The “car wash mode” just does a few things that are important to an auto car wash: allows the vehicle to roll in neutral (so the tire pushers can work) without shifting to park, turns off auto wipers, disables the charge port from opening, and disables any of the assistants so they don’t potentially freak out from spraying water and moving components nearby. Seems like this is a simple CYA statement so if the car wash rips off the charging door or windshield wipers that Tesla isn’t liable. Seems quite reasonable to me.