5th edition: the device rating of consumer grade goods (which sounds it it describes a Ford Americar, as opposed to being say cheap and disposable or purpose-built for police or military use...) is 2. And you sub in device rating for missing stats, ergo it'll roll 2+2 dice to resist your decker's shenanigans. (unless slaved to a device or host with a better dice pool, of course...). If all you need is to open the door (i.e. you don't plan on driving it) you only need 1 or 2 marks for the control device, depending on whether you call opening a car door a free or a simple action. If you intend to DRIVE the car after you open the door, then yes the hacker needs 3 marks.
6th edition: devices that lack D/F have 0s. However, in the specific case of vehicles/drones, you sub in Pilot in place of mental attributes, so it'll at least roll that when willpower or intuition is invoked. As with 5th edition, if the car is protected by a PAN or Host, you'll use the better dice. If all you want to do is make the car door open, you can Spoof Command with outsider access. If you want to drive the car around after you open the door, then you'll need User access.