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E-bike lights not working? Check the switch, the wiring, and the light itself
Lights powered from the e-bike system fail at the connector far more often than at the bulb, because the wire runs the length of the bike and gets pinched at the fork and the rear rack. Start with the switch on the display, then follow the wire.
Quick checks, in order
- Find the light button: Bosch Purion/Intuvia hold + for a second, Kiox and Smart System press the light button on the remote, Shimano hold the top button, Bafang hold + for 2 seconds, generic displays hold + or a dedicated light button. The display shows a headlamp icon when on.
- Check whether the light is set to automatic. Some systems have an auto-light setting where the light is off in daylight; try in a dark garage.
- Check both lights. If the front works and the rear does not, or vice versa, the fault is in that light's wire or the light, not the system.
- Follow the front light wire from the drive unit or controller up the down tube and along the fork; check for a pinch at the head tube where the bars turn. Follow the rear light wire along the rack stays and under the mudguard.
- Unplug and reseat the small 2-pin connectors at each light and at the drive unit or controller.
- Check the light's mounting bolt. Many rear lights ground through the rack; a loose or painted mounting point breaks the circuit.
- Check for a code: Bosch 502 is a light fault, Shimano W030 is too many lights connected. A code means the system sees a short or an overload on the light circuit.
Likely causes
Light switched off or in auto mode
How to tell: No headlamp icon on the display; the light works in a dark room.
Fix: Turn it on or set to manual in the display or app.
How to tell: No headlamp icon on the display; the light works in a dark room.
Fix: Turn it on or set to manual in the display or app.
Broken or pinched wire
How to tell: Light flickers when the bars turn or the rack is pushed. Wire shows a crush mark at the fork crown or under the rack.
Fix: Repair with a soldered and heat-shrunk joint or replace the cable. Reroute with a little slack at the steering.
How to tell: Light flickers when the bars turn or the rack is pushed. Wire shows a crush mark at the fork crown or under the rack.
Fix: Repair with a soldered and heat-shrunk joint or replace the cable. Reroute with a little slack at the steering.
Corroded connector
How to tell: Green or white deposits on the 2-pin plug, especially at the rear light in a wet climate.
Fix: Clean with contact cleaner, add a smear of dielectric grease, reseat.
How to tell: Green or white deposits on the 2-pin plug, especially at the rear light in a wet climate.
Fix: Clean with contact cleaner, add a smear of dielectric grease, reseat.
Light failed
How to tell: Voltage present at the connector (6 V or 12 V DC depending on system) but no light; or the light has water inside.
Fix: Replace with a light rated for the system's voltage. Bosch is 12 V DC on older units and 6-12 V on Smart System; Shimano is 6 V; Bafang is typically 6 V from the controller.
How to tell: Voltage present at the connector (6 V or 12 V DC depending on system) but no light; or the light has water inside.
Fix: Replace with a light rated for the system's voltage. Bosch is 12 V DC on older units and 6-12 V on Smart System; Shimano is 6 V; Bafang is typically 6 V from the controller.
Light circuit overloaded or shorted
How to tell: Error code on the display (Bosch 502, Shimano W030), lights went out after adding a light or a USB accessory.
Fix: Remove the extra load. Check for a chafed wire shorting to the frame. On Bosch the light circuit is limited to about 17 W in total.
How to tell: Error code on the display (Bosch 502, Shimano W030), lights went out after adding a light or a USB accessory.
Fix: Remove the extra load. Check for a chafed wire shorting to the frame. On Bosch the light circuit is limited to about 17 W in total.
Light not enabled in configuration
How to tell: Lights never worked; bike is second-hand or was built without lights and they were added later.
Fix: The dealer enables the light output in the tool (Bosch, Shimano, Yamaha) or you enable it in the display settings (Bafang, generic).
How to tell: Lights never worked; bike is second-hand or was built without lights and they were added later.
Fix: The dealer enables the light output in the tool (Bosch, Shimano, Yamaha) or you enable it in the display settings (Bafang, generic).
By drive system
- Bosch: Code 502 = light fault (short or overload). The light circuit is 12 V on Active/Performance Gen 2-4 and configurable on Smart System; lights must be Bosch-approved for the dealer to enable them. On Purion hold + to toggle; on Smart System use the light button on the remote or the Flow app. If one light fails and the other works, it is the wiring to that light.
- Shimano STEPS: Lights are 6 V from the drive unit; hold the top button on the switch unit to toggle. W030 means the total light load is above what the unit supplies; remove an accessory. The light connector on the drive unit is a small 2-pin plug under the motor cover that is easy to leave half-inserted after a service.
- Bafang: Hold + for 2 seconds; the display shows a lamp icon and the backlight brightens. The light output is 6 V from the controller and the lights must match. If the icon comes on but no light, check the 2-pin plug on the harness near the display; if the icon never appears, check the light setting in the display menu.
- Yamaha PW: Lights are switched from the display; a lamp icon confirms. Yamaha lights are 6 V and the output is enabled by the dealer. A code 24 on some Yamaha displays indicates a fault on the light or accessory output.
- Generic: KT and similar controllers put out 6 V (sometimes 12 V) on a 2-wire light lead; check the controller label. The light is toggled by holding + on the display. Many generic bikes have a separate battery-powered rear light unrelated to the system; check whether yours is wired at all.
When to stop: Go to a shop if a code stays on after removing accessories and checking for chafed wires, or if the light output needs enabling in the dealer tool; a short on the light circuit can take the drive unit with it if ignored.
Related error codes
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 fit any bike light to the e-bike's light output?
Only one rated for the output voltage and within the power limit. A 12 V light on a 6 V output is dim; a 6 V light on 12 V dies quickly. Bosch additionally requires approved lights for the dealer to enable the output.
The lights dim when I use the motor hard.
Slight dimming under heavy load is normal on some systems. Strong dimming or flicker suggests a poor connection in the light wiring or a light drawing more than the output is rated for.
My rear light works but the front doesn't after a crash.
The wire at the fork crown or head tube almost certainly got pinched or pulled. Turn the bars fully and inspect; the break is usually right there.