Firing a fully charged Plasma Pistol shot at a vehicle does not EMP the vehicle. There is talk about this being intentional, but I can only hope it is a bug.
There is also talk about this being a bug ha as the bots can EMP you with it and sometimes when you use it it does nothing Vs enemy players.
Hopefully just a bug, it makes it worth picking up if it is anti vehicle.
Its pretty much useless then