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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 141 (Engine Controls Self-Diagnostics - 5.7L - Bi-Fuel) >> Diagnostic Tests >> DTC P0172: Fuel Trim System Rich >> Diagnostic Procedures

Diagnostic Procedures

WARNING: This page is about a different car, the 2002 GMC Savana Special, 2002 GMC Savana Camper Special, 2002 GMC Savana, and 2002 Chevrolet Chevy Express. 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. Using scan tool, capture DTC information from AF ECM. Check PCM and AF ECM for additional DTCs. If additional DTCs are set, go to next step. If no additional DTCs are set, go to step  4 .
  3. Diagnose and repair additional DTCs before attempting to diagnose this DTC. See DIAGNOSTIC TROUBLE CODE DEFINITIONS  . After repairs, go to step  14 .
  4. DTC may have been set by one of the following conditions:
    • An HO2S signal wire intermittently shorted to voltage.
    • HO2S connector water intrusion.
    • RTV silicone contaminated HO2S.
    • Rich engine condition such as EVAP canister purge system malfunction, gasoline contaminated engine oil, incorrect CNG fuel pressure, leaking gasoline fuel pressure regulator, an inaccurate MAF sensor or a restricted air filter or intake air duct.

    Repair as necessary. Was a condition found and repaired? If yes, go to step  14 . If no, go to next step.

  5. Reconnect all disconnected or removed components. Using scan tool, clear DTCs from PCM and AF ECM. Communicate with AF ECM and reset fuel trim values. Turn ignition off for 30 seconds. Start engine and view captured data FREEZE FRAME records on scan tool. Operate vehicle within Conditions For Running DTC. Monitor short term fuel trim values. Do the fuel trim values indicate a rich mixture condition is present or does a fuel trim DTC set? If yes, go to step  7 . If no, go to next step.
  6. The fault is not present. See DIAGNOSTIC AIDS  . Are any DTCs stored that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS  . If no, see INTERMITTENT CONDITIONS  under SELF-DIAGNOSTIC SYSTEM.
  7. Perform fuel system diagnosis. See FUEL SYSTEM DIAGNOSIS (BI-FUEL & CNG) under FUEL SYSTEM (BI-FUEL & CNG) in SYSTEM & COMPONENT TESTING - TRUCKS - EXCEPT TRACKER article. Was a CNG fuel system problem found and repaired? If yes, go to step  14 . If no, go to next step.
  8. Inspect the oxygen sensor signal and low circuit for continuity between the AF ECM connector terminals and the oxygen sensor connector terminals. Inspect these circuits for shorts to other circuits or to ground. Ensure the oxygen sensor, PCM and the AF ECM connectors are disconnected before testing circuits. Repair wiring as necessary. Was a wire repair made? If yes, go to step  14 . If no, go to next step.
  9. Reconnect all disconnected or removed components. Using scan tool, clear DTCs from PCM and AF ECM. Communicate with PCM and reset fuel trim values. Turn ignition off. Remove CNG fuse (20-amp) located in underhood fuse block. Removing CNG fuse will force switch to gasoline operation and Fuel Indicator Lamp (FIL) may not illuminate. Start engine and view captured data FREEZE FRAME records on scan tool. Operate vehicle within Conditions For Running DTC. Monitor short term fuel trim values. Do the fuel trim values indicate a rich mixture condition is present or does a fuel trim DTC set? If yes, go to next step. If no, go to step  13 .
  10. Remove HO2S bank 1 sensor 1 and visually inspect for RTV silicone contamination. Is the oxygen sensor contaminated? If yes, go to step  12 . If no, go to next step.
  11. Repair cause of engine running rich condition as outlined in step  4 . After repairs, go to step  14 .
  12. Replace HO2S. Before replacing HO2S, repair source of contamination. See OXYGEN SENSOR under ENGINE SENSORS & SWITCHES in REMOVAL, OVERHAUL & INSTALLATION - CHEVY EXPRESS & SAVANA - GASOLINE. After repairs, go to step  14 .
  13. Replace the fuel mixer. See FUEL MIXER under FUEL SYSTEMS in REMOVAL, OVERHAUL & INSTALLATION - CHEVY EXPRESS & SAVANA - BI-FUEL. When complete, go to next step.
  14. Reconnect all disconnected components and connectors. Using scan tool, clear DTCs for PCM and AF ECM. Start engine and allow to idle until engine reaches normal operating temperature. Select DTC and specific DTC function. Enter DTC number and operate vehicle, within Conditions For Setting DTC, until scan tool indicates diagnostic has run. Does the scan tool indicate the DTC passed? If yes, system is okay. If no, go to step  2 .
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