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Pedal assist sensor

The pedal assist sensor tells the controller you are pedaling, or how hard. Replacements are system specific, since pedal sensor signals are not standardized.

Last edited Nov 8, 2026 by Pedalwise team Edit History Add a subpage

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The pedal assist sensor, often called the PAS sensor, tells the controller when you pedal so it can add motor power. Grin Technologies describes two kinds: cadence sensors that mount on the crankset and send a signal whenever the pedals turn, and torque sensors that usually replace the bottom bracket and measure how hard you push (Grin, e-bike parts explained).

A pedal sensor is replaced with the part made for your system and plugged in at its connector, or by a pro. A torque sensor built into the bottom bracket is a shop job. Never splice sensor wires, and remove the battery before you unplug anything.

What it's used for

Replace it when assist doesn't come on, comes on late, or cuts in and out while the throttle still works, once settings and plugs check out. Start with No pedal assist and Inspect and clean connectors. On many hub motor bikes the sensor plugs into the controller with the other parts, as in Rad's RadRunner controller guide (Rad RadRunner controller guide).

What to look for

  • Cadence or torque. Replace like with like. A torque sensor is a different part from a cadence ring and magnet.
  • Your exact model. Ride1Up sells a bottom bracket cadence sensor as a Roadster v2 part (Ride1Up Roadster parts).
  • Your system. For Bafang mid-drives, California Ebike sells the PAS circuit and the PAS magnetic disc listed for the BBS02 or BBSHD (California Ebike cables and sensors).
  • Be careful with universal sensors. Area 13 E-Bikes sells a universal pedal assist sensor (Area 13), but Grin warns that pedal sensor signals are not standardized, so compatibility with a controller is hard to predict (Grin). Confirm with the seller that it works with your controller before you buy.
  • Fitting. A cadence sensor sits behind the crank, so fitting one may need a crank puller.

Typical price

  • Area 13 E-Bikes lists its Universal Pedal Assist (PAS) Sensor at $14.99 (read Nov 9, 2026) (Area 13).
  • California Ebike lists the Bafang PAS circuit for BBSHD or BBS02 at $19.95 (read Nov 9, 2026) (California Ebike).
  • California Ebike lists the Bafang PAS magnetic disc from $17.95 (read Nov 9, 2026) (California Ebike).

Where to buy

  1. Your bike maker's parts store or support team, such as Ride1Up.
  2. For Bafang systems, a Bafang service center such as California Ebike.
  3. Independent specialists in Where to buy e-bike repair parts.
  4. A local shop, through find a shop.

Guides that use it

Sources

Stuck after these checks? Find a shop near you.

Guides that use this

Need a pro?

If these steps didn't fix it, find a shop near you in our partner network. For battery or wiring trouble, look for shops marked Battery and electrical.

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