Depends if your having a drive problem (wheels not driving/turning) or mode change problem (wheels not steering to side mode/forward mode) please be more clear.

If the truck is in side mode when you select forward mode and the front wheels turn from side mode to forward mode but not the rear wheel you possibly have an issue with your prox sensors on the Front wheels. Check to make sure front 0 degree prox sensor is lighting up and sending signal back to plc/relay. And that stop bolts are adjusted properly.

If your truck is in forward mode and the rear wheel turns to side mode but not the front wheels you have an issue either with the 90 degree prox on the rear wheel, stop bolt adjustment, 6port control relay, 6 port steering vlave or wiring. (Starting from most common to least)

If your having a drive problem where the front wheels turn forward and reverse but the rear wheel does not you may be into a brake problem (if the rear drive unit has a brake). If there is no brake remember these acr like an open diff if jacked up. Wheel with least resistance will turn. If no wheels will drive and you have checked all electrical you may have a bad drive unit.

Need more information if you want more help.