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Home >> Buick >> 2000 >> Regal LS >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control System - Self-Diagnostics - 3.8L >> Diagnostic Tests >> DTC P0172: Fuel Trim System Rich - Bank 1 (Except BONNEVILLE, CAMARO, Firebird & Park Avenue) >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) system check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing OBD system check, go to next step.
  2. If any other DTCs are set, diagnose affected DTCs before proceeding. If no other DTCs are set, go to next step.
  3. Operate vehicle in closed loop mode while using scan tool to read LT and ST FUEL TRIM values. If LT FUEL TRIM and ST FUEL TRIM value is more negative than -10, go to step  5. If values are not as specified, go to next step.
  4. Using scan tool, read and record FAILURE RECORDS data. Clear DTCs and operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until this DTC test runs. If scan tool indicates that this DTC FAILED THIS IGN, go to next step. If scan tool does not indicate that this DTC FAILED THIS IGN, see DIAGNOSTIC AIDS .
  5. Check air filter element condition. Replace air filter element if necessary. After repairs, go to step  21. If air filter element is okay, go to next step.
  6. Check air intake duct for being collapsed or restricted. Repair as necessary. After repairs, go to step  21. If no problem is found, go to next step.
  7. Check throttle body inlet screen for blockage or foreign objects which may partially block airflow sample through MAF sensor. Repair as necessary. After repairs, go to step  21. If no problem is found, go to next step.
  8. Start engine. If high or unsteady idle condition exists, go to next step. If Idle is okay, go to step  11.
  9. Using scan tool, read IDLE AIR CONTROL (IAC) value. If value is less than 100 counts, go to step  11. If value is not less than 100 counts, go to next step.
  10. Turn ignition off. Check throttle body bore, throttle plate and IAC passages for coking and foreign objects. Repair as necessary. After repairs, go to step  21. If no problem is found, go to next step.
  11. Check IAC valve for proper operation. Repair as necessary. After repairs, go to step  21. If no problem is found, go to next step.
  12. Disconnect vacuum hose from fuel pressure regulator and check it for presence of fuel. If fuel is present, replace fuel pressure regulator. After repairs, go to step  21. If no fuel is present, go to next step.
  13. Turn ignition on, engine off. Using scan tool, read TP ANGLE while slowly depressing accelerator pedal. If TP ANGLE increases steadily from zero percent at closed throttle to 100 percent at wide open throttle, go to next step. If TP ANGLE does not increase as specified, to step  19.
  14. Disconnect MAF sensor harness connector. Operate vehicle in closed loop mode while monitoring scan tool LT and ST FUEL TRIM. If both fuel trim values decrease to about zero, go to step  20. If fuel trim values do not decrease to about zero, go to next step.
  15. Check fuel pressure. See BASIC FUEL SYSTEM CHECKS in appropriate BASIC DIAGNOSTIC PROCEDURES article. Repair as necessary. After repairs, go to step  21. If no problem is found, go to next step.
  16. Perform EVAP system check. See EMISSION SYSTEMS & SUB-SYSTEMS in appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step  21. If no problem is found, go to next step.
  17. Perform fuel injector balance test. See FUEL SYSTEM in appropriate SYSTEM & COMPONENT TESTING article. Repair as necessary. After repairs, go to step  21. If no problem is found, go to next step.
  18. Remove HO2S 1 and check it for silicone (powdery white deposit) contamination. Replace HO2S 1 if contaminated. After repairs, go to step  21. If HO2S 1 is not contaminated, see DIAGNOSTIC AIDS .
  19. Check and tighten TP sensor mounting screws. If mounting screws are tight, replace TP sensor. After repairs, go to step  21.
  20. Replace MAF sensor. After replacing sensor, go to next step.
  21. Using scan tool, read and record FAILURE RECORDS data, and clear DTCs. Operate vehicle within conditions noted in FAILURE RECORDS data. Using scan tool, select SPECIFIC DTC INFO for this DTC. If scan tool indicates that this DTC FAILED THIS IGN, go to step  2. If scan tool does not indicate that this DTC FAILED THIS IGN, system is okay.
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