LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Suzuki >> 2003 >> XL-7 Base, 4WD >> Repair and Diagnosis >> External Pages >> Different car >> Section 4 (Engine Controls - Self-Diagnostics) >> Diagnostic Tests >> DTC P0171: Bank 1 Fuel Trim System Lean >> Diagnostic Procedure
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnostic Procedure

WARNING: This page is about a different car, the 2002 Isuzu Trooper. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform ON-BOARD DIAGNOSTIC II SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing OBD-II system check, go to next step.
  2. If any DTCs other than P0171 and P0174 are set, diagnose them first before proceeding. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no other DTCs are set, go to next step.
  3. Using scan tool, observe BANK 1 L.T. FUEL TRIM values. While operating vehicle within CODE ENABLE CRITERIA  conditions. If L.T. FUEL TRIM value is 20 percent or more, go to step  5. If value is less than 20 percent, go to next step.
  4. Using scan tool, read and record FAIL RECORDS data. Clear DTCs and operate vehicle within CODE ENABLE CRITERIA  conditions. On scan tool, monitor DTC information. If scan tool indicates DTC P0171 FAILED THIS IGNITION, go to next step. If scan tool display is not as specified, and a lean condition is not present but driveability problem exists, repair by symptom. See TROUBLE SHOOTING - NO CODES article.
  5. If DTC P0174 is also set, go to next step. If DTC P0174 is not set, go to step  15.
  6. Check vacuum hoses for splits, kinks and proper routing. If problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  7. Check PCV valve for proper installation. If problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  8. Check MAF inlet screen for damage or foreign objects which may partially block airflow sample through MAF sensor. If problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  9. Start engine. If a high or unsteady idle condition is present, go to next step. If idle is okay, go to step  11.
  10. Check throttle body, intake manifold, and EGR valve system for vacuum leaks. If problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  11. Check for fuel contamination. If problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  12. Disconnect PCM 80-pin harness connectors E-21 (Blue) and E-22 (Red). PCM is located at right rear of engine compartment. Check fuel injector, power and sensor ground circuits for clean and tight connections at PCM harness connector. See WIRING DIAGRAMS article. If problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  13. Disconnect MAF sensor 3-pin harness connector E-7. Using scan tool, observe BANK 1 S.T. FUEL TRIM values while operating vehicle within CODE ENABLE CRITERIA  conditions. If BANK 1 S.T. FUEL TRIM values decreases to about zero percent, go to step  19. If value does not decrease as specified, go to next step.
  14. Perform FUEL SYSTEM PRESSURE TEST under BASIC FUEL SYSTEM CHECKS in BASIC DIAGNOSTIC PROCEDURES article. If problem with fuel system is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  15. Check intake manifold, fuel injector "O" rings, EGR adapter, EGR valve and EGR feed pipes for vacuum leaks. If problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  16. Check exhaust system for leaks, corrosion, loose or missing hardware. If problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, go to next step.
  17. Perform FUEL INJECTOR BALANCE TEST under FUEL SYSTEM in SYSTEM & COMPONENT TESTING article. If problem with fuel injectors is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC 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 problem is found, repair as necessary. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM. If no problem is found, check for an intermittent problem. See DIAGNOSTIC AIDS .
  19. Replace MAF sensor. After repair is complete, see VERIFYING VEHICLE REPAIR  under SELF-DIAGNOSTIC SYSTEM.
scientia non olet · About LEMON Manuals