What is the test for obtaining a warrant to search a vehicle without a search warrant?

"Chambers (Chambers v. Maroney, 399 U.S. 42, 90 S.Ct. 1975, 26 L.Ed.2d 419) and McKinnon (People v. McKinnon, 7 Cal.3d 899, 103 Cal.Rptr. 897, 500 P.2d 1097) establish the rule that when there is probable cause to believe that an automobile stopped on a highway contains contraband, evidence of a crime, or was itself an instrumentality of the commission of one, law enforcement officers need not obtain a warrant before conducting a search since there is no distinction of constitutional proportion between an immediate search on probable cause without a warrant and the automobile's immobilization until one is secured." (Fn. omitted.)