I have 2004 stralis 480 with cursor 13 engine but the driving wheel wont turn if the truck are loaded unless moving but if its empty or free of load it turn easily
I’ve moved your post to this forum where I think it will receive more views and responses.
I know nothing of the Stralia particularly, but first check with power steering faults would be fluid levels in reservoir, visible leaks from pipes, noises from pump when on lock.
4x2 or 6x2?