I think you're right about gc.d

Hi , the controller say's the traction pedal are not in zero position , you can test it with lift or press the pedal little bit and then set the keyswitch on. You can find behind the potmeter under floorplate a plastic gear systeem ,check this for malfunction

Hi

It's just basic information, that there's some problem with the traction.
When you restart the truck (the best is to reset it in order: the key, the red button, the battery plug and back) and the message remains it means there are traction problems. This may be some sensor, poti or even the traction module.
You need diagnostic software to verify it.

Which generation is the truck?
On some newer generations you can call on your display the errors from your system.