Bosch error 0x504001: Speed signal tampering detected, reduced assist
The drive unit has flagged the speed signal as manipulated, meaning the system believes the bike is reporting an incorrect speed. Motor support is throttled down and walk assist is usually disabled until the condition is resolved. On most Bosch generations the bike still powers up but climbs and acceleration feel weak.
| Drive system | Bosch eBike (DiagnosticTool / eBike Flow hex code) |
| Severity | Dealer needed |
| Keep riding? | Do not keep riding |
| Typical cost | A replacement spoke magnet is about 5 to 15 EUR, a Bosch speed sensor assembly fitted runs roughly 40 to 90 EUR, and dealer diagnostic time typically adds 30 to 60 EUR. |
Likely causes
- Spoke magnet missing, fallen off, or rotated away from the speed sensor
- Aftermarket tuning chip or dongle fitted to the motor or sensor cable
- Wheel circumference value changed in the eBike Flow app or display to simulate higher speed
- Speed sensor cable damaged, pinched, or connector not fully seated
- Magnet fitted on the wrong side of the spoke or too far from the sensor
- Bent or replaced rear wheel hub where the magnet no longer passes the sensor cleanly
How to fix Bosch error 0x504001
- Power the system off, remove the battery for 30 seconds, refit and switch on to clear the code
- Visually inspect the rear wheel spoke magnet and confirm it sits 5 to 15 mm from the speed sensor on the chainstay
- Realign or refit the magnet if it has shifted, or fit a new Bosch replacement magnet if it is damaged
- Check the eBike Flow app or display for any non-standard wheel circumference or tuning profile and restore factory values
- Remove any aftermarket dongle, chip or wiring tap fitted between the speed sensor and the motor
- Inspect the speed sensor cable and plug for damage or moisture, reseat the connector firmly
- Book the bike with an authorised Bosch dealer if the code returns after these checks for a full DiagnosticTool readout
Warranty: Tampering and tuning-related faults are excluded from warranty, but a genuine speed sensor or wiring failure inside the two-year Bosch warranty window is normally covered for parts and labour.
Typical cost: A replacement spoke magnet is about 5 to 15 EUR, a Bosch speed sensor assembly fitted runs roughly 40 to 90 EUR, and dealer diagnostic time typically adds 30 to 60 EUR.
Frequently asked
Can I reset bosch error 0x504001?
Power cycling the system clears the warning temporarily, but if the tampering condition is still present the code returns within a few seconds of riding. The fault only stays cleared once the underlying cause is corrected.
Is it safe to keep riding with error 0x504001?
No. Motor support is limited, which makes hill starts and traffic manoeuvres unpredictable, and Bosch logs the event so repeated occurrences can trigger further restrictions at service.
How much does the repair cost and is it covered by warranty?
A simple magnet refit is essentially free, while a speed sensor replacement at a dealer typically runs 60 to 150 EUR including labour. Warranty does not cover tuning or modifications, but a genuine sensor failure inside two years is usually covered.
Related Bosch codes
Manuals and video
- Bosch eBike Help Center: official error-code index
- Bosch eBike downloads: quick start guides and battery guide
- Bosch eBike dealer search (DiagnosticTool readout)
Official source: www.ridewill.com
Not an official Bosch document. Compiled from workshop experience and public service information; details can differ per system version and bike brand.