Bosch error 821: Implausible front wheel speed signals (ABS)

What it means

The ABS front wheel speed signal looks wrong. Bosch lists the sensor disc being missing, damaged or wrongly fitted, very different front and rear wheel sizes, or extreme riding such as riding on the rear wheel only.

Likely causes

• Sensor disc missing, damaged or fitted wrongly
• Very different front and rear wheel diameters
• Extreme riding, e.g. wheelie

Symptoms

• Code 821 on the display
• ABS warning light on

How to fix it

1. Switch the eBike system off, wait a few seconds, then switch it on again.
2. Do a test ride of at least two minutes. The ABS light must go out.
3. If the ABS light stays on, contact your Bosch eBike dealer.

How urgent is it?

Do not rely on ABS until a Bosch eBike dealer has checked it.

Applies to

• Bosch classic system (Intuvia, Nyon, Kiox, Purion, SmartphoneHub)

More Bosch codes

• 800 Internal ABS fault
• 810 Implausible wheel speed sensor signals (ABS)
• 820 Front wheel speed sensor wire fault (ABS)
• 822 Implausible front wheel speed signals (ABS)
• 823 Implausible front wheel speed signals (ABS)
• 824 Implausible front wheel speed signals (ABS)

All 123 Bosch codes →