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HOMESERVICE MANUALSPONTIAC1997GRAND PRIX GTP, 4D SEDANREPAIR AND DIAGNOSISEXTERNAL PAGESDIFFERENT VARIANT/TRIMSECTION 1 (ENGINE CONTROLS - TESTS W/CODES - 3.1L ENGINE)DIAGNOSTIC TROUBLE CODESDTC P0121 - TP SENSOR SYSTEM PERFORMANCEDIAGNOSTIC PROCEDURES
1997 Pontiac Grand Prix GTP, 4D Sedan

Diagnostic Procedures

1997 Pontiac Grand Prix GTP, 4D SedanSECTION Diagnostic Procedures
WARNING: This page is about a different variant/trim than selected.
  1. Perform ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK. See the BASIC TESTING - 3.1L article. 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 not as specified, go to step 6).
  3. Disconnect MAP sensor harness connector. Connect a test light between the 5-volt reference circuit and signal circuit terminals at MAP sensor harness connector. If MAP sensor value is less than 95 kPa, go to step 5). If MAP sensor value is not less than 95 kPa, go to next step.
  4. Check for an open or short to ground in MAP sensor signal circuit. Repair as necessary. After repairs, go to step 13). If circuit is okay, go to step 12).
  5. Replace MAP sensor. After replacing sensor, 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 near zero volts, go to next step. If TP sensor voltage is not near zero volts, 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 repairs, 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 repairs, go to step 13). If circuit is okay, go to next step.
  11. Replace TP sensor. After replacing sensor, go to step 13).
  12. Replace PCM. Program replacement PCM using required equipment. After replacing PCM, 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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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.