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Home >> Geo >> 1997 >> Metro Base >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Controls - Tests W/Codes 1.0 & 1.3L >> Diagnostic Trouble Code Tests >> DTC P0121 - Throttle Position Sensor System Performance >> Diagnosis & Repair

Diagnosis & Repair

  1. Ensure engine is at normal operating temperature. Turn ignition on. Insert a.14" (3.5 mm) feeler gauge between throttle lever and throttle stop screw. Using a voltmeter, backprobe between ground and TP sensor signal circuit (Light Green/White wire) at PCM connector. If TP sensor value is.2-1.1 volts with feeler gauge, and 2.8-4.8 volts at WOT, check for an intermittent problem. See the TESTS W/O CODES article. If voltage is not as specified, go to next step.
  2. Disconnect TP sensor electrical connector. Using a voltmeter, backprobe between TP sensor signal circuit at PCM 16-pin connector terminal No. 9 (Light Green/White wire) and ground. If voltage is 4-5 volts, go to next step. If voltage is not as specified, go to step 4).
  3. Using a voltmeter, measure voltage of TP sensor signal circuit at TP harness connector terminal No. 4 (Light Green/White wire). If voltage is 4-5 volts, adjust or replace TP sensor. If voltage is not as specified, check for open Light Green/White wire. Repair as necessary. If wire is okay, replace PCM. After repair is completed, go to step 5).
  4. Check TP sensor signal circuit (Light Green/White wire) for short to voltage, or short to ground. If TP sensor signal circuit is okay, check TP sensor ground circuit (Light Green/Black wire) for a poor connection. Repair as necessary. If TP sensor circuits are okay, replace PCM. If repair is necessary, go to next.
  5. 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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