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Pedal assist not working? Check the sensors that tell the motor you're pedalling
Pedal assist depends on the bike knowing two things: that you are pedalling and that the wheel is turning. When either signal is missing, the motor sits silent while the display looks perfectly normal.
Quick checks, in order
- Confirm the assist level is not at 0 or Off. Cycle up through the levels and try each.
- Restart the bike with your feet off the pedals and no weight on the cranks. Torque-sensing systems calibrate at power-on; a foot on the pedal throws the zero.
- Spin the rear wheel with the bike lifted and check the display shows speed. No speed reading is a speed sensor problem and stops assist on nearly every system.
- Look at the crank on cadence-sensor bikes: a magnet ring sits behind the chainring and a small sensor next to it. Check the ring is not cracked and the sensor is 1-2 mm away.
- Squeeze and release both brakes and check for a brake icon. A stuck brake sensor mimics a dead pedal sensor exactly.
- If the bike has a throttle, try it. Throttle works and pedal assist does not means the motor is fine and the pedal sensor is the fault.
- Try walk assist. If the wheel drives, the motor and controller are fine.
Likely causes
Speed sensor not reading
How to tell: Speed shows 0 while riding. The spoke or disc magnet has moved, or the sensor is loose or full of mud.
Fix: Align the magnet with the mark on the sensor, 5-10 mm gap, and tighten. Clean the sensor face. Check the plug where the sensor cable meets the main harness.
How to tell: Speed shows 0 while riding. The spoke or disc magnet has moved, or the sensor is loose or full of mud.
Fix: Align the magnet with the mark on the sensor, 5-10 mm gap, and tighten. Clean the sensor face. Check the plug where the sensor cable meets the main harness.
Cadence sensor damaged or misaligned (hub-drive and basic mid-drive bikes)
How to tell: Throttle works, pedal assist does not. The sensor was disturbed by a crank or bottom bracket job, or the magnet ring is broken.
Fix: Reposition the sensor 1-2 mm from the ring. Replace a cracked ring. On BBS mid-drives the sensor is internal and this is a dealer job.
How to tell: Throttle works, pedal assist does not. The sensor was disturbed by a crank or bottom bracket job, or the magnet ring is broken.
Fix: Reposition the sensor 1-2 mm from the ring. Replace a cracked ring. On BBS mid-drives the sensor is internal and this is a dealer job.
Torque sensor failed to zero or has failed
How to tell: Assist is either absent or comes in hard and late. Shimano shows W013, Bafang 25. Happens after a power-on with a foot on the pedal or after a crash.
Fix: Power off, take feet off, power on. If the sensor is dead the drive unit or bottom bracket sensor gets replaced by the dealer.
How to tell: Assist is either absent or comes in hard and late. Shimano shows W013, Bafang 25. Happens after a power-on with a foot on the pedal or after a crash.
Fix: Power off, take feet off, power on. If the sensor is dead the drive unit or bottom bracket sensor gets replaced by the dealer.
Brake sensor stuck on
How to tell: Brake icon lit or assist returns when you unplug a brake sensor connector.
Fix: Adjust or replace the sensor; see the brake sensor guide.
How to tell: Brake icon lit or assist returns when you unplug a brake sensor connector.
Fix: Adjust or replace the sensor; see the brake sensor guide.
Assist profile set to zero in the app or dealer tool
How to tell: Bosch Flow, Shimano E-Tube Ride, or Bafang display settings show the mode's assist at minimum. Second-hand bikes often come with odd profiles.
Fix: Reset the assist levels to default in the app or the display's settings menu.
How to tell: Bosch Flow, Shimano E-Tube Ride, or Bafang display settings show the mode's assist at minimum. Second-hand bikes often come with odd profiles.
Fix: Reset the assist levels to default in the app or the display's settings menu.
Pedal sensor cable broken
How to tell: Cable routed past the crank shows chafing, or the plug near the bottom bracket is full of water.
Fix: Replace the sensor and its cable. Route it clear of the crank arm.
How to tell: Cable routed past the crank shows chafing, or the plug near the bottom bracket is full of water.
Fix: Replace the sensor and its cable. Route it clear of the crank arm.
By drive system
- Bosch: Bosch drive units use an internal torque sensor and an external speed sensor. Speed first: code 503 or 0 km/h on the display means no assist. If the speed reads fine, restart with feet off the pedals. A torque sensor fault inside the unit needs the dealer's DiagnosticTool and usually a drive unit exchange.
- Shimano STEPS: W011 = no speed, W013 = torque sensor initialisation. Both are fixed by adjusting the speed sensor or restarting with no load. Shimano assist strength can be set per mode in the E-Tube Ride app; check the profile is not set to the weakest values.
- Bafang: BBS01/02/HD use an internal torque or cadence sensor and an external speed sensor on the chainstay; code 21 for speed, 25 for torque. The M-series and Ultra use a torque sensor; restart with no load. If you have a throttle and it works, the sensor side is at fault.
- Yamaha PW: Yamaha PW systems calibrate the torque sensor at power-on; hold the bike upright with no load on the pedals and switch on. Error 11 for speed, 13 for torque. A Yamaha that gives assist only in the top gear or only at low cadence usually has a stale wheel-size or speed sensor setting.
- Generic: Cadence-based systems fail at the magnet ring or the sensor 90 percent of the time; both are cheap parts. Check the 3-pin sensor plug for water. Torque-sensing bottom brackets (Sempu, NCTE) on generic bikes need a restart with no load; if they still give nothing, they are replaced as a unit.
When to stop: Go to a shop when the speed sensor, brake sensors, and a clean restart all check out and a mid-drive still gives nothing; that means an internal sensor, and the drive unit is not a home repair.
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
Assist starts a full pedal stroke late. Is that a fault?
On cadence sensors, a little delay is normal; a magnet ring with a missing magnet makes it worse. On torque sensors it should be instant; a delay means the sensor is not zeroed or is failing.
Assist comes in at full power for a second then stops.
That is usually the speed sensor: the motor starts, then the system sees no wheel speed and cuts. Check the magnet gap.
Does pedal assist need me to pedal hard?
On torque sensors, yes, the motor multiplies your effort. Spinning with no load gives little or nothing. On cadence sensors the motor kicks in as long as the cranks turn.