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E-bike pedal assist not working: how to find the fault

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In short

When an e-bike powers on but gives no assist, the usual causes are an assist level set to zero, a brake lever sensor stuck on, a cadence sensor magnet ring that has moved, or a speed sensor that has lost its magnet. Check those in that order. If the display shows an error code or the bike has a torque sensor, look up the code in the manual and ask a shop to recalibrate it if needed.

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An e-bike that switches on, shows charge and speed but does not help when you pedal is one of the most common faults. Because the display works, the battery and main wiring are probably fine. The problem is usually one of the signals the controller needs before it will send power to the motor: that you are pedalling, that you are not braking and how fast you are going. This guide works through those signals from the simplest check to the ones that need a shop.

How pedal assist decides to work

The controller only powers the motor when three things are true. It sees pedalling from a cadence or torque sensor, it sees no brake signal from the lever sensors, and it sees a speed below the assist limit, which is 15.5 mph on a UK-legal bike. If any signal is missing or wrong, assist stops. Our torque vs cadence sensor guide explains the two sensor types.

Assist also stops at the speed limit by design. If it fades only as you reach about 15.5 mph, that is normal, as set out in the gov.uk rules.

Quick checks in order

  1. 1

    Check the assist level. Many displays have a level 0 or off mode. Press the up button and watch the level change.

  2. 2

    Turn the bike off and on again, with the battery firmly locked in.

  3. 3

    Squeeze and release each brake lever. Watch for a brake symbol on the display. A sticky lever or a dislodged sensor magnet can hold the cut-off on.

  4. 4

    Spin the cranks forwards with the rear wheel lifted. Assist should start within a turn or so on a cadence sensor bike.

  5. 5

    Check the speed reading while riding. If it shows zero, the speed sensor or its magnet is the likely cause.

  6. 6

    Note any error code and look it up in the manual.

Note:Lift the rear wheel only on a stand or with a helper, keep hands and clothing away from the chain and spokes, and test at the lowest assist level first.

Brake sensors

Brake sensors are small switches in or on the brake levers. Some use a magnet glued to the lever. If the magnet falls off, moves, or the lever does not return fully, the controller thinks you are braking and cuts assist. On hydraulic brakes the sensor may be a separate switch on the lever body.

Unplugging the brake sensors to test is sometimes suggested online. Only do this if your manual describes it, never ride with them disconnected, and reconnect them straight after. They are an important safety feature.

Cadence, speed and torque sensors

A cadence magnet ring can slip along the axle or crack. Check it sits close to the sensor, usually a few millimetres, and turns with the cranks. Speed magnets on spokes often slide out of line after cleaning or a puncture repair; move it back until it passes the sensor as the manual shows.

Torque sensors are sealed and calibrated. Faults usually show as error codes and need a shop with the maker's tools. Some systems recalibrate when you switch on without pressure on the pedals, so try that first.

SensorWhere it isSigns of a fault
Cadence sensorMagnet ring behind the chainring, sensor on the frameNo assist, or assist starting late
Speed sensorMagnet on a spoke or disc, sensor on the chainstaySpeed shows zero, assist cuts out
Torque sensorInside the bottom bracket or motorWeak or no assist, error codes
Sensor faults and signs

When to get help

If the sensors, brake levers and connectors all look fine, the controller, motor or wiring may be at fault. That is a job for a shop that services your motor system, especially on mid-drive bikes. Keep the receipt and check the warranty first.

If your bike is old and the fault keeps returning, compare repair costs with a newer model. Our electric hybrid guide and e-bikes under 1000 guide compare current options. For other symptoms, see e-bike motor cutting out and e-bike not working.

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Frequently asked questions

Why does my e-bike display work but the motor will not assist? Most often a brake sensor is stuck on, the assist level is zero or a sensor magnet has moved.

Can a speed sensor stop pedal assist? Yes. Without a speed signal many controllers cut assist or show an error.

Why does assist stop at 15.5 mph? That is the legal assist limit for e-bikes in Great Britain. You can pedal faster without help.

Can I ride without pedal assist? Yes, the bike works as a heavy pedal bike. Use low gears on hills.

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