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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 102 (Engine Controls - Self-Diagnostics - 3.5L) >> Diagnostic Tests >> DTC P0171: Fuel Trim System Lean >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Oldsmobile Intrigue and 2002 Oldsmobile Aurora. 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, go to DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
    NOTE: If any other DTCs are set, repair DTCs before continuing with this test. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  2. Start engine and allow it to idle. Ensure engine is at normal operating temperature. Using scan tool, record LONG TERM FUEL TRIM data. Turn ignition off. Turn ignition on. Using scan tool, review FREEZE FRAME RECORDS and/or FAILURE RECORDS and record data. If long term fuel trim is more than 23 percent, go to next step. If long term fuel trim is 23 percent or less, see DIAGNOSTIC AIDS .
  3. Start engine and allow it to idle. Using scan tool, observe HO2S voltage. If voltage is 200-800 millivolts and fluctuating, go to next step. If voltage is not 200-800 millivolts or is not fluctuating, go to step  5.
  4. Turn ignition off. Check vacuum hoses for splits, kinks and proper routing. Check for contaminated fuel. Ensure fuel tank has enough fuel. Check fuel pressure. See appropriate BASIC DIAGNOSTIC PROCEDURES article. Fuel pressure that is too low can cause a lean condition. If any problems are found, repair as necessary. After repairs, go to step  7. If no problems are found, go to step  6.
  5. Turn engine off. Inspect 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 low reference circuit. Did you find and correct the condition? If yes, go to step  4 7. If no, diagnose fuel system. See FUEL SYSTEMS in appropriate BASIC DIAGNOSTIC PROCEDURES article.
  6. Operate engine at idle. Check for missing, loose, or leaking exhaust components. Check for vacuum leaks at intake manifold, throttle body and injector "O" rings. Check air induction system and air intake ducts for leaks. Check crankcase ventilation system for leaks. If any problems are found, repair as necessary. After repairs, go to next step. If no problems are found, check engine mechanical condition and repair as necessary.
  7. After repairs, using scan tool fuel trim reset function, reset long term fuel trim. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate vehicle within conditions for running the DTC. See CONDITIONS FOR RUNNING DTC . If DTC runs and passes, go to next step. If DTC resets, go to step  2.
  8. Using scan tool, check for any other DTCs that are set. If no other DTCs are set, system is okay. If any other DTCs are set, repair DTCs as necessary. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
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