LEMON Manuals: Even more car manuals for everyone
Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 370 (Engine Control System - Self-Diagnostics - 4.2L) >> Diagnostic Tests >> DTC P0171: Fuel Trim System - Lean (Bank 1) >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Oldsmobile Bravada, 2003 GMC Envoy XL, 2003 GMC Envoy, and 2003 Chevrolet TrailBlazer. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
    2. NOTE: If any DTCs are set, other than P0171, refer to affected DTCs before continuing. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  2. Connect scan tool. Start engine and drive vehicle under normal conditions until the engine reaches operating temperature and is in closed loop. Turn engine off. Turn ignition on, with engine off. Review the Freeze Frame Records/Failure Records and record displayed data for this DTC. Does scan tool indicate that the Fuel Trim Index is greater than 20 percent? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  3. Operate engine at idle. Using scan tool, observe the O2S parameters. Does scan tool indicate that the values are 200-800 mv and fluctuating? If yes, go to next step. If no, go to step  6.
  4. Turn engine off. Inspect the following items:
    • Vacuum hoses for splits, kinks, and proper connections.
    • If fuel pressure is too low, this DTC may set.
    • Fuel contamination.

    Did you find and correct the condition? If yes, go to step  8. If no, go to step  7.

  5. Turn engine off. Turn ignition on, with engine off. Observe the MAP sensor pressure parameter with scan tool. Refer to Altitude vs. Barometric Pressure table in SENSOR OPERATING RANGE CHARTS - TRUCKS article. The MAP sensor pressure should be within the range specified for your altitude. Does the MAP indicate the correct barometric pressure? If yes, go to next step. If no, go to DTC P0105: MAP SENSOR CIRCUIT - INSUFFICIENT ACTIVITY .
  6. Turn engine off. Inspect O2S for proper installation. Ensure electrical connectors and wires are secured and not contacting the exhaust system. Check for short between the signal circuit and low reference circuit. Did you find and correct the condition? If yes, go to step  8. If no, diagnose fuel system. See FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.2L BRAVADA, ENVOY, ENVOY XL, TRAILBLAZER & TRAILBLAZER EXT article.
  7. Operate engine at idle. Check for missing, loose, or leaking exhaust components. Check for vacuum leaks at the intake manifold, throttle body, and injector "O" rings. Check the air induction system and air intake ducts for leaks. Check crankcase ventilation system for leaks. Did you find and correct the condition? If yes, go to next step. If no, see appropriate article in ENGINES.
    8. NOTE: After repairs, use scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim.
  8. Clear the DTCs with scan tool. Turn ignition off for 30 seconds. Start engine. Operate vehicle within the Conditions For Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  9. Observe the stored information, Capture Info with scan tool. Does scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
scientia non olet · About LEMON Manuals