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Home >> Buick >> 1996 >> Century Custom >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - Tests W/Codes - 3.1L >> Diagnostic Trouble Codes >> DTC P0121 - TP Sensor System Performance >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) System Check. CHECK. After performing OBD system check, go to next step.
  2. Turn ignition on, with engine off. Using scan tool, select ENG 1 data list. Monitor MAP sensor reading. If MAP sensor value is less than 55 kPa, go to next step. If MAP sensor scan tool value is 55 kPa or more, go to step 6).
  3. Disconnect MAP sensor connector. Connect a test light between 5-volt reference circuit and signal circuit terminals at MAP sensor harness connector. If MAP sensor value is less than 55 kPa, go to step 5). If MAP sensor value is 55 kPa or more, go to next step.
  4. Check for an open or short to ground in MAP sensor signal circuit. Repair as necessary. After repair is completed, go to step 13). If circuit is okay, go to step 12).
  5. Replace MAP sensor. After repair is completed, go to step 13).
  6. Observing scan tool, depress accelerator to floor, then slowly release pedal. TP sensor angle value should increase steadily to 100 percent when pedal is depressed and decrease steadily to zero percent when pedal is released. If TP sensor angle value is as specified, see DIAGNOSTIC AIDS. If TP sensor angle value is not as specified, go to next step.
  7. Disconnect TP sensor connector. Observe TP sensor display on scan tool. If TP sensor voltage is less than .5 volt, go to next step. If TP sensor voltage is .5 volt or more, go to step 9).
  8. Connect at test light between 5-volt reference circuit and signal circuit terminals at TP sensor harness connector. If scan tool voltage is about 5 volts, go to step 11). If voltage is not about 5 volts, go to step 10).
  9. Check TP signal circuit for short to voltage. Check TP sensor ground circuit for high resistance between PCM and TP sensor. Check TP sensor ground circuit for poor connection. Repair as necessary. After repair is completed, go to step 13). If circuits are okay, go to step 12).
  10. Check TP sensor signal circuit or 5-volt reference circuit for high resistance between PCM and TP sensor. Check TP sensor signal circuit or 5-volt reference circuit for a poor connection. Repair as necessary. After repair is completed, go to step 13). If circuit is okay, go to next step.
  11. Replace TP sensor. After repair is completed, go to step 13).
  12. Replace PCM. Program replacement PCM using required equipment. After repair is completed, go to next step.
  13. Using scan tool, select CLEAR INFO or CLEAR DTCS function to 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 DTC P0121. If scan tool indicates FAILED THIS IGN, repeat step 2). If scan tool does not indicate FAILED THIS IGN, repair is complete.
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