Bosch error 603: Internal battery error
The battery management system has reported an internal fault. The battery may switch itself off, refuse to charge, or the bike may cut out under load. A one-off can be cleared by a restart; a repeating 603 needs a dealer read-out.
Likely causes
- BMS fault after a deep discharge or long storage
- Cell imbalance or a weak cell group
- Water or corrosion at the battery contacts
- Very high or low temperature
- Battery dropped or physically damaged
How to fix Bosch error 603
- Switch off, remove the battery, clean the contacts
- Charge fully on the original charger
- Let the battery reach room temperature
- Refit and restart
- If the code returns, a dealer must read the BMS with DiagnosticTool; do not open the battery yourself
Warranty: Bosch batteries carry a 2-year warranty (or 500 full charge cycles, whichever comes first); deep discharge from long storage is often classed as user damage.
Typical cost: A replacement Bosch battery is roughly 500-900 EUR/USD; cell replacement by third parties exists but voids Bosch support.
Frequently asked
Can I reset Bosch error 603 myself?
Only by restarting after a full charge. The BMS itself cannot be reset by the rider.
Can I keep riding with error 603?
Usually, but with reduced or interrupted assistance and the risk of the system shutting down mid-ride. Ride home carefully or on muscle power alone; do not plan long rides until the cause is found.
Is error 603 covered by warranty?
Bosch batteries carry a 2-year warranty (or 500 full charge cycles, whichever comes first); deep discharge from long storage is often classed as user damage.
Related Bosch codes
Not an official Bosch document. Compiled from workshop experience and public service information; details can differ per system version and bike brand.