All cars live in a metal cage. Any car grounded to the earth, for example by a metal stake and a jumper cable connecting the chassis and the stake, probable would be drivable later. Cars with no ground could be damaged. The EMP research by US Law Enforcement has established guide-lines for deploying EMP weapons, however most proposed weapons to disable the ignition systems were rejected as unreliable or useless due to the natural shielding of the auto chassis. Another consideration is that EMP may have a large voltage but almost NO current. Large voltages with no current can not travel very far. Often, the interference within the engine compartment of a car is subjected to many times the EMR of an EMP. As such, the modules are designed to withstand EMRs. The detonation would have to be VERY close and intense to knock them out. It would probable be advisable to reboot them before attempting to use them.