Doosan 110 forklift showing Faulty code D4

I have a 110 doosan forrklift which was sometimes disengaging from gears to neutral nd it was showing "D4 "faulty and i found out that it was the Alternator which was overcharging .31volts at idling. Then the transmission Ecm shuts down and put the transmission in neutral position.
Now i fixed the alternator the problem is solved but now i need some schooling on this alternator to transmission ecm . How do they link