The 4th amendment protects people from unreasonable searches and seizures. As you can tell only UNREASONABLE searches are protected. One of the ways an officer can reasonably search a vehicle is to obtain a search warrant from a magistrate. The warrant must be based on probable cause and the underlying facts must be described withparticularity.
Search warrant = probable cause + particularity. In many situations, a search was conducted without a warrant. If your vehicle was searched without a warrant, the search must fall within recognized exceptions to be reasonable.
Exceptions to a warrant requirement (only the exceptions related to the question posed are explained below)
Consent is one of the most common ways for an officer to search a vehicle without a warrant. If you allow the officers to search your vehicle, then he/she is allowed to search the vehicle. The consent must still be voluntary and intelligent. This means that the officer cannot obtain your consent through duress or a threat.
A search incident to a lawful arrest is another exception to a warrant requirement. If you are being arrested for a marijuana DUI, then the car can be searched if an arrestee is unsecured and within reaching distance to a vehicle OR the officer has a reasonable belief the evidence to the crime of arrest is inside the vehicle. So if you are being arrested for DUI of marijuana, a police officer may likely search the vehicle for marijuana.
Inventory search. If you are being arrested and taken to the police station, then the police may search the entire vehicle and your personal belongings.
***Plain Smell Doctrine (coupled with an Automobile Exception). A police officer is most likely to rely on this exception in the aforementioned question, given that you do not consent and you are not being arrested for another crime. This doctrine will apply in the situation where a police officer smells marijuana odors from a vehicle. If the officer is trained to recognize marijuana smell, the incriminating character will be immediately apparent to him. If the smell is strong enough that a police officer has probable cause to believe that marijuana is in the vehicle, then he is allowed to search it.
***Thus, a question whether police officers can search a car if they smell marijuana outside of the vehicle can only be answered with the underlying facts in your situation. The weight of the evidence will determine the authority. How much smell was coming from the car? Did you smoke in the car? If so, how long ago have you smoked? Was marijuana packaged? How was marijuana packaged? Did police use a K-9? Etc.
*** RECENT DEVELOPMENT IN CALIFORNIA. 3/11/2014. Odor of burnt marijuana emanating from a vehicle and the observation of burnt marijuana in a pipe inside the vehicle create probable cause to search that vehicle pursuant to the automobile exception to the warrant requirement. Nonmedical marijuana is “contraband” and thus subject to seizure even when possessed in amounts less than that which makes possession a crime. People v. Waxler – filed March 11, 2014, First District, Div. Five Cite as 2014 S.O.S. A137796. Full text http://www.metnews.com/sos.cgi?0314//A137796
***The application of this doctrine in situations where the arrestee has a medical marijuana card is confusing. Courts have found an implied defense to the transportation of medical marijuana when the “quantity transported and the method, timing and distance of the transportation are reasonably related to the patient’s current medical needs.” (People v. Trippet (1997) 56 Cal.App.4th 1532, 1551. Please call our offices to discuss your situation.
Note that the police officer does not have to find marijuana during his search of the vehicle. If the officer finds other incriminating evidence during a reasonable search, then that evidence will still be used against you in court.