LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Pontiac >> 2002 >> Aztek AWD >> 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. 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 those DTCs before continuing. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  2. Connect the scan tool. Start and idle engine at the normal operating temperature in closed loop. Record the long term fuel trim. Turn OFF the engine. Turn ON the ignition, with the engine OFF. Review the Freeze Frame Records/Failure Records and record displayed data for this DTC. Does the scan tool indicate that the Fuel Trim Index is greater than 23%? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  3. Operate the engine at idle. Using the scan tool, observe the O2S parameters. Does the scan tool indicate that the values are 200-800 mv and fluctuating? If yes, go to next step. If no, go to step  5.
  4. Turn OFF the engine. Inspect the following items:
    • Vacuum hoses for splits, kinks, and proper connections.
    • Ensure that the vehicle has sufficient fuel in tank. If fuel pressure is too low, this DTC may set.
    • Fuel contamination.

    Did you find and correct the condition? If yes, go to step  7. If no, go to step  6.

  5. Turn OFF the engine. Check the HO2S for proper installation. Check to 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  7. If no, diagnose fuel system. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
  6. Operate the 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. Secondary Air Injection (AIR) system for leaks, improper air delivery, shut-off valve not closing. 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.
    7. NOTE: After any of the above repairs, use scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim.
  7. Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the 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.
  8. Observe the stored information, Capture Info with a scan tool. Does the 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