Bad wiring, DTR1 defect, Current limit set to low, Defective DD2/DD2, defective driver board, defective current sensor or failed logics.

My expierence is that F5 is usually a defective transistor due to a bad drive motor> higher resistance of the motor and power cables (or bad carbon brushes, damaged collectors) lead to excessive currents wich could lead to faulty transistor (DTR1).
Also wise to check the setting of the current sensor, they can be adjusted with a small internal potmeter.

Lots of options...

F5 i don´t know.
Anyone means what is FS error in the display of B18T?
best regards

a little update, the error is gone and comes only every few days.

Error code F5 (not flashing)
Any one has a manual?

FA Fault, is steer angle problem.
F5 is left drive motor no voltage or loose wiring. Possibly no voltage to transistor
F5 flashing is same as above but right motor
assure all connections are clean and tight