Updated April 2026
Jump to Section
This is the most commonly reported issue with Surface 604 bikes. Your throttle works fine — you twist it and the motor engages — but pedal assist does nothing. You pedal and the motor doesn't kick in at any PAS level.
In almost every case, this is caused by one of three things: a stuck brake inhibitor, a loose torque sensor connection, or a failed torque sensor. Here's how to diagnose it step by step.
This is the most overlooked cause. Squeeze and firmly release both brake levers several times. A stuck brake lever keeps the motor inhibitor engaged, which silently cuts all pedal assist power — with no error code displayed.
To confirm: disconnect the brake inhibitor wires one at a time (small 2-pin connectors near each brake lever). If pedal assist returns after disconnecting one, that brake's inhibitor switch is stuck or faulty.
Locate the torque sensor cable at the rear dropout — it's a small green connector on the non-drive side of the rear axle.
This is the definitive test:
If the throttle works fine without the torque sensor plugged in, the torque sensor needs replacement. The dropout torque sensor is a 20-minute replacement with basic tools (Allen keys and a wrench).
The cable running from the torque sensor to the controller can get damaged — especially after a rear tire change. Inspect the full length of the cable for pinched, cut, or frayed wires. If damaged, replace the torque sensor extension cable.
If brake inhibitors are fine, the torque sensor connection is secure, and a new torque sensor doesn't fix it, the controller may need replacement. Contact support with your serial number for next steps.
Was this article helpful?
