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Bosch error 502: Fault in the bike lighting

Bosch BES2 & BES3Fix at homeSafe to keep riding

The drive unit has detected a problem on the lighting circuit it powers: usually a short circuit, a dead lamp or an overload. Assistance is not affected; the lights may not work.

Likely causes

Front or rear light bulb or LED unit failed
Damaged or chafed light cable, often at the fork crown or under the rear rack
Short circuit or water in a light connector
Non-approved light with the wrong voltage or too much power fitted
Light connector at the drive unit loose or corroded

How to fix Bosch error 502

Switch the lights off in the display menu and restart; if the code disappears, the fault is in the lighting circuit
Check both lights for visible damage and water
Follow the light cables and look for cuts, pinches or exposed wire
Unplug the rear light and test with only the front light connected, then the other way round, to find the faulty side
Replace the faulty lamp or cable; make sure any replacement is a Bosch-approved 6 V or 12 V light matching your system
If the code stays with both lights disconnected, the drive unit's light output is damaged: dealer job

Go to a dealer if: A dealer is needed when the code persists with both lights unplugged, or when the wiring runs inside the frame and needs professional replacement.
Warranty: Dirty contacts, damaged cables and water ingress are treated as wear or user damage and are rarely covered; a genuine component fault within the 2-year warranty normally is.
Typical cost: A replacement light is 20-80 EUR/USD, a cable 10-30, plus labour; a damaged light output on the drive unit is a much bigger repair.

Still stuck? Take a photo of the display and show it to a local e-bike workshop. Bring the bike's system name (e.g. Bosch Performance Line CX) and the exact code; that saves diagnostic time and money.

Frequently asked

Can I reset Bosch error 502 myself?

Yes. Fix or disconnect the faulty light and restart the system; the code clears as soon as the lighting circuit is healthy.

Can I keep riding with error 502?

Yes. The drive keeps working normally with this code; it is a warning rather than a safety stop. Get it looked at when convenient, especially if it keeps coming back.

Is error 502 covered by warranty?

Dirty contacts, damaged cables and water ingress are treated as wear or user damage and are rarely covered; a genuine component fault within the 2-year warranty normally is.

Related Bosch codes

550 · Invalid load detected 500 · Internal fault in the drive unit

Not an official Bosch document. Compiled from workshop experience and public service information; details can differ per system version and bike brand.