Zero error code 21
Board Vpack Error
What it means
Board Vpack Error
BMS board pack voltage measurement error
Error — Issue detected, may affect performance.
What to do
- 1Dealer service required. BMS board may need replacement.
Code 21 on the other dash
The number alone is not enough. A Gen2 dash reads code 21 as Board Vpack Error; a Gen3 dash reads the same number as Brake Bulb Out Fault. And the model name does not settle it: the S, SR, DS and DSR kept their names when they moved from the Sevcon dash to Cypher III in 2024, so it is the year that tells you which table applies.
Which bikes use this table
Sevcon-era dash: S, SR, DS (2014-2023), DSR (2016-2023), FX (2014-2025), FXS (2016-2021), FXE (2022-2025). The SDS and XMX owner manuals print the same 0-63 table.
Related codes
Other Gen2 Battery/BMS codes:
What the log file records for the same subsystem:
Questions
What does error code 21 mean on a Zero Gen2 dash?
Board Vpack Error. BMS board pack voltage measurement error. It is classed as error: issue detected, may affect performance.
What should I do about it?
Dealer service required. BMS board may need replacement.
Does code 21 mean the same thing on a Gen3 Zero?
No. On a Gen3 dash, code 21 is "Brake Bulb Out Fault" — a different fault entirely. The two tables share numbers but not meanings, so read the one that matches your dash, not your model name: the S, SR, DS and DSR kept their names when they moved to Cypher III in 2024.
See when this actually happened on your bike
A dash code tells you the fault; the log tells you the pack temperature, the state of charge and the ten minutes leading up to it.
Sources:
The code and its name are transcribed from Zero's own owner manuals; the severity, category and troubleshooting notes are ours. For official diagnostics, consult an authorized Zero Motorcycles dealer.