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Home › Saturn › 2003 › Ion 1 Standard › Repair and Diagnosis › Engine Performance › System › Engine Controls - Self-Diagnostics › Diagnostic Tests › DTC P0171: Fuel Trim System Lean › Diagnostic Procedures

Diagnostic Procedures

  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 20 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 mV and fluctuating? If yes, go to next step. If no, go to step  5.
  4. Turn engine off. Visually and physically inspect the following:
    • Vacuum hoses for splits, kinks, and proper connections.
    • Fuel pressure. 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  8. If no, go to step  7.

  5. Turn ignition switch to OFF position. Turn ignition switch to RUN position, engine OFF. Observe the Manifold Absolute Pressure (MAP) sensor pressure parameter using a scan tool. See ALTITUDE VS. BAROMETRIC PRESSURE  table. The MAP sensor pressure should be within the range specified for your altitude. Does the MAP indicate the correct barometric pressure? If yes, go to next step. If no, go to DTC P0106: MANIFOLD ABSOLUTE PRESSURE SYSTEM PERFORMANCE .
  6. Turn ignition switch to OFF position. Inspect for the following conditions:
    • The O2S for proper installation.
    • Ensure harness connectors and wires are secured and not contacting the exhaust system.
    • A short between the signal circuit and low reference circuit.

    Did you find and correct the condition? If yes, go to step  8. If no, diagnose fuel system. See FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 2.2L ION article.

  7. 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. See appropriate article in ENGINES.
    8. NOTE: After repairs, use scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim.
  8. Using the scan tool, clear the DTCs. Turn ignition switch to OFF position for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING DTC . You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. Did the DTC fail this ignition? If yes, go to step  2. If no, go to next step.
  9. Using a scan tool, observe the 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 at this time.
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