[stavros]

I don't know much about car tracking specifically, but I really doubt they have anything more than a simple GPS module. If you disable that, you lose fine-grained tracking. You'd still have the phone company triangulating your radio's location, which is lower-resolution, but you may want to disable that as well.

Really, disabling the radio entirely would be your best bet.

[tyingq]

Could be tough. I imagine the bus connections between the gps, radio, and systems needed for the car to operate are often intertwined. Might be easier to find and cut the antenna leads.

[stavros]

Yep, that's one way to disable the radio!