Do I need to have a medical card if I AM driving a commercial vehicle for a buddy to his house in ca?

Yes, you need it. Even if you're not getting paid, you also need to run a logbook.

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In general this is true, but if you are operating within a 50-mile radius of your buddy's house (maybe you're bringing the truck from a mechanic 20 miles from his home) you don't need a medical card or a CDL. They did this for farmers, so the farmer's 16-year-old kid can drive crops to the point of delivery.

Having said that, you'd be safer to have a CDL and medical card because if you get pulled over the cop is going to work really hard to bust you for driving a CMV without all the necessary paperwork.