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Home >> Isuzu >> 1999 >> Trooper Part Time >> Repair and Diagnosis (Single Page) >> Engine Performance >> System >> Engine Controls - Self-Diagnostics >> Diagnostic Trouble Code Identification >> DTC P0121: Throttle Position (TP) Sensor Circuit Performance >> Diagnostic Aids
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Diagnostic Aids

An intermittent problem can be caused by misrouted harness, rubbed-through wire insulation or broken wire inside insulation.

Low MAP reading can cause PCM to incorrectly calculate TP sensor value. If DTC cannot be duplicated, check scan tool FAILURE RECORDS to determine mileage since last DTC was set. If it is determined that DTC is intermittent, performing DTCs P1121 and DTC P1122 diagnostics may isolate cause of fault.

  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  5.
  3. Turn ignition off. Disconnect MAP sensor harness connector. Connect a test light between MAP sensor voltage reference circuit (Green/White wire) and MAP sensor signal circuit (Red wire on VehiCROSS, Gray wire on 3.2L, or Green/White wire on all others) 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 (Green wire). Repair as necessary. If wire is okay, replace PCM. 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 voltage 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 (Blue wire) shorted to power.
    • High resistance in TP sensor ground (Green wire) circuit.

    Repair as necessary. If no problems are found, replace PCM. Retest system.

  9. Check for the following items:
    • Poor connection in TP sensor signal circuit (Blue wire) or voltage reference circuit (Red wire).
    • High resistance in TP sensor voltage reference circuit (Red wire).

Repair as necessary. If no problems are found, replace PCM. Retest system.

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