Check the function of the control unit with clean water. If the nozzles drip when the main ON/OFF is closed, it is likely that the valve ball and seat are worn. Change if necessary.
The boom section valves must also close completely. Open the main ON/OFF and all section valves with the pump working. When the return hose from the constant pressure valves is removed and the housing drained, no water must appear from the valves. If the section valves are not completely sealed, the valve cone should be replaced. Failure to do so reduces capacity and will show incorrect data on the sprayer computer.
Finally all movable parts of the control unit operating handles should be lubricated with oil.