Diagnosis
Error E-03 indicates a communication fault between the throttle and the main controller.
How to Fix It
Power the scooter off. Open the deck near the handlebars. Check the throttle connector (a small white plug). Unplug it, check for bent pins or moisture, and reconnect it firmly. Secure any loose wiring. Power back on.
If That Didn't Work
The throttle unit itself may have failed. You will need to replace the thumb throttle assembly. This requires soldering or using waterproof connectors.
Heads Up
Do not attempt to bypass the throttle signal. A faulty throttle can cause uncontrolled acceleration.