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Home >> GMC >> 2003 >> Safari Van Cargo, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 433 (Engine Controls - Self-Diagnostics - 6.0L Bi-Fuel & CNG) >> Diagnostic Tests >> DTC P0171: Fuel Trim System Lean - Bank 1 & DTC P0174: Fuel Trim System Lean - Bank 2 >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2003 GMC Sierra and 2003 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. Did you perform the Diagnostic System Check - Alternative Fuels - Engine Controls. If yes, go to next step. If no, see DIAGNOSTIC SYSTEM CHECK - ALTERNATIVE FUELS - ENGINE CONTROLS  under SELF-DIAGNOSTIC SYSTEM.
    2. NOTE: If any DTCs other than P0171 or P0174 are set, refer to those DTCs before continuing. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  2. Install the scan tool. Start and idle the engine at the normal operating temperature in Closed Loop. Record the long term fuel trim. Turn the engine off. Turn ignition on, with engine off. Review the Freeze Frame/Failure Records and record the displayed data for this DTC. If the scan tool indicates that the long term fuel trim is greater than 28 percent, go to next step. If scan tool indicates long term fuel trim is less than 28 percent, see DIAGNOSTIC AIDS .
  3. Operate engine at idle. Observe the HO2S parameters using a scan tool. If the scan tool indicates that the HO2S parameter is 200-800 mV and fluctuating, go to next step. If the scan tool indicates that the HO2S parameter is not 200-800 mV and fluctuating, go to step  5.
  4. Turn the engine off. Visually and physically inspect the vacuum hoses for splits, kinks, and proper connections. See VACUUM DIAGRAMS - SIERRA & SILVERADO article. Ensure that the vehicle has sufficient fuel rail pressure. If the fuel rail pressure is too low this DTC may set. See FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 6.0L CHEVY EXPRESS, SAVANA, SIERRA & SILVERADO - BI-FUEL & CNG article. Did you find and correct the condition? If yes, go to step  7. If no, go to step  6.
  5. Turn the engine off. Inspect the HO2S for proper installation. Verify the electrical connectors and the wires are secure and not contacting the exhaust system. Test for continuity between the HO2S signal circuit and the low reference circuit. Did you find and correct the condition? If yes, go to step  7. If no, see FUEL SYSTEM DIAGNOSIS under FUEL SYSTEMS in BASIC DIAGNOSTIC PROCEDURES - 4.8L, 5.3L & 6.0L "C", "G", "H", "K", "N", "S" & "T" SERIES - GASOLINE article.
  6. Operate the engine at idle. Inspect for any missing, loose, or leaking exhaust components forward of the HO2S. Inspect for vacuum leaks at the intake manifold, throttle body, and injector "O" rings. Inspect the air induction system and the air intake ducts for leaks. Inspect the crankcase ventilation system for leaks. Did you find and correct the condition? If yes, go to next step. If no, check engine mechanical condition. See appropriate article in ENGINES.
    7. NOTE: After repairs, use the scan tool FUEL TRIM RESET function in order to reset the Long Term Fuel Trim.
  7. Using a scan tool, clear the DTCs. Turn ignition off for 30 seconds. Start the engine. Operate the vehicle within the Conditions for Running the DTC. You may also operate the vehicle within the conditions that you observed from the Freeze Frame/Failure Records. If the DTC failed this ignition cycle, go to step  2. If the DTC did not fail this ignition cycle, go to next step.
  8. Observe the Capture Info using a scan tool. Are there any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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