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Home >> Geo >> 1996 >> Prizm Base, Automatic >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Tests >> DTC P0121 - Throttle Position (TP) Sensor Circuit Performance >> Diagnosis & Repair

Diagnosis & Repair

  1. Connect scan tool to DLC. Turn ignition on. Select TP sensor angle parameter on scan tool. Monitor scan tool while depressing accelerator pedal several times. If TP sensor value varies steadily between 10-80 percent, go to next step. If TP sensor value is not as specified, or reading is erratic, go to step 3).
  2. Select CLEAR INFORMATION function. Using scan tool, place vehicle into CHECK MODE. Operate vehicle within FREEZE FRAME conditions. If DTC P0121 resets, go to next step. If DTC P0121 does not reset, check for an intermittent problem. See TESTS W/O CODES article.
  3. Disconnect TP sensor harness connector. Select TP angle on scan tool. 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 reference voltage circuit (Yellow wire) and TP sensor input circuit (Light Green wire) at TP sensor harness connector. Monitor TP sensor on scan tool. If TP sensor value is greater than 90 percent, go to step 7). If TP sensor value is not as specified, go to step 6).
  5. Check TP sensor input circuit (Light Green wire) for short to power. Check TP sensor ground circuit (Brown wire) for open between TP sensor and PCM. Check TP sensor harness connector for proper connection. Repair as necessary. If no problems were found, replace PCM. Retest system.
  6. Check TP sensor input circuit (Light Green wire) for open or short. Check TP sensor reference voltage circuit (Yellow wire) for high resistance between TP sensor and PCM. Repair as necessary. If no problems were found, replace PCM. Retest system.
  7. Check TP sensor adjustment. See THROTTLE POSITION (TP) SENSOR in ADJUSTMENTS article. Repair as necessary. If adjustment is okay, replace TP sensor. Retest system.
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