I'm going to take some guesses here. The common problems were the lift valve slamming to one end of it's travel. There is a motor on the end of the valve with a screwdriver slot in the end of it. You can turn the motor with a screwdriver and see the valve move. Center the valve. The valve is on the right side wall of the power unit.

Unplug all the plugs and re install them.

Look for fault lights on any of the cards. There is a box on the platform and the base. Some of the cards are interchangable.

Check your chain slack and chain broken switches. There are four under the seat. I had a few of the chain slack switches go bad.
Check the height encoder. It is on a spool that is spring loaded or retracted. It is basically a very small steel cable that attaches to a switch in the in the base of the truck under the platform. If the cable hangs up and goes slack, it will close the switch and give the wrench light.

I you leave the drive/tow switch in the tow position, you will get a wrench.

These were the common problems. Beyond that, you need the Crown service terminal and book for the terminal.