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Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 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 those DTCs before continuing. See DIAGNOSTIC TROUBLE CODE DEFINITIONS  .
    CAUTION: Road test a vehicle under safe conditions and while obeying all traffic laws. Do not attempt any maneuvers that could jeopardize vehicle control. Failure to adhere to these precautions could result in serious personal injury and vehicle damage.
  2. Connect the scan tool. Start the engine and drive the vehicle under normal conditions until the engine reaches operating temperature and is in closed loop. 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.
    • 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 O2S 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. 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.
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