Any unshielded electronic system can be fried by EMP...even if they are not in operation.
It is the initial burst of powerful electromagnetic energy that does the damage.
Cell phones, radios, hard line telephone systems, electic power grides, wind generators, solar power systems, satellites and many other systems would be fried.
One very large hydrogen bomb detonated high in the atmosphere above the US would create havoc with just about every system we have.
Any motor vehicle that has a computer in it would be non-mission capable unless it had been in a protected environment when the blast went off.
There might be limited protection in tunnels, mines or anywhere the EMP could not penetrate.
Any modern aircraft in the air at the time of the blast would be screwed....especially if they were fly by wire or had computer controlled guidance and flight systems, not to mention loss of radar and Air Traffic Control.
The banking system would be destroyed and all the money out in cyberspace would cease to exist.
No one would be able to get any money from any bank. Wouldn't take long for TSHTF.
The good news is that there would be plenty of fuel because 95 percent of the vehicles on the road would not be able to run.