my guess is the machine might be in what we call 'limp mode'. This is set when there is a problem with the machine and until the problem is corrected the 'limp mode' will remain. It's like a self protection mode the truck goes into to help cool or keep the operator from driving too fast.

After pondering those brake and foot switch codes i'm thinking there may be an issue with the foot switches under the deadman pedal. Here the mfca built trucks had alot of issues with those switches, mfca came out with updated parts for those switches so now when we run across one giving issues related to the deadman circuit we always replace those switches first. One switch is a brake release switch and the other triggers the controller(s) to turn on.

You might want to check the brake unit and make sure it is releasing, the slow drive might be the brake dragging? Unlikely but it's something to check also. If an electric brake you should clearly hear it pop when it applies and also hear it when it releases.

As for changing the speeds, on certain models the mfca trucks had dash has buttons on it allowing the operator to change operation modes... does this unit have any button indicators? Some models didnt though and the speeds could only be changed using the software program. The one version (first gen AC drive) of that truck with the buttons on the dash had the zapi system in it, the other with the plain display used a sauer danfoss system. I'm thinking the newer models now have a danaher system in it?

Just a few thoughts on this....