LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Buick >> 2000 >> Regal GS >> Repair and Diagnosis >> Body & Frame >> Body, Cab Control Systems >> Body Control Modules >> Diagnostic Tests >> DTC B1478: Retained Accessory Power Circuit High >> Testing
April 5, 2026: LEMON Manuals is launched! Read the announcement.

DTC B1478: Retained Accessory Power Circuit High: Testing

  1. Perform retained accessory power (RAP) diagnostic system check. See RETAINED ACCESSORY POWER (RAP) DIAGNOSTIC SYSTEM CHECK  under SELF-DIAGNOSTIC SYSTEM. After performing diagnostic system check, go to next step.
  2. Turn ignition off. Connect scan tool to DLC. Turn ignition on, with engine off. While listening to RAP time delay relay, use scan tool to command RAP time delay relay ON and OFF. If audible clicks are heard at relay signifying that it is turning ON and OFF, go to DIAGNOSTIC AIDS  . If audible clicks are not heard at relay signifying that it is turning ON and OFF, go to next step.
  3. Turn ignition off. Disconnect RAP time delay relay. Turn ignition on, with engine off. Using a test light connected to ground, probe RAP time delay relay terminal C2 (Orange wire). See appropriate POWER DISTRIBUTION wiring diagram in WIRING DIAGRAMS. If test light illuminates, go to next step. If test light does not illuminate, go to step  10 .
  4. Connect test light between RAP time delay relay terminals A1 (Black wire) and C2 (Orange wire). Using scan tool, command RAP time delay relay ON and OFF. If test light illuminates each time relay is turned ON and OFF, go to step  8 . If test light does not illuminate each time relay is turned ON and OFF, go to next step.
  5. If test light stays illuminated each time relay is turned ON and OFF in above step, go to step  7 . If test light does not stay illuminated each time relay is turned ON and OFF in above step, go to next step.
  6. Test Black wire between RAP time delay relay terminal A1 and BCM harness connector C3 terminal A10 for short to voltage or an open. See WIRING DIAGRAMS  . After repair, go to step  13 . If fault is not located and condition still exists, go to step  9 .
  7. Test Black wire between RAP time delay relay terminal A1 and BCM harness connector C3 terminal A10 for short to ground. See WIRING DIAGRAMS  . After repair, go to step  13 . If fault is not located and condition still exists, go to step  9 .
  8. Inspect for poor connections at RAP time delay relay. After repair, go to step  13 . If fault is not located and condition still exists, go to step  11 .
  9. Inspect for poor connections at BCM harness connector C3. After repair, go to step  13 . If fault is not located and condition still exists, go to step  12 .
  10. Repair Orange wire between RAP time delay relay terminal C2 and INADV POWER BUS fuse (15-amp) in fuse block. See appropriate POWER DISTRIBUTION wiring diagram in WIRING DIAGRAMS. After repair, go to step  13 .
  11. Replace RAP time delay relay. After repair, go to step  13 .
  12. Replace BCM. See BODY CONTROL MODULE (BCM)  under REMOVAL & INSTALLATION. After replacement, perform set up procedure. See NEW BCM SETUP  under PROGRAMMING. After replacement, go to next step.
  13. Using scan tool, clear BCM DTCs. Operate vehicle within conditions to set DTC. If DTC B1478 resets, return to step  2 . If DTC B1478 does not reset, system is okay.
scientia non olet · About LEMON Manuals