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HOMESERVICE MANUALSBUICK1998RIVIERAREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCETESTING & DIAGNOSISENGINE CONTROLS - TESTS W/CODESDIAGNOSTIC TROUBLE CODESDTC P0172 - FUEL TRIM SYSTEM RICHDIAGNOSTIC PROCEDURES
1998 Buick Riviera

Diagnostic Procedures

1998 Buick RivieraSECTION Diagnostic Procedures
  1. Perform POWERTRAIN ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK . Read and record FREEZE FRAME and/or FAIL RECORDS data for each DTC set. 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 about -10, go to step 5). If values are not as specified, go to next step.
  4. Using scan tool, read and record FAIL RECORDS data. Clear DTCs and operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, read SPECIFIC DTC while operating vehicle. Continue operating vehicle until DTC P0172 test runs. If scan tool displays DTC P0172 FAILED THIS IGN, go to next step. If scan tool does not display DTC P0172 FAILED THIS IGN, go to DIAGNOSTIC AIDS.
  5. Check air filter element condition. Replace air filter element if necessary and 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 and 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 0% at closed throttle to 100% 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 0, go to step 20). If FUEL TRIM values does not decrease to about 0, go to next step.
  15. Perform FUEL SYSTEM PRESSURE TEST under BASIC FUEL SYSTEM CHECKS in BASIC TESTING 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 FUEL EVAPORATION CONTROL under EMISSION SYSTEMS & SUB-SYSTEMS in SYSTEM/COMPONENT TESTS article. Repair as necessary. After repairs, go to step 21). If no problem is found, go to next step.
  17. Perform INJECTOR BALANCE TEST under FUEL SYSTEM in SYSTEM/COMPONENT TESTS 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. If HO2S 1 is contaminated, replace HO2S 1 and 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 replacing sensor, go to step 21).
  20. Replace MAF sensor. After replacing sensor, go to next step.
  21. Using scan tool, read and record FAIL RECORDS DATA, and clear DTCs. Operate vehicle within conditions noted in FAIL RECORDS data. Using scan tool, select SPECIFIC DTC INFO for DTC P0172. If scan tool displays DTC P0172 FAILED THIS IGN, return to step 2). If scan tool does not display DTC P0172 FAILED THIS IGN, repair is complete.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.