All codes
Service call
SC821
Self-diagnostic error (extended)
AController / HDD
Level A — stop, SP reset after repair
First check
Subcode + firmware, then controller.
What it means
Extended self-diag failed. Read the subcode in the FSM — it points at a specific ASIC/bus.
Likely causes
- Controller
- Firmware
On-site steps
Parts to have on the truck
- Controller
Related codes
Confirm the subcode and part number in the FSM for this serial. Raicoh is a field companion, not a replacement for the book.