Final answer:
Probable cause to search a vehicle can be established by the odor of illegal drugs, but an expired registration, broken tail light, or driving above the speed limit alone do not provide probable cause for a search.
Step-by-step explanation:
Probable cause for a search of a vehicle can be established in several ways, one of which includes the odor of illegal drugs. The presence of this smell suggests that illegal substances might be in the vehicle, implying a potential violation of drug laws. However, scenarios such as an expired registration, a broken tail light, or the act of driving above the speed limit do not inherently provide probable cause to search a vehicle. They can justify a traffic stop, but a search would require additional indicators of criminal activity or the owner's consent. According to the precedent set in Terry v. Ohio, officers must have a reasonable suspicion of criminal activity to detain or frisk an individual, but they must have probable cause to conduct a vehicle search without a warrant.