Replace PCM. After repairs, go to next step.
  16. 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.
  17. 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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