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Home >> Isuzu >> 2000 >> Trooper S, 4WD, Part Time >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Controls - Self-Diagnostics - 3.2L & 3.5L >> Diagnostic Trouble Code Identification >> DTC P0121: Throttle Position (TP) Sensor Circuit Performance >> Diagnostic Procedure
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Diagnostic Procedure

  1. Perform On-Board Diagnostic (OBD) System Check. See BASIC DIAGNOSTIC PROCEDURES article. Go to next step.
  2. Turn ignition on. Observe MAP sensor parameter on scan tool. If display is less than 65 kPa, go to next step. If display is not as specified, go to step  6.
  3. Turn ignition off. Disconnect MAP sensor harness connector. Connect a test light between MAP sensor 5-volt reference circuit and MAP sensor signal circuit at harness connector. Turn ignition on. If display on scan tool is less than 65 kPa, replace MAP sensor. Retest system. If display is not as specified, go to next step.
  4. Turn ignition off. Check for an open, short to ground or short to MAP sensor ground circuit. Repair as necessary. If wire is okay, replace and reprogram PCM. See PROGRAMMING . Retest system.
  5. Observe TP sensor angle on scan tool while slowly opening throttle. If display shows a steady increase from zero percent to 100 percent, check for an intermittent problem. See DIAGNOSTIC AIDS . If display is not as specified, go to next step.
  6. Turn ignition off. Disconnect TP sensor harness connector. Turn ignition on. Observe TP sensor parameter on scan tool. If display is zero volts, go to next step. If display is not as specified, go to step  8.
  7. Turn ignition off. Connect a test light between 5-volt reference circuit (Red wire) and sensor signal circuit (Blue wire) at TP sensor harness connector. Turn ignition on. If display is 5 volts, replace TP sensor. Retest system. If display is not as specified, go to step  9.
  8. Check for the following items:
    • TP sensor signal circuit shorted to voltage.
    • High resistance or open in TP sensor ground circuit.

    Repair as necessary. If no problems are found, replace and reprogram PCM. See PROGRAMMING . Retest system.

  9. Check for the following items:
    • Poor connection in TP sensor signal circuit or 5-volt reference circuit.
    • High resistance in TP sensor 5-volt reference circuit.

Repair as necessary. If no problems are found, replace and reprogram PCM. See PROGRAMMING . Retest system.

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