I had a mouse make nest under the engine plastic cover piece, and bury itself underneath a lot of the cabling. It gnawed the wiring and I had to buy a new cable (a smaller cable assembly, not the main engine harness) and caused engine light to come on. One of the connectors on the main engine harness was still intact but needed to be re-crimped so I had that done. Total cost around $880 .... They also had to take the intake manifold off to check if they made a nest in there. They had a lot of nuts and poop and pee marks lying inside the engine bay which I had to clean up. You want to clean it up and remove their odor.
The way I took preventative measure is by getting this very loud ultrasound speaker which I leave on in the garage squealing. I also keep the lights on in the garage.
I bought some mouse spray that has this peppermint smell that they don't like. I sprayed around the areas it was hiding in the garage like the walls, and around the entrance area, and around the water pipes. Try to cover up any openings, I'm going to add some wire mesh to a pipe as they might have walked through the pipe.
Bought a lot of poison traps, put one in the garage, and then 3 around the house outside. I think poison traps are okay if you are going to run your cars daily as then they can't just sit in there and die. In beginning run them daily and get them hot, the mouse can't live in there while it's running hot.
I cleaned up the garage, threw away a lot of boxes and moved stuff out. Keep the garage less cluttered, as more clutter the mouse likes it to hide around in.
Pick up any droppings or whatever you see in your garage or car, and clean it out with some soap to remove their smell.
When gone for period of time, I just leave the hood up with a bright light shining on the hood with the ultrasound speaker running, they seem to hate bright lights. And looks like that loud speaker is working. I recommend you just remove the plsatic engine hood cosmetic cover thing, that seems to help provide insulation and shade which they like to hide in.
I have the spring mouse traps, but haven't deployed those. As it seems the above has been effective so far. Will check if the poison bait traps have some of the bait taken up, if so then it shows they're working.
I also heard people use dryer sheets as they hate those smell. You can zip tie a few of those on your electrical wires, and that should keep them away. I haven't had to deploy those yet, as I had a lot of preventative steps above already, but will consider it as it's not too hard. The dryer sheets will have to be swapped out periodically though as they lose their odor so it's annoying.