code 80
throttle sense voltage is out of range

first thing to try is to run the learn calibration on the control handle

you can also go into maintenance menu and run test A3 on the throttle pot to see how it is reacting. The reading should be a stable reading
Full forward position - 0.4v to 1.5v
Neutral Position - 2.4v to 2.6v
Full reverse position - 3.5v to 4.6v

the sweep should be uniform without any large jumps in readings and when in neutral the reading should be stable.

if it will not learn and stay set then the pot is most likely bad.
there are other things that can set this code as well but this is the most common reason.

now for code 84
brake is misadjusted (loose)
during self test the TMM pulses the drive motor and if the brake is loose it moves the encoder and senses movement and triggers the code 84.
also check the encoder mount and set screws on the coupling at the stem. If any of this is loose tighten them.