If the throttle drives the motor but pedal assist does nothing, the motor and battery are working, and the fault is most likely in the pedal-assist (PAS) input: the settings, a brake cutoff, the cadence sensor and its magnet, or the wiring between them. One source describes the pattern this way: “A working throttle with dead pedal assist usually narrows the problem toward the PAS input path”. It does not prove the rest of the controller is healthy, so work through the checks below in order, cheapest first.
Why the throttle can work when PAS does not
A throttle is a direct request for power. Pedal assist has to be triggered: on a cadence-based system, magnets pass a fixed sensor as the cranks turn, and the sensor sends a signal to the motor controller that tells it you are pedaling. No signal means no assist, however healthy the motor is. Torque-sensing systems work differently; see torque sensors vs cadence sensors, and for the basic difference between the two controls, throttle vs pedal assist.
Checks, in order
Turn the bike off and unplug the battery before touching any wiring or sensor. Check your manual first, because sensor type and procedures differ by system.
1. Settings and display
Make sure pedal assist is enabled and the assist level is above zero. Also look for a walk or service mode, and write down any error code exactly as shown; the code is the fastest route to the cause. See understanding your e-bike display for what the readings mean.
2. Brake cutoff
Many e-bikes have brake cutout switches that cut motor power when you pull a brake lever. A sticky switch or a lever that does not fully release can make the system think the brakes are always on, which can kill assist. Squeeze and release both levers a few times and test again. Do not bypass the cutoff as a repair; it is a safety feature.
3. Magnet and sensor alignment
Look at the magnet ring or disc and the pickup beside it. Check that the ring is seated and turns with the cranks, that no magnets are missing, and that dirt is wiped away. A typical sensor-to-magnet gap is around 1 to 3 mm, but the exact figure depends on the system, so follow your manufacturer’s alignment marks or spacing rather than a generic number. A knock or crash that nudges the sensor out of position is a classic cause of assist that cuts out or never starts.
4. Wiring and connectors
With everything powered down, inspect the sensor cable and plug for bent pins, corrosion, moisture or debris inside the connector. Gently clean a dirty connector and re-seat it firmly. Look for chafed or pinched cable near the crank, where it flexes most. Do not probe powered connectors or splice wires without verified wiring information.
5. The sensor itself
If alignment and wiring are fine and assist is still dead, the sensor may have failed. On some models replacement is a simple unplug-and-swap job. Use the part specified for your system, since sensors differ between brands. If your bike uses a torque sensor or an integrated drive, follow the manufacturer service information or see a shop.
When to stop and see a technician
- Assist engages unpredictably or surges.
- Wiring is damaged, melted or wet inside the connector.
- The same error code returns after restarting.
- Alignment, connectors and settings all check out but assist is still absent. At that point the controller’s input may be at fault; a qualified e-bike technician can test the PAS and controller input.
Sources
- Upway: How to Fix an E-Bike Pedal Assist Sensor
- EM3ev: eBike PAS Sensor Not Working? Causes & Safe Fixes
Last reviewed: October 2026.