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Home >> Chevrolet >> 2002 >> Blazer 4D Utility, 4WD, Part Time >> Repair and Diagnosis >> External Pages >> Different car >> Section 547 (Charging System) >> Diagnostic Tests >> DTC P0621: High Generator Turn On Signal >> Diagnostic Procedure

Diagnostic Procedure

WARNING: This page is about a different car, the 2002 GMC Sierra, 2002 GMC Cab & Chassis Sierra, 2002 Chevrolet Silverado, and 2002 Chevrolet Cab & Chassis Silverado. However, it is still accessible from the selected car via links, so may be relevant.
  1. If engine electrical diagnostic system check was performed, go to next step. If engine electrical diagnostic system check was not performed, go to ENGINE ELECTRICAL DIAGNOSTIC SYSTEM CHECK  under ON-VEHICLE TESTING.
  2. Connect scan tool to Data Link Connector (DLC). See COMPONENT LOCATIONS  . Start engine. Using scan tool, observe specific DTC information for DTC P0621 until test runs. If scan tool indicates DTC P0621 failed this ignition, go to next step. If scan tool indicates DTC P0621 passed this ignition, problem may be intermittent. Check wiring and connections, see PRELIMINARY INSPECTION  under TROUBLE SHOOTING.
  3. Test generator turn-on signal circuit, generator harness connector terminal "B" (Red wire) for a short or an open. If no problem exists, go to next step. If problem exists, repair circuit as necessary and go to step  6 .
  4. Inspect ECM harness connector for poor connections. If no problem exists, go to next step. If problem exists, repair circuit as necessary and go to step  6 .
  5. Replace ECM. After replacement, reprogram ECM. See appropriate REMOVAL & INSTALLATION article in ENGINE PERFORMANCE. After repair are made, go to next step.
  6. Review and record scan tool fail records data. Using scan tool, clear DTC's. Start engine. Using scan tool, observe specific DTC Information for DTC P0621 until test runs. If scan tool indicates DTC P0621 passed this ignition, system is okay. If scan tool indicates DTC P0621 failed this ignition, go to step  2 .
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