Yes--but only if they have "probable cause" to believe that your car contains evidence of a California felony.
In most cases, police need a warrant to search your residence or office. But cars are different.
In interpreting the Fourth Amendment's ban on "unreasonable searches and seizures," our courts have decided that cars are less worthy of protection than other spaces.
This is partly because they are so easy to move--and so may be moved out of a law enforcement agency's jurisdiction before officers have time to get a warrant.
It's also because we are considered to have less of a right to privacy in our cars.
In any event, the "vehicle exception" to the warrant rule in California allows police to search your car--but only if they have "probable cause" to believe that the car contains contraband and/or other evidence regarding a felony that has been committed.
A police search of a vehicle that is done without probable cause is invalid--and evidence obtained from that search cannot be used to support charges against a defendant. Learn more about California search and seizure laws and if police may search homes without a warrant in California.