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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 116 (Engine Controls - Self-Diagnostics - 4.0L) >> Diagnostic Tests >> DTC P0171 & P0174: Fuel Trim System Lean, Bank 1 & 2 >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Oldsmobile Aurora. 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, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
    2. NOTE: If any other DTCs are set, repair DTCs before continuing with this test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  2. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Using scan tool, record Long Term Fuel Trim data. Turn ignition off. Turn ignition on. Using scan tool, review Freeze Frame Records and/or Failure Records and record data. Does the scan tool indicate that the Long Term Fuel Trim is greater than 23 percent? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  3. Start engine and allow it to idle. Using scan tool, observe HO2S voltage. Does the scan tool indicate that the values are within 200-800 mV and fluctuating? If yes, go to next step. If no, go to step  5.
  4. Turn ignition off. Visually and physically inspect the following items:
    • Vacuum hoses for splits, kinks, and proper connections.
    • Ensure that the vehicle has sufficient fuel in the tank. If the 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 engine off. Inspect HO2S for proper installation. Ensure that the electrical connectors and the wires are secured and not contacting the exhaust system. Inspect for a 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 FUEL SYSTEMS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  6. Operate engine at idle. Check for missing, loose, or leaking exhaust components. Check for vacuum leaks at intake manifold, throttle body and injector "O" rings. Check 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, check engine mechanical condition and repair as necessary.
  7. After repairs, using scan tool fuel trim reset function, reset long term fuel trim. Use the scan tool in order to clear the DTCs. 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. With a scan tool, observe the stored information, Capture Info. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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