Problem · 850C Display

E-Bike Pedal Assist Not Working (850C)

Causes + how to fix it

Quick answer

The motor doesn't help when you pedal. Most likely cause: assist level 0, a brake lever or sensor that's on, or a pedal-assist sensor that's out of place. Try this first: set the assist level to 1 or higher.

Try this first

Free, and each takes under 5 minutes.

Set the assist level to 1 or higher
Check the brake levers spring back
Pedal forward for a full turn

In plain English

Pedal assist relies on a sensor that detects your cranks turning (or, on torque-sensing bikes, how hard you push). If the assist level is 0, a brake sensor is active, the sensor's magnet ring has slipped or cracked, or its cable is damaged, the motor won't help. If the throttle still works, the motor and battery are fine and the problem is almost certainly the sensor or a setting.

Step-by-step checklist

Work from the top. Steps go from free and easy to shop jobs. Switch the bike off before touching any connector. Tick each step as you go. Your progress is saved on this device.

1Set the assist level to 1 or higherFree Level 0 usually means no motor help. Raise the level and try again.
2Check the brake levers spring backFree Squeeze and release each brake lever. Both should snap all the way back. A lever that stays slightly pulled keeps the motor switched off.
3Pedal forward for a full turnFree Most sensors need a half to a full turn of forward pedaling before the motor kicks in. Pedaling backward does nothing.
4Turn it off and on againFree Switch the display off, wait 30 seconds, then switch it back on. If the code clears, note what you were doing when it appeared, in case it comes back.
5Check the pedal-assist sensorEasy On most hub-motor kits, a ring of magnets on the crank spins past a small sensor. Make sure the ring isn't cracked, wobbly or rubbing, the gap to the sensor is small and even, and the cable isn't damaged. Mid-drive motors have this sensor built in, so skip this step on those.
6Unplug and check the main connectorsEasy Switch off and remove the battery. Find the round waterproof plugs along the cables (usually near the handlebar, down the frame and near the motor). Pull each one apart, look for bent pins, water, green corrosion or melted plastic, then push it back together fully with the arrows lined up.
7Dry the bike out if it got wetModerate If the problem started after rain or washing, remove the battery and leave the bike somewhere warm and dry for 24 to 48 hours, then test again.
8Have the sensor replacedShop job If the sensor is damaged or still faulty after these checks, a shop can test and replace it.

Parts you might need

As an Amazon Associate I earn from qualifying purchases. These links go straight to Amazon.

Only buy a part if the free steps didn't fix it. Always match the voltage and connector type to your bike.

Pedal-assist (PAS) sensor
Replaces a cracked magnet ring or faulty sensor on hub-motor kits. Match the connector.
Link coming soon
Brake cutoff sensors
Replaces a faulty brake sensor that keeps cutting motor power.
Link coming soon
Electrical contact cleaner spray
Cleans dirt and corrosion from connector pins and battery contacts.
Link coming soon

Still not fixed?

Pages to try next:

When it's time for a shop: if you've worked through every step and the problem is still there, take the bike to an e-bike shop. Bring your notes on when it happens, plus the code and your error history.

Words on this page: PAS (pedal-assist sensor)Throttle Torque sensor