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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 405 (Engine Controls - Self-Diagnostics) >> 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 2003 Cadillac Seville and 2003 Cadillac DeVille. 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 or P0174, refer to those DTCs before continuing. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  2. Install a scan tool. Start and idle the engine at normal operating temperature in Closed Loop. Record the Long Term Fuel Trim data. Turn engine off. Turn ignition on, with the engine off. Review the Freeze Frame/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. Observe the HO2S parameters with a scan tool. 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 engine off. 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 the engine off. 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 FUEL SYSTEMS in 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. 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 and operate vehicle within the Conditions For Running DTC. You may also operate vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition cycle? If yes, go to step  2. If no, go to next step.
  8. Observe the Capture Info with a scan tool. Are there any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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