When an e-bike display lights up but the motor does nothing, the battery is delivering power to the electronics, so the fault is in what tells the motor to run: an assist setting, a brake cutoff signal, a pedal or speed sensor, a connector, or the drive system itself. Check them in that order, because the first three cost nothing to rule out.
1. Settings and conditions (two minutes)
- Assist level. Make sure assist is switched on and set above the lowest “off” setting, then pedal.
- Pedal input. The motor responds to the sensor type your bike has. A cadence sensor only detects that the cranks are turning, while a torque sensor measures how hard you push; see torque vs cadence sensors. Pedal steadily for several crank revolutions before concluding there is no assist.
- Throttle versus pedal assist. E-bikes broadly divide into pedelecs, which need the rider to pedal, and bikes whose motor is controlled by a throttle. Throttle vs pedal assist explains the difference.
- Speed. In Europe, the standard for electrically power assisted cycles (EN 15194) describes output that is progressively reduced and finally cut off as the bike reaches 25 km/h. If the motor stopped at about that speed on a bike sold in Europe, this may be normal behavior, not a fault. Limits in other markets differ; check your manual.
- Battery state. Charge the battery fully and retest; if it will not charge, see why an e-bike battery will not charge.
2. Brake cutoff sensors
A brake cutoff is a simple switch or magnetic sensor in each brake lever. It tells the controller that a brake is applied so the motor stops at once; that signal takes priority over cadence, torque and throttle inputs. A sensor stuck in the braking state leaves the display on while, as one guide puts it, “the motor will refuse to respond to throttle or pedal assist inputs.”
The cutoff is a safety feature. Forum reports describe it as immediate: “the properly installed brake sensors will cut the motor instantly.” In a separate forum thread about a motor that kept driving the bike, the owner concluded the cause was that “the sensors and/or magnet weren’t sticking to the brake levers correctly.” That is the opposite symptom (a cutoff that did not work), and it shows why the sensor and magnet must sit properly on the lever.
- Switch the system off. Look at each brake lever: the sensor and its magnet (or switch) should sit close together at rest and separate when the lever is pulled. Check that nothing has shifted after a crash, a lever adjustment or a brake service.
- A magnet displaced by only a couple of millimeters can be enough: one rider reported a lit display and a dead motor after the lever magnet shifted about 2 mm, because the controller believed the brake was held.
- Check that each lever returns fully to rest and the cable and sensor wires are not pinched.
- Re-seat the sensor connectors firmly, power on and test again.
Do not ride with a brake cutoff disconnected or bypassed. It removes a stop function, and the brakes themselves still need to work normally. If a sensor, lever or wire looks damaged, or the fault continues, have a bike shop that handles e-bikes diagnose it. Do not probe controller wiring with a multimeter unless you know the pinout; a mistake can damage the controller.
3. Pedal-assist and speed sensors
On many systems the controller needs pulses from a magnet passing a sensor. On a bottom-bracket cadence sensor that is a ring of magnets at the cranks; on many systems a separate magnet on a spoke and a sensor on the frame report wheel speed.
- One owner of a Bafang mid-drive reported that “it was a broken PAS magnet ring that caused the problem.”
- On Bosch systems a speed sensor problem is a known cause of faults. One guide describes error 503 as “a speed sensor malfunction. It is often caused by a shifted spoke magnet or a damaged sensor cable.” That guide also says “Usually, these parts need professional intervention to fix.”
Visible checks are safe: look for a magnet that has slipped on its spoke, a cracked or missing magnet, and a sensor cable that has been pulled or rubbed through. Do not bend or force parts to realign them; if realignment is needed, a dealer can do it to the manufacturer’s gap specification.
4. Error codes
Many systems show a numbered code on the display when they detect a fault; Bosch, for example, lists separate codes for stuck buttons, loose display wiring (414) and temperature faults (540). Codes are brand-specific, so look up the code in your manufacturer’s documentation, not in a general list. For Bosch systems specifically, a Bosch code guide advises: “Try restarting the bike, and if it doesn’t work, take it in for servicing.” See understanding your e-bike display for what the other readings mean.
5. Connectors, motor and controller: stop here
Water or corrosion in a motor or controller connector, a failed motor sensor, or a failed controller all produce the same symptom: a display that works and a motor that does not. Telling them apart needs manufacturer diagnostic tools or electrical test equipment. Do not open the motor, controller or battery, and do not repair battery packs. If a visible connector is wet, corroded or burned, or you smell burning, stop using the bike and have it inspected. Which parts are involved depends on the drive layout; hub and mid-drive motors differ in where the sensors and wiring sit.
Quick reference
| What you see | Most likely area | What to do |
|---|---|---|
| Brake icon shows with levers released | Possible brake cutoff sensor or wiring fault (some displays show a lever icon when that circuit is active) | Check sensor and magnet seating; see a shop if it persists |
| Motor works on throttle but not when pedaling | Possible pedal-assist sensor, magnet or wiring issue | Inspect magnet ring and connector; see a shop |
| Assist stops only at speed | Normal speed limit behavior | None needed |
| Error code on display | Depends on brand | Restart; look up the code; dealer if it returns |
| Nothing found, still no assist | Motor, controller or connectors | Professional diagnosis |
Sources
- Electric Bike Review forum: Ebike Won’t Stop
- Electric Bike Review forum: Bafang BBS02 750w mid drive motor
- EM3EV: Ebike Brake Sensor Guide
- RideReview: Your guide to deciphering these Bosch e-bike error codes
- Wikipedia: Electric bicycle
- iTeh Standards: EN 15194:2017+A1:2023
Last reviewed: October 2026.