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Home >> Isuzu >> 1997 >> Rodeo LS, 2.6 E >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls - Tests W/Codes - 2.6L >> Circuit Testing >> DTC P0171 - Fuel Trim System Lean >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) System Check. See BASIC TESTING article. Go to next step.
  2. If any DTCs other than P0171 are set, diagnose affected DTCs before proceeding. If no other DTCs are set, go to next step.
  3. Operate vehicle in closed loop mode while using scan tool to read LT FUEL TRIM values. If LT FUEL TRIM value is about 20 percent, go to step 5). If values are not as specified, go to next step.
  4. Using scan tool, read and record FAIL RECORDS data. Clear DTCs and operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until DTC P0171 test runs. If scan tool displays DTC P0171 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0171 FAILED THIS IGN, go to DIAGNOSTIC AIDS  .
  5. Check vacuum hoses for splits, kinks and proper routing. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
  6. Check PCV valve for proper installation. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
  7. Start engine. If high or unsteady idle condition exists, go to next step. If Idle is okay, go to step 10).
  8. Using scan tool, read IDLE AIR CONTROL (IAC) value. If value is more than 5 counts, go to step 10). If value is 5 counts or less, go to next step.
  9. Check throttle body, intake manifold, and EGR valve for vacuum leaks. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
  10. Check IAC valve for proper operation. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
  11. Check for fuel contamination. If fuel is contaminated, repair condition causing contamination. Retest system. If fuel is okay, go to next step.
  12. Check PCM injector, power and sensor grounds for clean and tight connection, and for proper location. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
  13. Perform FUEL SYSTEM PRESSURE TEST under BASIC FUEL SYSTEM CHECKS in BASIC TESTING article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
  14. Perform EVAP SYSTEM CHECK. See FUEL EVAPORATION CONTROL, under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM/COMPONENT TESTS article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
  15. Check intake manifold, injector "O" rings, EGR adapter, EGR valve, and EGR feed pipes for vacuum leaks. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
  16. Check exhaust system for leaks, loose or missing hardware. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
  17. Perform, INJECTOR BALANCE TEST under FUEL SYSTEM in SYSTEM/COMPONENT TESTS article. If a problem is found, repair as necessary. Retest system. If no problem is found, go to next step.
  18. Ensure HO2S is installed securely, and connector and harness are not contacting exhaust manifold or ignition wires. If a problem is found, repair as necessary. Retest system. If no problem is found, go to DIAGNOSTIC AIDS  .
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