Hi Leon,

My company repairs a lot of these type of controllers (check your email).

When does the fault happen, is it when the truck is driving? or does it happen when the truck is first switched on? you may have an intermittent earth fault on the drive or hydraulic motor, or the motor cables it may be just a build up of carbon dust from the brushes in the motors causing the the controller to give the fault code. Also check the line contactor tips.
Regards
Shane