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Home › Chevrolet › 1998 › Tracker 2D Utility, RWD, Standard › Repair and Diagnosis › Engine Performance › System › Engine Controls - Tests W/Codes › Diagnostic Trouble Codes › DTC P0121: Throttle Position (TP) Sensor System Performance › Diagnostic Test

Diagnostic Test

  1. If powertrain OBD system check has been performed, go to next step. If powertrain OBD system check has not been performed, perform powertrain OBD system check. See POWERTRAIN OBD SYSTEM CHECK  .
  2. Turn ignition switch to RUN position. Use scan tool to clear information function. Operate vehicle within freeze frame conditions. If DTC P0121 is displayed, go to next step. If DTC P0121 is not displayed, check the follow and repair as necessary:
    • Connection at PCM and TP sensor.
    • Damaged wiring harness.
    • TP sensor. See SENSOR RANGE CHARTS article.
  3. Start engine. Allow engine to reach normal operating temperature. Turn ignition switch to LOCK position. Disconnect TP sensor harness connector. Measure resistance between terminals No. 1 (Gray/Yellow wire) and No. 4 (Gray/Red wire) at TP sensor. See Fig 1 . If resistance is 3500-6500 ohms, go to next step. If resistance is not 3500-6500 ohms, go to step 8).
  4. Ensure throttle plate is closed. Measure resistance between terminals No. 1 (Gray/Yellow wire) and No. 3 (Gray wire) at TP sensor. If resistance is .3-2000 ohms, go to next step. If resistance is not .3-2000 ohms, go to step 8).
  5. Open throttle to wide open. Measure resistance between terminals No. 1 (Gray/Yellow wire) and No. 3 (Gray wire) at TP sensor. If resistance is 2000-6500 ohms, go to next step. If resistance is not 2000-6500 ohms, go to step 8).
  6. Insert a .020" (0.5 mm) feeler gauge between throttle lever and throttle stop screw. Measure resistance between terminals No. 1 (Gray/Yellow wire) and No. 2 (Blue/White wire) at TP sensor. If resistance is 0-500 ohms, go to next step. If resistance is not 0-500 ohms, go to step 8).
  7. Insert a .031" (0.8 mm) feeler gauge between throttle lever and throttle lever stop screw. Measure resistance between terminals No. 1 (Gray/Yellow wire) and No. 2 (Blue/White wire) at TP sensor. If resistance is not infinite, go to next step. If resistance is infinite, go to step 9).
  8. Adjust or replace TP sensor as necessary and go to step 10).
  9. Replace PCM and go to next step.
  10. Test drive vehicle under conditions that set the DTC. Check for other DTCs. If DTCs were retrieved, perform appropriate DTC test. If no DTCs were retrieved, system is okay at this time.
Fig 1: Identifying Throttle Position Sensor Terminals
G98C00853Courtesy of GENERAL MOTORS CORP.
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