Generally speaking, automobile searches require probable cause but not warrants. That goes back to a prohibition era SCOTUS case in 1925.
"if the search and seizure without a warrant are made upon probable cause, that is, upon a belief, reasonably arising out of circumstances known to the seizing officer, that an automobile or other vehicle contains that which by law is subject to seizure and destruction, the search and seizure are valid." Carroll vs US
The so-called "motor vehicle exception" to the warrant requirement is based on mobility. The concern was that the car, and the contraband, would be gone before the warrant could be obtained.