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Home >> Buick >> 1996 >> Roadmaster Base >> Repair and Diagnosis >> Engine Performance >> System >> Engine Control Systems - Tests W/Codes >> Diagnostic Trouble Codes >> DTC P0171 - Fuel Trim System Lean Bank 1 >> Diagnostic Procedures

Diagnostic Procedures

  1. Perform On-Board Diagnostic (OBD) System Check. After performing OBD system check, go to next step.
    NOTE: If other DTC(s) are present, except P0174, diagnose affected DTC(s) first.
  2. Start and warm engine to normal operating temperature. Ensure system is in "closed loop". Using scan tool, select FUEL TRIM DATA LIST and monitor LT FT AVG. BN 1 and ST FT AVG. BN 1 values. If LT FT AVG. is less than 22 percent and ST FT AVG. reads less than 10 percent, go to next step. If not, go to step 4).
  3. Turn ignition on, with engine off. Using scan tool, review FREEZE FRAME and/or FAILURE RECORDS data and note parameters. Turn ignition off for about 15 seconds. Start engine and operate vehicle within the conditions required for this diagnostic to run, and as close to conditions recorded in FREEZE FRAME/FAILURE RECORDS as possible. Select DTC function then enter DTC P0171. If scan tool indicates that this test failed this ignition, go to next step. If scan tool does not indicate that this test failed this ignition, see DIAGNOSTIC AIDS.
  4. If DTC P0174 is also present, go to next step. If DTC P0174 is not present, go to step 6).
  5. Check vacuum hoses for splits, kinks and proper routing. The MAF sensor, air induction system, throttle body, intake manifold, PCV system and EGR valve for vacuum leaks. Check for fuel contamination. Check for good PCM and sensor grounds. Check engine mechanical condition. Repair as necessary. After repairs, go to step 7). If engine mechanical repairs were not necessary, diagnose fuel system. See SYSTEM/COMPONENT TESTS article.
  6. Check bank 1 for exhaust leaks or loose exhaust hardware. Ensure oxygen sensor is properly installed. Check vacuum leaks that will affect bank 1 only. Check engine mechanical condition. After repairs, go to next step. If repairs were not necessary, diagnose fuel system. See SYSTEM/COMPONENT TESTS article.
  7. Repair or replace any faulty items. After repairs, go to next step.
  8. Using scan tool, select DTC, CLEAR INFO function. Start and warm engine to normal operating temperature. Select DTC, SPECIFIC, then enter the DTC P0171. Operate vehicle within the conditions that set the DTC. If scan tool indicates that this test ran and passed, go to next step. If scan tool does not indicate that this test ran and passed, repeat step 2).
  9. Using scan tool, select CAPTURE INFO, REVIEW INFO function. If any undiagnosed DTC(s) are displayed, diagnose affected DTC(s).
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