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HOMESERVICE MANUALSBUICK1999REGAL LSREPAIR AND DIAGNOSIS (SINGLE PAGE)ENGINE PERFORMANCESYSTEMENGINE CONTROL SYSTEM - TESTS W/CODES - DTC P0453-P0656DTC P0620DTC P0620: GENERATOR PERFORMANCEDIAGNOSTIC PROCEDURES
1999 Buick Regal LS

Diagnostic Procedures

1999 Buick Regal LSSECTION Diagnostic Procedures
  1. Perform On-Board Diagnostic (OBD) System Check. See ON-BOARD DIAGNOSTIC (OBD) SYSTEM CHECK . After performing OBD system check, go to next step.
  2. Start and operate engine at idle. Using scan tool, monitor generator. If scan tool indicates that generator is on, go to step  4. If scan tool does not indicate that generator is on, go to next step.
  3. Turn ignition off. Disconnect generator harness connector. Connect a DVOM between generator "L" terminal and a known-good ground. Start engine. Using scan tool, command generator on. Monitor voltage reading on DVOM. If voltage reading changes from zero to 5 volts, diagnose charging system. See appropriate STARTING & CHARGING SYSTEMS article. If voltage reading does not change from zero to 5 volts, go to next step.
  4. Check generator "L" circuit for open or short to ground. Repair as necessary. After repairs, go to step  8. If circuit is okay, go to next step.
  5. Check generator "L" circuit for short to voltage. Repair as necessary. After repairs, go to step  8. If circuit is okay, go to next step.
  6. Check for poor connection at PCM. Repair as necessary. After repairs, go to step  8. If connections are okay, go to next step.
  7. Replace PCM. program replacement PCM using required equipment. After replacing PCM, go to next step.
  8. Using scan tool, review and record scan tool FAIL RECORDS data. Clear DTCs. Operate vehicle within conditions for setting this DTC. Recheck DTCs. If this DTC resets, go to step  2. If this DTC does not reset, system is okay.
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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.