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Home >> Geo >> 1996 >> Prizm Base, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Tests >> DTC P0120 - Throttle Position (TP) Sensor Circuit >> Diagnosis & Repair

Diagnosis & Repair

  1. Connect scan tool to DLC. Ensure throttle is closed. Select TP sensor parameter on scan tool. If TP sensor value is greater than 25 percent, go to step 4). If TP sensor value is not as specified, go to next step.
  2. Monitor TP sensor with throttle closed. If TP sensor value is less than 6 percent, go to step 11). If TP sensor value is not as specified, go to next step.
  3. Select CLEAR INFORMATION function. Using scan tool, place vehicle into CHECK MODE. Operate vehicle within FREEZE FRAME conditions. If DTC P0120 resets, repeat step 1). If DTC P0120 does not reset, check for an intermittent problem. See TESTS W/O CODES article.
  4. Turn ignition off. Disconnect TP sensor harness connector. Turn ignition on. Monitor TP sensor on scan tool. If TP sensor value is greater than zero percent, go to step 6). If TP sensor value is not as specified, go to next step.
  5. Using a test light connected to battery voltage, probe TP sensor ground circuit (Brown wire) at harness connector. If test light comes on, go to step 7). If test light does not come on, go to step 9).
  6. With ignition off, disconnect PCM harness connector. Turn ignition on. Check TP sensor input circuit (Light Green wire) for short to power. Repair as necessary. If wire is okay, replace PCM. Retest system.
  7. Turn ignition on. Using a voltmeter, measure voltage of TP sensor reference voltage circuit (Yellow wire) between harness connector and ground. If reading is 5 volts, go to next step. If reading is not as specified, go to step 10).
  8. Check for poor connections at TP sensor and PCM harness connectors. Repair as necessary. Retest system. If connections are okay, go to step 17).
  9. Turn ignition off. Disconnect PCM harness connector. Check for open TP sensor ground circuit (Brown wire). Repair as necessary. If wire is okay, replace PCM. Retest system.
  10. Turn ignition off. Disconnect PCM harness connector. Check TP sensor reference voltage circuit (Yellow wire) for open or short. Repair as necessary. If wire is okay, replace PCM. Retest system.
  11. Disconnect TP sensor harness connector. Using a fused jumper wire, connect Light Green wire and Yellow wire together at TP sensor harness connector. Select TP sensor on scan tool. If TP sensor value is greater than 90 percent, go to step 17). If TP sensor value is not as specified, go to next step.
  12. Connect a test light to battery positive terminal and probe TP sensor input circuit (Light Green wire) at harness connector. Monitor TP sensor on scan tool. If TP sensor value is greater than 90 percent, go to next step. If TP sensor value is not as specified, go to step 15).
  13. Turn ignition off. Disconnect PCM harness connector. Check TP sensor reference voltage circuit (Yellow wire) for open or short. Repair as necessary. Retest system. If wire is okay, go to next step.
  14. Check reference voltage circuit (Yellow wire) for poor connections at TP sensor and PCM. Repair as necessary. If connections are okay, replace PCM. Retest system.
  15. Turn ignition off. Disconnect PCM connector. Check TP sensor input circuit (Light Green wire) for open or short to ground. Repair as necessary. Retest system. If wire is okay, go to next step.
  16. Check TP sensor input circuit (Light Green wire) for poor connection at PCM. Repair as necessary. If wire is okay, replace PCM. Retest system.
  17. 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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