Are you getting an error code on the display, or does it appear normal?
If replacing the harness did not help, then the speed sensor may need a slight adjustment - it should only be around a credit card's width away from the motor.
Check that it is in the correct position and has not moved during the movement of the machine.
Hi, just checking in on your question. How did things work out for you?
The speed sensor is located at the front roller near the motor assembly.
The speed sensor is a small device with wirings coming from it see:
Could you attach a photo so I can see?