Imagine driving down the road one night, and police pull your car over. The officer states that you were speeding. The police do not have a warrant to search the vehicle, but rather, the police tell you that they only need a "probable cause" to search your car. Do the police have probable cause to search your vehicle? No. So, when would the police have probable cause to search your car?
Courts usually find probable cause when there is a reasonable basis for believing that a crime may have been committed (for an arrest) or when evidence of the crime is present in the place to be searched (for a search).
Motor Vehicle. “[W]hen an automobile is stopped in a public place [a search can be conducted] with probable cause, [and] no more exigent circumstances are required by art. 14 beyond the inherent mobility of an automobile itself.” Commonwealth v. Motta, 424 Mass. 117, 122 (1997). Even where a motor vehicle is involved, however, the authority to conduct a warrantless search upon probable cause is not of unlimited duration. Commonwealth v. Agosto, 428 Mass. 31, 34 (1998).
Containers. Under both the Fourth Amendment and Article 14, if there is probable cause to search a motor vehicle, justification extends to search all containers, open or closed, found within it. Under both the Fourth Amendment and Article 14, the search is circumscribed by the object or objects of the search. The search may be no greater than is necessary to locate the objects sought. Commonwealth v. Moses, 408 Mass. 136, 145 (1990).
Persons. In certain circumstances, when police have probable cause to believe that a suspect is concealing evidence of a crime, a warrantless search of the person is permissible. The search “must be limited in scope to those areas of his person and clothing” that could reasonably be thought to contain the items sought. Commonwealth v. Skea, 18 Mass. App. Ct. 685, 701 (1984).
Exceptions to probable cause follow: Consent to Search ... Plain View Evidence. ... Hot Pursuit. ... Search Incident to Arrest (which is limited). ... Exigent Circumstances. ... and Inadvertent Discovery.
In summation, the mere speeding of a car does not conclude that the driver had contraband in the car. However, if the police officer finds a passenger holding an illegal substances in plain view, the police will likely have probable cause to search the vehicle, and the containers therein. If there's probable cause that the passenger is hiding contraband, then they will also be subject to search.