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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 103 (Engine Controls Self-Diagnostics - 2.2L) >> Diagnostic Tests >> DTC P0171: Fuel Trim System Lean >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Pontiac Sunfire, 2002 Pontiac Grand Am, 2002 Oldsmobile Alero, and 2002 Chevrolet Cavalier. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check - engine controls, go to next step.
    2. NOTE: If any DTCs are set, except P0171, refer to those DTCs before proceeding with this diagnostic. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  2. Install scan tool. Review the Freeze Frame/Failure Records and record the displayed data for this DTC. Select Fuel Trim Data parameter. Start engine and observe the Fuel Trim Index. Does the scan tool indicate that the Fuel Trim Index is more than 29 percent? If yes, go to next step. If no, go to DIAGNOSTIC AIDS .
  3. Operate the engine at idle. Using scan tool, observe the HO2S parameters. Does the scan tool indicate that the values are within 200-800 millivolts and fluctuating? If yes, go to next step. If no, go to step  5.
  4. Turn engine off. Visually and physically inspect vacuum hoses for splits, kinks, and proper connections. If fuel pressure is too low this DTC may set. Check for 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. Check the HO2S for proper installation. Check to ensure electrical connectors and wires are secured and not contacting the exhaust system. Check 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.
  6. Operate the engine at idle and check for missing, loose, or leaking exhaust components. Check for vacuum leaks at 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, check for engine mechanical problem.
    7. NOTE: After repairs, use scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim.
  7. Use the scan tool in order to clear the DTCs. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running the DTC. See 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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