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Home >> Chevrolet >> 2001 >> Venture Base, Van Passenger >> Repair and Diagnosis >> External Pages >> Different car >> Section 26 (Engine Controls Self-Diagnostics - 5.0L & 5.7L) >> Diagnostic Tests >> DTC P0171 & P0174: Fuel Trim System Lean - Bank 1 Or 2 >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2001 GMC Savana, 2001 Chevrolet RV Cutaway, 2001 Chevrolet Cutaway, and 2001 Chevrolet Chevy Express. However, it is still accessible from the selected car via links, so may be relevant.
  1. Perform powertrain diagnostic system check. See POWERTRAIN DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing powertrain diagnostic system check, go to next step.
    2. NOTE: If any DTCs are set, other than P0171 or P0174, repair those first. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  2. Install scan tool. Start and idle engine at normal operating temperature in closed loop. Record long term fuel trim. Turn engine off. Turn ignition on, engine off. Review FREEZE FRAME/FAILURE RECORDS and record displayed data for this DTC. If scan tool indicates long term fuel trim is more than 23 percent, go to next step. If scan tool does not indicate long term fuel trim is more than 23 percent, see DIAGNOSTIC AIDS .
  3. Operate engine at idle. Using scan tool, observe HO2S parameters. If scan tool indicates parameter is within 200-800 millivolts and fluctuating, go to next step. If scan tool does not indicate parameter is within 200-800 millivolts and fluctuating, go to step  5.
  4. Turn engine off. Visually and physically inspect the following items:
    • Vacuum hoses for splits, kinks, and proper connections.
    • Ensure vehicle has sufficient fuel in tank. If fuel pressure is too low this DTC may set.
    • Fuel contamination.

    If problem was found, repair as necessary. After repairs, go to step  7. If problem was not found, go to step  6.

  5. Turn engine off. Inspect for the following:
    • Check HO2S for proper installation.
    • Check to ensure electrical connectors and wires are secure and not contacting exhaust system.
    • Check for a short between Tan wire or Tan/White wire and Purple wire or Purple/White wire for suspect HO2S.

    If problem was found, repair as necessary. After repairs, go to step  7. If problem was not found, diagnose fuel system. See appropriate SYSTEM & COMPONENT TESTING article.

  6. Operate engine at idle. Inspect for the following:
    • Check for missing, loose, or leaking exhaust components, forward of HO2S.
    • Check for vacuum leaks at intake manifold, throttle body and injector "O" rings.
    • Check air induction system and air intake ducts for leaks.
    • Check Secondary Air Injection (AIR) system for leaks, improper air delivery, shut-off valve not closing.
    • Check crankcase ventilation system for leaks.

    If problem was found, repair as necessary. After repairs, go to next step. If problem was not found, diagnose engine mechanical problem.

    7. NOTE: After repairs, use scan tool FUEL TRIM RESET function to reset long term fuel trim.
  7. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate vehicle within code enable criteria. If DTC runs and passes, go to next step. If DTC does not run and pass, go to step  2.
  8. Using scan tool, observe stored information. If scan tool displays any DTCs that have not been diagnosed, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If scan tool does not display any DTCs, system is okay.
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