Can I use dish soap to wash my car?

It is not recommended. Dish soaps are designed to cut grease aggressively and can strip wax and sealants, leave paint without protection and, with repeated use, dry out rubber and plastic trim. They also provide little lubrication compared with car shampoos. A single wash with dish soap will not ruin paint, and it is sometimes used deliberately to strip old wax before polishing, but a dedicated car shampoo is the better routine choice.