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Home >> Geo >> 1997 >> Prizm Base, Automatic >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Controls - Tests W/Codes 1.6 & 1.8L >> Diagnostic Tests >> DTC P0121 - Throttle Position (TP) Sensor Circuit Performance >> Diagnosis & Repair
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Diagnosis & Repair

  1. Connect scan tool to DLC. Turn ignition on and engine off. Using scan tool, select TP sensor angle parameter. Monitor scan tool while depressing accelerator pedal several times. If TP sensor value varies steadily between 10 percent (released position) and 80 percent (depressed position), go to next step. If TP sensor value is not as specified, or reading is erratic, go to step 3).
  2. Using scan tool, clear DTC information. Using scan tool, place vehicle into check mode. Operate vehicle within freeze frame conditions. If DTC P0121 sets, go to next step. If DTC P0121 does not set, go to DIAGNOSTIC AIDS. Check for an intermittent problem. See the TESTS W/O CODES article.
  3. Disconnect TP sensor electrical connector. Using scan tool, select TP sensor angle. If TP sensor value is greater than zero percent, go to step 5). If TP sensor value is not as specified, go to next step.
  4. Connect a test light between TP sensor connector terminals No. 3 (Light Green wire) and No. 4 (Yellow wire). Using scan tool, monitor TP sensor angle. If TP sensor value is 90 percent or less, go to step 6). If TP sensor value is greater than 90 percent, go to step 7).
  5. Check for a short to battery voltage in Light Green wire between TP sensor connector terminal No. 3 and PCM 16-pin connector terminal No. 11. Check for an open in Brown wire between TP sensor connector terminal No. 1 and PCM 16-pin connector terminal No. 9. Check TP sensor electrical connector for proper connection. Repair as necessary. If no problems were found, replace PCM. After repair is completed, go to step 8).
  6. Check for an open or short in Light Green wire between TP sensor connector terminal No. 3 and PCM 16-pin connector terminal No. 11. Check for high resistance between TP sensor connector terminal No. 4 and PCM 16-pin connector terminal No. 1. Repair as necessary. If no problems were found, replace PCM. After repair is completed, go to step 8).
  7. Check TP sensor adjustment. See THROTTLE POSITION (TP) SENSOR in the ADJUSTMENTS article. Repair as necessary. If adjustment is okay, replace TP sensor. After repair is completed, go to next step.
  8. After repairs, using scan tool, clear DTC information. Road test vehicle within freeze frame conditions that set DTC. Check for DTCs. If no DTCs are stored, repair is complete. If any DTCs are set, go to appropriate DTC diagnostic test.
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