I find the plugs to the steer sensors get bad. I have replaced a few steer sensor looms recently.

You have to Check the electronic circuit or rear wheel proximity switches.

Check the rear proximity switches and don't press the brake pedal when go to yhe sideward mode.

Any updates on this issue? I am having a similar issue with a C6000. The rear wheel will not respond to input from the directional switch. The front out rigger wheels respond normally, (90 degree or 0 degrees depending on the placement of the switch). The relays all seem to be ok. I did notice that if I unplug the steering solenoid under the operator compartment, that I lose functionality to the front wheels and gain function back in the rear.
Now... if I drive the machine normal, I do have steering abilities, This issue seems to only be associated with the directional control switch. I did reach out to Combilift today but haven't been given much insight yet.

first verify that it is actually bad, check the spacing (clearance) between the sensor and its trip point. Also you can use a screwdriver or some other metallic magnetic condutive tool to put against the sensor (orange/yellow) end and insure it is actually functional or not. if it is working it should light up the small led lights located around the end of it where the cable connects to it.
if they do not light up then you should trace the cable back to where it connects into the main control circuit and check the circuit there. You can disconnect it and check it at the connections there to verify if the sensor is actually bad. If it checks good continuity when triggering it then your problem is somewhere else before that point in the circuit.
back probing circuits can be a pain on these units so having a service manual and appropriate schematics are very helpful.

First check the fuses on the panel on the operator control panel and make sure they are all good. Don't assume by looking at them that they are ok, use a vom and physically check them.

you'll need an electrical schematic for this unit before you can trace and find the problem responsible for the power loss. Most functions are powered and/or controlled through relays on these units.