Brose error 81: Speed sensor signal not recognized
The motor controller is not receiving a valid speed signal from the rear wheel speed sensor. As a result the drive shuts off motor assist because it cannot confirm how fast the bike is moving. Walk assist is also disabled and the display usually shows 0 km/h or freezes the speed reading until the signal returns.
| Drive system | Brose Drive (S, T, C - also used by Bulls, Rotwild, Fantic, BH, Trek Allant) |
| Severity | Fix at home |
| Keep riding? | Ride with caution |
| Typical cost | A replacement spoke magnet costs about 3 to 10 EUR, a complete speed sensor roughly 25 to 70 EUR, and dealer labour for diagnostics and fitment usually adds 40 to 90 EUR. |
Likely causes
- Magnet on the rear wheel spoke is missing, loose, or rotated away from the sensor
- Magnet damaged (cracked, demagnetised, or broken in half) so the sensor cannot detect it
- Speed sensor mounting bracket loose or bent so the gap to the magnet is too large
- Sensor connector contaminated with moisture, corrosion, or road grime
- Sensor cable chafed, pinched, or internally broken near the dropout or along the frame
- Speed sensor itself electrically faulty
How to fix Brose error 81
- With the bike powered on, lift the rear wheel and spin it slowly while watching the display: does the speed figure move or stay at 0?
- Locate the magnet on a rear wheel spoke and the sensor on the left dropout or chainstay.
- Check the gap between the magnet and the sensor as the wheel turns; it should sit between roughly 2 mm and 5 mm.
- If the magnet is loose, slide it back to the centre of the sensor zone and re-tighten the spoke grub screw; replace it if cracked or missing.
- Inspect the sensor plug for green corrosion or dampness, disconnect it, and clean with contact spray or isopropyl alcohol before refitting.
- Follow the sensor cable into the frame entry point and look for chafe, kinks, or pulled pins.
- If the error still appears after magnet and connector checks, the sensor is likely faulty and the bike should go to a Brose service dealer for diagnostic and replacement.
Warranty: A genuine sensor or harness fault inside the two-year warranty window is normally covered as a component defect, but a lost or broken magnet, crash damage, and water-ingested connectors are treated as wear or owner damage and are not covered.
Typical cost: A replacement spoke magnet costs about 3 to 10 EUR, a complete speed sensor roughly 25 to 70 EUR, and dealer labour for diagnostics and fitment usually adds 40 to 90 EUR.
Frequently asked
Can I reset Brose error 81?
There is no user reset that clears this code. Switching the system off and back on only re-checks the signal; the error returns until the magnet and sensor are aligned again or the sensor is replaced.
Is it safe to keep riding with Brose error 81?
Yes, you can pedal home under your own power because the bike still rolls normally, but motor assist will drop out intermittently or stay off, so treat any hill or traffic situation as if the motor is not there.
How much does fixing Brose error 81 cost?
If it is just a magnet or alignment the job is under 15 EUR in parts and a few minutes of time; a new sensor fitted by a dealer typically lands between 65 and 160 EUR including labour.
Related Brose codes
Manuals and video
Official source: Brose error code table, Pedego dealer service guide
Not an official Brose document. Compiled from workshop experience and public service information; details can differ per system version and bike brand.