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Diagnostic Procedures

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NOTE: If any DTCs are set, other than P0172, diagnose those DTCs before continuing. See DIAGNOSTIC TROUBLE CODE DEFINITIONS .
  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. Install scan tool. Start and idle engine at normal operating temperature in closed loop. Record LTFT data. Turn engine off. Turn ignition on, engine off. Review FREEZE FRAME/FAILURE RECORDS, and record displayed data for this DTC. Does scan tool indicate LTFT is less than -13 percent? If yes, go to next step. If no, see DIAGNOSTIC AIDS .
  3. Operate engine at idle. Using scan tool, observe HO2S parameters. Does scan tool indicate HO2S is fluctuating to more than 800 millivolts and to less than 200 millivolts? If yes, go to next step. If no, go to step  5.
  4. Turn engine off. Visually and physically inspect inlet screen of MAF sensor for blockage, vacuum hoses for splits, kinks, and proper connections, air intake duct for being collapsed or restricted, air filter for being dirty or restricted and 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 engine off. Check HO2S for proper installation. Check to ensure electrical connectors and wires are secured and not contacting exhaust system. Did you find and correct the condition? If yes, go to step  7. If no, see FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.
  6. Inspect for excessive fuel in crankcase. Inspect EVAP system. Test fuel pressure regulator for proper operation. Check to ensure that all injectors are functioning properly. Perform Fuel Injector Balance Test. See FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article. Did you find and correct the condition? If yes, go to step  7. If no, see FUEL SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article.
    7. NOTE: After repairs, use scan tool FUEL TRIM RESET function to reset LTFT.
  7. Using scan tool, clear DTCs. Turn ignition off for 30 seconds. Start engine. Operate vehicle within Conditions for Running DTC. Does DTC run and pass? If yes, go to next step. If no, go to step  2.
  8. Using scan tool, observe stored information. Does scan tool displays any DTCs that have not been diagnosed? If yes, see DIAGNOSTIC TROUBLE CODE DEFINITIONS . If no, system is okay.
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