ERROR 21:

Speed Sensor error

1. Please check to make sure your Speed Sensor and magnet are installed correctly. The magnet must be installed within in 1-2mm of the Speed Sensor with the smooth side of the magnet facing the Speed Sensor. Make sure that the Speed Sensor is fully screwed into the Motor lead plug.

2. If Step 1 does not fix the error, you most likely broke your Speed Sensor and need a new one.