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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 89 (Engine Control System Self-Diagnostics - 3.1L Engine) >> Diagnostic Tests >> DTC P0172: Rich Fuel Trim System (Bank 1) >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 Pontiac Grand Prix, 2002 Chevrolet Malibu, and 2002 Buick Century. 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.
    NOTE: If any DTCs are set, other than DTC P0172, refer to those DTCs before continuing. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  2. Install a scan tool. Start and idle the engine at the normal operating temperature in Closed Loop. Record the long term fuel trim data. Turn off the engine. Turn ignition on, with 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 HO2S parameters with a scan tool. Does the scan tool indicate that the values are within 200-800 millivolts and fluctuating? If yes, go to next step. If no, go to step  5.
  4. Turn off the engine. Check MAF sensor inlet screen for blockage, vacuum hoses for splits, kinks, and proper connections. Check air intake duct for being collapsed or restricted. Check air filter for being dirty or restricted. Check 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 HO2S for proper installation. Ensure that the electrical connectors and the 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.
  6. Check for excessive fuel in crankcase. Check the evaporative emissions control system. Check fuel pressure regulator for proper operation. Ensure that all injectors are functioning properly. Perform Fuel Injector Balance Test. See appropriate BASIC DIAGNOSTIC PROCEDURES article. Did you find and correct the condition? If yes, go to next step. If no, diagnose engine mechanical problem.
    NOTE: After any of the above repairs, use the scan tool Fuel Trim Reset function in order to reset the Long Term Fuel Trim.
  7. Use the scan tool in order to clear the DTCs. Turn ignition off for 30 seconds. Start engine. Operate the vehicle within the Conditions for Running the DTC. See CONDITIONS FOR RUNNING DTC . Does the DTC run and pass? If yes, go to next step. If no, go to step  2.
  8. Using scan tool, observe the stored information and Capture Info. If scan tool displays any undiagnosed DTCs, diagnose affected DTCs. See DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no DTCs are displayed, system is okay.
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