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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 51 (Engine Control System - Self-Diagnostics - 4.2L) >> Diagnostic Tests >> DTC P0172: Fuel Trim System Rich >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Oldsmobile Bravada, 2002 GMC Envoy XL, 2002 GMC Envoy, and 2002 Chevrolet TrailBlazer. 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, see DIAGNOSTIC SYSTEM CHECK - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
    2. NOTE: If any DTCs are set, other than P0172, refer to those DTCs before continuing. See DIAGNOSTIC TROUBLE CODE DEFINITIONS  .
  2. Install a scan tool. Review the Freeze Frame/Failure Records and record displayed data for this DTC. Select Fuel Trim Data parameter. Start the engine and observe the Fuel Trim Index. Does the scan tool indicate that the Fuel Trim Index is less than -42%? If yes, go to next step. If no, see DIAGNOSTIC AIDS  .
  3. Operate the engine at idle. Observe O2S parameters with 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 step  5 .
  4. Turn OFF the engine. Inspect the following items:
    • Vacuum hoses for splits, kinks, and proper connections.
    • The air intake duct for being collapsed or restricted.
    • The air filter for being dirty or restricted.
    • For objects blocking throttle body.

    Did you find and correct the condition? If yes, go to step  7 . If no, go to step  6 .

  5. Turn OFF the engine. Inspect the O2S for proper installation. Ensure electrical connectors and wires are secured and not contacting the exhaust system. Did you find and correct the condition? If yes, go to step  7 . If no, diagnose fuel system. See appropriate BASIC DIAGNOSTIC PROCEDURES article.
  6. Inspect for the following conditions:
    • Excessive fuel in the crankcase.
    • The evaporative emissions control system.
    • The fuel pressure regulator for proper operation.
    • Ensure that all injectors are functioning properly.
    • Perform the Fuel Injector Balance Test.

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

    7. NOTE: After any of the above repairs, use scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim.
  7. Clear the DTCs with a scan tool. Turn OFF the ignition for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running DTC. Does the DTC run and pass? If yes, go to next step. If no, go to step  2 .
  8. Observe the stored information, Capture Info with a scan tool. Does the scan tool display any DTCs that you have not diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no, system is okay.
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