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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 379 (Engine Controls Self-Diagnostics - 3.4L) >> Diagnostic Tests >> DTC P0172: Fuel Trim System Rich >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2003 Pontiac Grand Am, 2003 Oldsmobile Alero, 2003 Chevrolet Monte Carlo, and 2003 Chevrolet Impala. 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.
    2. NOTE: If any DTCs are set, other than P0172, proceed to those DTCs before proceeding with this diagnosis. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  2. Connect scan tool. Start and idle the engine at the normal operating temperature in closed loop. Record the Long Term Fuel Trim data. Turn ignition switch to OFF position. Turn ignition switch to RUN position, engine OFF. Review the Freeze Frame/Failure Records and record the displayed data for this DTC. Does the scan tool indicate that the long term fuel trim is less than -13 percent? If yes, go to next step. If no, go to DIAGNOSTIC AIDS .
  3. Operate the engine at idle. Observe the HO2S parameters using a scan tool. Does the scan tool indicate that the values are 200-800 mV and fluctuating? If yes, go to next step. If no, go to  5.
  4. Turn ignition switch to OFF position. Visually and physically inspect the following conditions:
    • Blockage of the inlet screen of the MAF sensor.
    • Splits or kinks in the vacuum hoses.
    • Improper connections of the vacuum hoses
    • Collapsed or restricted air intake duct.
    • Dirty or restricted air filter.
    • Objects blocking the throttle body

    Did you find and correct the condition? If yes, go to next step. If no, go to step  6.

  5. Turn ignition switch to OFF position. Check the HO2S for proper installation. Ensure that the harness connectors and the wires are secure and not contacting the exhaust system. Did you find and correct the condition? If yes, go to step  7. If no, go to FUEL SYSTEMS in SYSTEM & COMPONENT TESTING - 3.4L ALERO, GRAND AM, IMPALA & MONTE CARLO article.
  6. Inspect for the following conditions:
    • Excessive fuel in the crankcase.
    • Evaporative emissions of the control system.
    • Proper operations of the fuel pressure regulator.
    • Proper operation of the fuel injectors.

    Did you find and correct the condition? If yes, go to next step. If no, diagnose mechanical problem. See appropriate article in ENGINES.

    7. NOTE: After repairs, use the scan tool Fuel Trim Reset function to reset the Long Term Fuel Trim.
  7. Clear the DTCs using a scan tool. Turn ignition switch to OFF position for 30 seconds. Start the engine. Operate the vehicle within the Conditions For Running. See CONDITIONS FOR RUNNING . 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.
  8. Using the scan tool, observe the stored information in 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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