ENGWE's own error codes
These codes come from ENGWE's official sources, listed at the bottom of the page. ENGWE's 3.0 manuals say riders must be 14 years or older. If your screen shows a code that isn't on this list, your bike may use a different display: find your display .
Quick answer
E31 on the ENGWE EP-2 3.0 and L20 3.0 means “Control unit fail.” Most likely cause: a power or connection problem reaching the controller, or a controller failure. Try this first: turn it off and on again.
EP-2 3.0 manual wording. The L20 3.0 manual says "controller fault".
Code meanings vary by brand. The same number can mean different things on different displays and controllers. Check your bike's manual to confirm.
About the ENGWE EP-2 3.0 and L20 3.0
Both 3.0 manuals print the same table. The only wording difference is E31: "Control unit fail" (EP-2 3.0) and "controller fault" (L20 3.0). source Older EP-2 and L20 versions are not covered by this list. source
In plain English
The controller is the part that takes power from the battery and feeds it to the motor. This code means it has flagged a problem with itself. Sometimes that's a real failure, but low battery voltage, a loose connection, water or heat can trigger it, so rule those out first.
Step-by-step checklist
Reset
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.
As an Amazon Associate I earn from qualifying purchases. Steps marked "affiliate link" link to Amazon.
1 Turn it off and on again Free 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.
2 Fully charge the battery Free Plug in the charger and charge until it shows complete (usually a green light), then switch on and test again.
3 Let it cool down Free If it happened after a long climb or hard riding, switch off and let the bike cool before riding again.
4 Unplug and check the main connectors Easy 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. Melted or burnt plastic means stop and see a shop. Clean green corrosion with electrical contact cleaner and let it dry fully, then push the plug back together with the arrows lined up.
Need it? Electrical contact cleaner spray on Amazon (affiliate link)
5 Wiggle-test the wiring (motor off) Easy Switch the display on, but don't run the motor. Gently wiggle each small connector and cable one at a time, by the handlebar and along the frame, and watch the display. If it flickers, resets or shows a code, you've found the loose spot. Switch off and remove the battery before you reseat it. Never wiggle wires while the wheel is spinning, and leave the thick motor and battery plugs to a shop.
6 Dry the bike out if it got wet Moderate 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. Don't use a heat gun or put the bike next to a heater.
7 Have the controller tested Shop job If the wiring checks out, the controller may be faulty. A shop can test it and replace it if needed.
⚠ When to stop and get a shop
Stop and see a shop if the controller is hot to the touch, smells burnt, or has melted plastic on any connector. Don't open the controller or cut into the main wiring harness.
Anything inside the battery, the controller, or the thick high-power motor wires is a job for a qualified e-bike shop.
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.
Electrical contact cleaner spray Cleans dirt and corrosion from connector pins and battery contacts.
View on Amazon Dielectric grease A thin coat on connector seals helps keep water out after you clean them.
View on Amazon Digital multimeter Checks whether wires are broken and measures voltage.
View on Amazon
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: Controller
Sources
Written and checked by Kazolt against the sources above. Last checked: October 23, 2026. How we write our fixes
Does E31 mean something different on your bike? Let us know so we can fix this page.