LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Chevrolet >> 2000 >> Venture Plus >> Repair and Diagnosis >> Engine Performance >> System >> Engine Controls Self-Diagnostics >> Diagnostic Tests >> DTC P0171: Fuel Trim System Lean >> Diagnostic Procedures
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing OBD system check, go to next step.
  2. If any other DTCs 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 and ST FUEL TRIM values. If LT FUEL TRIM value is about +16 percent and ST 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 FAILURE RECORDS data. Clear DTCs and operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until DTC P0171 test runs. If scan tool indicates that DTC P0171 failed this ignition, go to next step. If scan tool does not indicate that DTC P0171 failed this ignition, see DIAGNOSTIC AIDS .
  5. Check vacuum hoses for splits, kinks and proper routing. If a problem is found, repair as necessary. After repairs, go to step  22. If no problem is found, go to next step.
  6. Check PCV valve for proper installation. If a problem is found, repair as necessary. After repairs, go to step  22. If no problem is found, go to next step.
  7. Check throttle body inlet screen for blockage or foreign objects which may partially block airflow sample through MAF sensor. If a problem is found, repair as necessary. After repairs, go to step  22. If no problem is found, go to next step.
  8. Start engine. If high or unsteady idle condition exists, go to next step. If Idle is okay, go to step  11.
  9. Using scan tool, read IDLE AIR CONTROL (IAC) value. If value is greater than 5 counts, go to step  11. If value is not greater than 5 counts, go to next step.
  10. Check throttle body, intake manifold, and EGR valve for vacuum leaks. If a problem is found, repair as necessary. After repairs, go to step  22. If no problem is found, go to next step.
  11. Check IAC valve for proper operation. If a problem is found, repair as necessary. After repairs, go to step  22. If no problem is found, go to next step.
  12. Check for fuel contamination. If fuel is contaminated, repair condition causing contamination. After repairs, go to step  22. If fuel is okay, go to next step.
  13. Check PCM injector, power and sensor grounds for clean and tight connection, and for proper location. If a problem is found, repair as necessary. After repairs, go to step  22. If no problem is found, go to next step.
  14. Disconnect MAF sensor harness connector. Operate vehicle in closed loop mode while monitoring scan tool ST FUEL TRIM. If ST FUEL TRIM decreases to about zero percent, go to step  21. If ST FUEL TRIM does not decrease to about zero percent, go to next step.
  15. Check fuel pressure. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article. If a problem is found, repair as necessary. After repairs, go to step  22. If no problem is found, go to next step.
  16. Perform EVAP system check. See EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article. If a problem is found, repair as necessary. After repairs, go to step  22. If no problem is found, go to next step.
  17. 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. After repairs, go to step  22. If no problem is found, go to next step.
  18. Check exhaust system for corrosion, loose or missing hardware. If a problem is found, repair as necessary. After repairs, go to step  22. If no problem is found, go to next step.
  19. Perform INJECTOR BALANCE TEST. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. If a problem is found, repair as necessary. After repairs, go to step  22. If no problem is found, go to next step.
  20. 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. After repairs, go to step  22. If no problem is found, see DIAGNOSTIC AIDS .
  21. Replace MAF sensor. After replacing sensor, go to next step.
  22. Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for this DTC. If scan tool indicates that this DTC failed this ignition, go to step  2. If scan tool does not indicate that this DTC failed this ignition, system is okay.
scientia non olet · About LEMON Manuals