It varies, in order of most CPU usage increase to least:
Driving (Or the vehicle moving at all)
Fueling/charging (There’s over 40 tanks for gas alone)
Repairing/Modifying
Accessing Cargo
Idle
Any time the vehicle is on screen there’s a noticeable frame rate loss and a CPU usage increase of almost 10% on my shitty laptop. (1.6 Intel Pentium GHz Dual Core) Is CDDA built with multi-core in mind? I know DF isn’t and it actually runs worse on multi-core systems (though it’s negligible on higher-end multi-core systems).