Also called: controller, ECU
What it does
It reads the sensors, the throttle, the brake switches and your assist level, and sets the motor's power. On mid-drives it's built into the drive unit; on many hub-motor bikes it's a separate box on the frame.
Signs of a problem
- Motor stops but the display stays on
- Error codes about communication or overcurrent
- A burning smell or heat from the controller box
Safe things to check
- Check the controller's plugs are fully connected and dry. Look; don't pull hard.
- Any burning smell: stop, switch off and don't ride.
Looking after it
- Keep water away from controller connectors.
- Controllers aren't a home repair; changing one usually needs the right model and settings.