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Home >> Isuzu >> 1996 >> Hombre S >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes >> Circuit Testing >> DTC P0171 - Fuel Trim System Lean >> 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 165, go to next step. If fuel trim index is greater than specification, go to step 5).
  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 165, go to step 16). If fuel trim index is greater than specification, go to next step.
  5. Check vacuum hoses for splits, kinks and proper routing. Check PCV valve for proper installation. Check for fuel contamination. Check PCM and sensor grounds. Check O2S 1 for correct installation and ensure O2S 1 wiring is not in contact with exhaust manifold. If no problems are found, go to next step. If any problem is found, go to step 7).
  6. Disconnect MAP sensor connector. Operate vehicle in closed loop while monitoring FUEL INDEX TRIM. If fuel trim index is greater than specification, go to step 9). If fuel trim index is less than 165, go tostep 16).
  7. Repair fault that was detected in step 5). Operate vehicle in closed loop while monitoring FUEL INDEX TRIM. If fuel trim index is greater than 165, go to step 9). If fuel trim index is less than 165, go to next step.
  8. Lean condition is not present at this time. If a driveability problem exists, go to TESTS W/O CODES article. If no driveability problem exist, go to step 16).
  9. Check vacuum hoses for splits, kinks and proper routing. Check throttle body, intake manifold and injector "O" rings for vacuum leaks. Repair as necessary. After repair is completed, go to step 16). If no repairs are necessary, go to next step.
  10. Start engine and allow it to idle. Using scan tool, check IAC count. If IAC count is more than 5, go to next step. If IAC count is 5 or less, go to step 12).
  11. Check for fuel contamination. Repair as necessary. After repair is completed, go to step 16). If fuel is okay, go to step 13).
  12. Go to DTC P0506 or P0507 to check IAC valve performance. Repair as necessary. After repair is completed, go to step 16). If IAC valve is okay, go to next step.
  13. Connect a fuel pressure gauge to fuel system. Cycle ignition switch 2-3 times. With fuel pump running, observe fuel pressure. If fuel pressure is 41-47 psi (284-325 kPa), go to next step. If fuel pressure is not 41-47 psi (284-325 kPa), repair fuel system as necessary. See SYSTEM/COMPONENT TESTS article.
  14. Ensure engine is at normal operating temperature. Start engine and allow it to idle. Observe fuel pressure. Fuel pressure that is noted in step 13) should drop 3-10 psi (21-69 kPa). If fuel pressure is as specified, perform injector balance test. See FUEL SYSTEM in SYSTEM/COMPONENT TESTS article. If fuel pressure is not as specified, see BASIC FUEL SYSTEM CHECKS (A-7) in BASIC TESTING article.
  15. Replace MAP sensor. After repair is completed, go to next step.
  16. 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 P0171. 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).
  17. If any other DTCs are set, diagnose DTCs as necessary. If no other DTCs are set, no problem is indicated at this time. See DIAGNOSTIC AIDS.
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