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Home >> Isuzu >> 1996 >> Hombre S >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Testing >> DTC P0172 - Fuel Trim System Rich >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) System Check. After performing OBD 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 70), go to step 5). If fuel trim index is greater than 70, 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 as possible. If fuel trim index is less than 70, go to step 21). If fuel trim index is greater than 70, 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 repair is completed, go to step 21). If air intake duct is okay, go to next step.
  7. Inspect throttle body inlet from damage of foreign objects that may partially block airflow. Repair as necessary. After repair is completed, go to step 21). If no repair is necessary, go to next step.
  8. Inspect throttle body bore, throttle plate and IAC passages for coking and foreign objects. Repair as necessary. After repair is completed, 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 idle is not low or unstable, 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 100 or more, go to next step.
  11. Disconnect MAP sensor connector. Start and warm engine to normal operating temperature. Ensure system is in closed loop. Using scan tool, select FUEL TRIM INDEX display. If fuel trim index is more than 70, go to step 20). If fuel trim index is less than 70, go to next step.
  12. Go to DTC P0506 or P0507 to check IAC valve performance. Repair as necessary. After repair is completed, 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 repair is completed, 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 THROTTLE 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 BASIC FUEL SYSTEM CHECKS (A-7) in BASIC TESTING article. Repair fuel system as necessary. After repair is completed, go to step 21) If fuel system is okay, go to next step.
  16. Check fuel evaporation system for proper operation. Ensure canister purge solenoid is functioning properly. See SYSTEM/COMPONENT TESTS article. Repair as necessary. After repair is completed, 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 TESTS article. Repair as necessary. After repair is completed, go to step 21). If no problems are found, go to next step.
  18. Remove and inspect Oxygen Sensor 1 (O2S 1) for silicon contamination. If contamination exists, a powdery White deposit on portion of sensor exposed to exhaust system will be present. If silicon contamination is present, locate and repair source of contamination. Replace O2S 1. After repair is completed, go to step 21). If no contamination exists, go to 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 repair is completed, go to step 21).
  20. Replace MAP sensor. After repair is completed, 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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