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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 84 (Engine Control System Self-Diagnostics - 3.1L Engine) >> Diagnostic Tests >> DTC P0171: Lean Fuel Trim System (Bank 1) >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Pontiac Grand Prix, 2002 Chevrolet Malibu, and 2002 Buick Century. 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.
    NOTE: If any DTCs are set, other than DTC P0171, 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 off the engine. Turn ignition on, with engine off. Review the Freeze Frame Records/Failure Records and record displayed data for this DTC. 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. Operate engine at idle. Observe the HO2S parameters with a scan tool. 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 off the engine. 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 off the engine. Inspect the 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 the 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. Inspect for missing, loose, or leaking exhaust components. Inspect for vacuum leaks at the intake manifold and injector O-rings. Inspect the air induction system and air intake ducts for vacuum leaks. Inspect the crankcase ventilation system for leaks. Did you find and correct the condition? If yes, go to next step. If no, diagnose engine mechanical problem.
    NOTE: After any of the above repairs, use the 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. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are displayed, system is okay.
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