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Home >> Pontiac >> 2003 >> Vibe Base, AWD >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - Self-Diagnostics >> Diagnostic Tests >> DTC P0171: Fuel Trim System Lean >> Diagnostic Procedures

Diagnostic Procedures

  1. Did you perform the Diagnostic System Check - Engine Controls? If yes, go to next step. If no, perform diagnostic system check - engine controls. See DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
  2. Start engine. Operate vehicle until loop status indicates closed loop. Observe Short Term FT parameter display on scan tool. Is Short Term FT parameter displayed on scan tool less than 20 percent? If yes, see DIAGNOSTIC AIDS . If no, go to next step.
  3. Visually and physically check for any of the following conditions:
    • Splits, kinks, and improper connections in vacuum hoses.
    • Correct installation of PCV valve.
    • Leaks in exhaust system.
    Did any of the above inspections isolate a condition requiring a repair? If yes, go to step  10. If no, go to next step.
  4. Start engine. Run engine until engine reaches normal operating temperature. Observe operation of the following sensors at idle, with a scan tool:
    • Mass Air Flow (MAF) sensor.
    • Engine Coolant Temperature (ECT) sensor.
    • Throttle Position (TP) sensor.
    Compare observed sensor readings with Typical Scan Tool Data Values, located in engine scan tool data list. See SCAN TOOL DATA LIST  under SELF-DIAGNOSTIC SYSTEM. Check vehicle for cause of any errant sensor readings and repair as necessary. Was a repair necessary? If yes, go to step  10. If no, go to next step.
  5. Turn ignition switch to OFF position. Install a fuel pressure gauge. See FUEL GAUGE under FUEL SYSTEMS in REMOVAL & INSTALLATION - 1.8L VIBE article. Observe fuel pressure with engine running at normal operating temperature. Is fuel pressure 44-50 psi (301-347 kPa)? If yes, go to next step. If no, diagnose fuel system. See FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 1.8L VIBE article.
  6. Check fuel for excessive water, alcohol, or other contaminants. See ALCOHOL/CONTAMINANTS-IN-FUEL DIAGNOSIS in SYSTEM & COMPONENT TESTING - 1.8L VIBE article. Was the fuel contaminated? If yes, go to next step. If no, go to step  8.
  7. Replace contaminated fuel. After replacement, go to step  10.
  8. Perform Fuel Injector Balance Test. See FUEL INJECTOR BALANCE TEST WITH SPECIAL TOOL in FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 1.8L VIBE article. Repair or replace as necessary. Was a repair necessary? If yes, go to step  10. If no, go to next step.
  9. Is a lean condition still present? See SYMPTOM DIAGNOSIS in TROUBLE SHOOTING - NO CODES - 1.8L VIBE article. If no, go to step  10.
  10. Use scan tool to clear DTCs. Turn ignition switch to OFF position for 30 seconds. Start engine. Operate vehicle within CONDITIONS FOR RUNNING DTC . Does DTC run and pass? If yes, go to next step. If no, go to step  2.
  11. Using scan tool, observe stored information, CAPTURE INFO. Does scan tool display any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are displayed, system is okay at this time.
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