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Home >> Geo >> 1996 >> Metro Base, 4D Sedan, Standard >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Tests >> DTC P0121 - Throttle Position Sensor System Performance >> Diagnosis & Repair
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Diagnosis & Repair

  1. Ensure engine is at normal operating temperature. Turn ignition on. Insert a .140" (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 0.2-1.1 volts with feeler gauge, and 2.8-4.8 volts at WOT, check for an intermittent problem. See TESTS W/O CODES article. If voltage is not as specified, go to next step.
  2. Disconnect TP sensor connector. Observe voltmeter while backprobing between ground and TP sensor signal circuit (Light Green/White wire) at PCM connector. If reading is 4-5 volts, go to next step. If reading is not as specified, go to step 4).
  3. Using a voltmeter, measure voltage of TP sensor signal circuit (Light Green/White wire) at TP harness connector. If reading is 4-5 volts, adjust or replace TP sensor. If reading is not as specified, check for open Light Green/White wire. Repair as necessary. If wire is okay, replace PCM. Retest system.
  4. Check TP sensor signal circuit (Light Green/White wire) for poor connection, short to power, or short to ground. Repair as necessary. If TP sensor signal circuit is okay, replace PCM. Retest system.
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