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Diagnostic Procedures

WARNING: This page is about a different car, the 2000 Isuzu Hombre. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform On-Board Diagnostic II (OBD-II) system check. See ON-BOARD DIAGNOSTIC II (OBD-II) SYSTEM CHECK in SELF-DIAGNOSTICS - INTRODUCTION article. After performing OBD-II system check, go to next step.
  2. If any other DTCs are set, diagnose DTCs as necessary before proceeding. If no other DTCs are set, go to next step.
  3. Start and warm engine to normal operating temperature. Ensure system is in closed loop. Using scan tool, select FUEL TRIM INDEX. If fuel trim index is less than 80, go to step  5. If fuel trim index is not less than 80, go to next step.
  4. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME data, and note parameters. Start engine and operate vehicle within conditions required for setting this DTC, and as close to conditions recorded in FREEZE FRAME data as possible. If fuel trim index is less than 80, go to step  21. If fuel trim index is not less than 80, go to next step.
  5. Turn ignition off. Check air filter. Replace filter as necessary. After repair is completed, go to step  21. If air filter is okay, go to next step.
  6. Check for collapsed or restricted air intake duct. Repair as necessary. After repairs, go to step  21. If air intake duct is okay, go to next step.
  7. Inspect throttle body inlet for damage or foreign objects that may block airflow. Repair as necessary. After repairs, go to step  21. If no repair is necessary, go to next step.
  8. Inspect throttle body bore, throttle plate and IAC passages for carbon build up and foreign objects. Repair as necessary. After repairs, go to step  21. If no repair is necessary, go to next step.
  9. Start engine. Ensure all accessories are off. Note idle condition. If idle is low or unstable, go to next step. If not, go to step  12.
  10. Using scan tool, check IAC count. If IAC count is less than 100, go to step  12. If IAC count is not less than 100, go to next step.
  11. Disconnect MAP sensor connector. Start and warm engine to normal operating temperature. Ensure system is operating in closed loop. Using scan tool, select FUEL TRIM INDEX display. If fuel trim index is greater than 80, go to step  20. If fuel trim index is less than 80, go to next step.
  12. Go to DTC P0506: IAC SYSTEM RPM LOW  or DTC P0507: IAC SYSTEM RPM HIGH  to check IAC valve performance. Repair as necessary. After repairs, go to step  21. If IAC valve is okay, go to next step.
  13. Disconnect fuel pressure regulator vacuum hose. Check vacuum hose for presence of fuel. If fuel is present, replace fuel pressure regulator. After repairs, go to step  21. If fuel pressure regulator is okay, go to next step.
  14. Turn ignition on, with engine off. Using scan tool, monitor THROT POSITION display while slowly depressing accelerator pedal. If reading increases steadily from minimum voltage to maximum voltage at wide open throttle, go to next step. If reading does not increase steadily from minimum voltage to maximum voltage, go to step  19.
  15. Perform FUEL SYSTEM in BASIC DIAGNOSTIC PROCEDURES article. Repair fuel system as necessary. After repairs, go to step  21. If fuel system is okay, go to next step.
  16. Check fuel evaporation system operation. Ensure canister purge solenoid is functioning properly. See SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step  21. If fuel evaporation system is functioning properly, go to next step.
  17. Perform INJECTOR BALANCE TEST. See FUEL SYSTEM in SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step  21. If no problems are found, go to next step.
  18. Remove and inspect Oxygen Sensor 1 (O2S 1) for silicone contamination. If contamination exists, a powdery, white deposit on portion of sensor exposed to exhaust system will be present. If silicone contamination is present, locate and repair source of contamination. Replace O2S 1. After repair is completed, go to step  21. If no contamination exists, see DIAGNOSTIC AIDS .
  19. Check Throttle Position (TP) sensor mounting screws. Tighten or replace screws as necessary. After repair is completed, go to step  21. If mounting screws are okay, replace TP sensor. After replacing sensor, go to step  21.
  20. Replace MAP sensor. After replacing sensor, go to next step.
  21. Using scan tool, select CLEAR INFO or CLEAR DTCS function to clear DTCs. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Operate vehicle within conditions required for setting this DTC. Select SPECIFIC DTC function, then enter DTC P0172. If scan tool indicates TEST RAN AND PASSED, go to next step. If scan tool does not indicate TEST RAN AND PASSED, repeat step  2.
  22. If any other DTCs are set, diagnose DTCs as necessary. If no other DTCs are set, no problem is indicated at this time.
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