S866 code list · S866 Display

E03 Error on S866 Display

What it means + how to fix it Commonly reported

Quick answer

E03 on the S866 means “Power assist sensor (PAS) failure.” Most likely cause: the pedal-assist sensor's magnet ring has slipped or cracked, or its cable is damaged. Try this first: turn it off and on again.

The S866 table marks this code as "not implemented" on that version, so it may never appear on your S866.

Try this first

Free, and each takes under 5 minutes.

Turn it off and on again
Pedal forward for a full turn

In plain English

The pedal-assist (PAS) sensor watches your cranks turn and tells the controller to help. If its magnet ring has slipped or cracked, the gap is too big, or its cable is damaged, the controller can't tell you're pedaling.

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.

1Turn 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.
2Pedal forward for a full turnFree PAS sensors only detect forward pedaling. Ride off and pedal a full turn or two before expecting help.
3Check 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.
4Unplug 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.
5Dry 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.
6Have 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
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.

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