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Home >> Isuzu >> 2001 >> VehiCROSS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Self-Diagnostics - 3.2L & 3.5L >> Self-Diagnostic System >> Electric Throttle Control System Check >> Diagnostic Procedure

Diagnostic Procedure

  1. Perform ON-BOARD DIAGNOSTIC II SYSTEM CHECK . After performing OBD-II system check, go to next step.
  2. Check for throttle body tampering, restricted or collapsed air intake duct, restricted air filter or any foreign objects blocking air intake system. Check for any objects blocking throttle passage or throttle bore, excessive deposits in throttle passage or on throttle plate. Check for smooth movement of throttle lever. Throttle spring should not bind or have excessive play. Throttle lever should move with only 9 INCH Lbs (1.0 N.m) of force applied. Turn ignition on and ensure that throttle lever operation is smooth when accelerator pedal is depressed. Repair as necessary. If no problems were found, go to next step.
  3. Check for accelerator pedal tampering or objects that may block free movement of pedal. Check for smooth accelerator pedal, and ensure that pedal arm does not have excessive free play. Repair as necessary. If no problems were found, go to next step.
  4. Check for loose or poor connections at throttle body harness or Acceleration Position Sensor (APS) harness connectors. Repair any problems found as necessary. Retest system. If no problems were found, go to next step.
  5. Use DVOM to check for open, short circuit to ground or voltage, or high resistance in throttle valve DC motor electrical circuit between DC motor and PCM. Check resistance of DC motor. DC motor resistance should be between 0.3 and 100 ohms. If faulty circuit or high resistance in DC motor is present, repair or replace as necessary. Retest system. If no problems were found, go to next step.
    NOTE: Varying APS sensor values are checked by depressing gas pedal.
  6. Turn ignition on, engine off. Using scan tool, check values for all Throttle Position Sensor (TPS) and Acceleration Position Sensor (APS). At idle, APS1 should be 11-13 percent, APS2 and APS3 should be 87-88 percent, TPS1 should be 3-13 percent, and TPS2 should be 87-89 percent. At WOT, APS1 should be 85-89 percent, APS2 should be 11-15 percent, APS3 should be 32-36 percent, TPS1 should be 87-89 percent, and TPS2 should be 3-13 percent. Ensure that all sensor resistance values change smoothly as throttle position goes from closed to WOT. If problems were not found, go to next step. If any problems were found with any TPS or APS readings, go to step  10.
    NOTE: Varying APS sensor values are checked by depressing gas pedal.
  7. Replace throttle body. Go to step  3.
  8. Check for open circuit, short to voltage and/or ground or poor connection at PCM of following circuits:
    • APS circuit 1.
    • APS circuit 2.
    • APS circuit 3.
    • APS resistance.

    If problem is present, repair as necessary. Go to step  11. If problem is not present, go to next step.

  9. Replace Accelerator Position Sensor (APS).
  10. Check for stored DTC's P1125, P1290, P1295 or P1299. See appropriate DTC under DIAGNOSTIC TESTS . Repair as necessary. If problem is still present, go to next step.
  11. Repair any opens, short to voltage, short to ground or poor connections found in any APS electrical circuits. Retest system.
  12. Check for DTCs P1271, P1272, P1273, P1514, P1515, P1516 or P1523. If any DTCs are present, see appropriate DTC under DIAGNOSTIC TESTS . Repair as necessary. If DTCs are not present, go to next step.
  13. Replace and reprogram PCM. See EEPROM PROGRAMMING PROCEDURE  under PROGRAMMING.
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