Cars are pretty much traveling entertainment systems these days, so I'm sure most of it isn't "mission critical" code, but here's a decent seeming source:
I doubt that the EEPROM is holding all the code these days. For the most part, it's probably holding small sub-routines, or even just LUT's for mapping the parameters of the control logic.
The EEPROMs I've seen in relatively modern stuff top out around 2MB of mostly maps.
Someone below points out it's mostly entertainment systems.