1998 Oldsmobile Cutlass BaseFACTORY OEM SERVICE PROCEDURE

DTC B2575: ALC Headlight System Fault: Testing

  1. If BFC diagnostic system check was performed, go to next step. If BFC diagnostic system check was not performed, see procedures in BFC DIAGNOSTIC SYSTEM CHECK  .
  2. If no other ALC DTCs exist, go to next step. If any other ALC DTCs exist, repair those DTCs first.
  3. Turn low beam headlights on. If both low beam headlights illuminate, go to next step. If both low beam headlights do not illuminate, go to step 7).
  4. Using scan tool, read BFC INPUT for LOW BEAM/DRL FEEDBACK. If scan tool displays DRL ON, go to next step. If scan tool does not display DRL ON, go to step 7).
  5. Turn high beam headlights on. If both high beam headlights illuminate, go to next step. If both high beam headlights do not illuminate, go to step 7).
  6. Using scan tool, read BFC INPUT for HIGH BEAM FEEDBACK. If scan tool displays HIGH BEAMS ON, go to step 10). If scan tool does not display HIGH BEAMS ON, go to next step.
  7. Locate problem in headlight and DRL system. See WIRING DIAGRAMS  . Repair as necessary. If repair is complete, go to step 11). If repair is not complete, go to next step.
  8. Remove DRL relay from underhood wiring harness junction block. Replace DRL relay with a known-good relay. Using scan tool, enable DRL relay. If automatic lighting control operates properly, go to step 11). If automatic light control does not operate properly, go to next step.
  9. Remove ALC headlight relay from underhood wiring harness junction block. Replace ALC headlight relay with a known-good relay. Using scan tool, enable ALC headlight relay. If automatic lighting control operates properly, go to step 11). If automatic light control does not operate properly, go to next step.
  10. Replace BFC. See REMOVAL & INSTALLATION  . Go to next step.
  11. Clear DTCs. Perform BFC DIAGNOSTIC SYSTEM CHECK  .


  1. If BFC diagnostic system check was performed, go to next step. If BFC diagnostic system check was not performed, see procedures in BFC DIAGNOSTIC SYSTEM CHECK  .
  2. If no other ALC DTCs exist, go to next step. If any other ALC DTCs exist, repair those DTCs first.
  3. Turn low beam headlights on. If both low beam headlights illuminate, go to next step. If both low beam headlights do not illuminate, go to step 7).
  4. Using scan tool, read BFC INPUT for LOW BEAM/DRL FEEDBACK. If scan tool displays DRL ON, go to next step. If scan tool does not display DRL ON, go to step 7).
  5. Turn high beam headlights on. If both high beam headlights illuminate, go to next step. If both high beam headlights do not illuminate, go to step 7).
  6. Using scan tool, read BFC INPUT for HIGH BEAM FEEDBACK. If scan tool displays HIGH BEAMS ON, go to step 10). If scan tool does not display HIGH BEAMS ON, go to next step.
  7. Locate problem in headlight and DRL system. See WIRING DIAGRAMS  . Repair as necessary. If repair is complete, go to step 11). If repair is not complete, go to next step.
  8. Remove DRL relay from underhood wiring harness junction block. Replace DRL relay with a known-good relay. Using scan tool, enable DRL relay. If automatic lighting control operates properly, go to step 11). If automatic light control does not operate properly, go to next step.
  9. Remove ALC headlight relay from underhood wiring harness junction block. Replace ALC headlight relay with a known-good relay. Using scan tool, enable ALC headlight relay. If automatic lighting control operates properly, go to step 11). If automatic light control does not operate properly, go to next step.
  10. Replace BFC. See REMOVAL & INSTALLATION  . Go to next step.
  11. Clear DTCs. Perform BFC DIAGNOSTIC SYSTEM CHECK  .
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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.