KT-D12L Left-Side E-Bike Pedal Assist Sensor, 12 Magnet, SM-3Y

The motor stops helping when the pedal sensor stops reporting. This KT-D12L is the left-side version of the KT-D12 assist sensor, with twelve signal outputs and an SM-3Y three-wire plug, and it mounts on the axle without removing the crank. For anyone repairing an e-bike that has gone quiet.

Assist that follows the pedals again

✅ No crank removal The left-side body sits on the axle, so the crank and bottom bracket stay untouched during the swap.

✅ Twelve signals a turn Twelve outputs per pass of the magnet plate give the controller frequent updates, so assist picks up soon after you start pedalling.

✅ A part, not a new bike When the sensor is the fault, swapping this small part keeps the motor, battery and controller you already own.

✅ Cable tie, not a bracket The body is held by a cable tie around the axle, so nothing is drilled and no bracket has to be sourced.

✅ Two sides to choose Left and right installation versions are offered, so the one your frame and cable route allow is the one to order.

Before ordering, trace the lead from the old sensor back to the controller and look at the plug. This part ends in an SM-3Y connector on a three-wire lead, and the twelve outputs are what the controller reads to decide when to add assistance.

Fitting runs in a short sequence: the sensor goes onto the left axle and is tied down with a cable tie, the two pieces of the magnet plate are joined and held with a circlip, and the plug goes into the controller. No crank puller is needed, which is what makes this a home job rather than a workshop booking.

Two versions exist, left and right, and KT-D12L is the left one. No IP rating is stated for this part, so it is not sold here as a waterproof item and prolonged soaking or a pressure washer is best avoided.

Technical details

• Model: KT-D12L, left-side installation
• Signal outputs: 12
• Interface: SM-3Y, three-wire lead
• Mounting: on the e-bike axle, crank stays in place
• Fixing: cable tie around the sensor body
• Magnet plate: two pieces, held with a circlip
• Variants: 2, left (KT-D12L) and right installation
• Pack contents: sensor and magnet plate; cable tie inclusion not confirmed
• Water resistance: no IP rating stated

Match the plug and the side to your bike, then fit the sensor and ride.

See more: explore more bicycle accessories