Yes. The United States Supreme Court in Florida v. Harris (2013) 568 U.S. 237, 243-250, upheld a warrantless search of a vehicle because a K9 sniff constituted probable cause. In Illinois v. Caballes (2005) 543 U.S. 405, the Supreme Court held that a K9 sniff is not a search and therefore does not implicate the Fourth Amendment.
In recent years, due to the legalization of marijuana in many states, detection of only marijuana does not necessarily provide probable cause to search; it is only one factor in determining probable cause. In those states, then, LE must be able to articulate additional factors other than the “legal” amount of marijuana. The Colorado Supreme Court, for example, in People v. McKnight (2019) 2019 CO 36, held that law enforcement officers must have reasonable suspicion to believe that an item or area contains a drug in violation of state law before deploying a K9 that alerts to marijuana for an exploratory sniff. Colorado goes on to hold that even if a marijuana trained K9 dog alerts, the alert is only a factor in determining probable cause. This is in direct conflict with the United States Supreme Court. Colorado justified the departure by stating that since a marijuana trained K9 could be detecting “legal” activity (personal possession of marijuana) this transforms the “sniff” into a search which needs probable cause to justify it.
California, until recently, was in line with the U.S. Supreme Court; if evidence of marijuana comes to light, LE still has the right to continue to investigate to determine if the marijuana is legally possessed. People v. Waxler (2014) 224 Cal.App.4th 712. Recently, though, in People v. Lee (4th Dist. 2019) 40 Cal.App.5th 853, the court held that since California law now “expressly provides that legal cannabis and related products “are not contraband” and their possession and/or use “shall [not] constitute the basis for detention, search, or arrest,” (Health and Safety Code section 11362.1(c)) the small amount of marijuana found was not probable cause to allow for a search. While Lee was not a K9 case, it has ramifications for K9 sniffs. LE can still use a marijuana trained K9 as California has not eliminated the K9 alert completely. California may, however, be limiting the alert to only a factor in determining probable cause rather than probable cause in and of itself. Therefore, it is critical to document and articulate all the other reasons LE believes that subject is in possession of contraband (which includes marijuana in an illegal form; i.e., too much, BHO lab ingredients, etc). In addition, most K9s are trained in other controlled substances, and LE knows from training and experience that most people who abuse drugs do not limit themselves to just one type of drug; most are poly-substances abusers. A handler does not know what the K9 is alerting on; it could be any other substance in which the K9 is trained. Your report should reflect all factors so the court has a full picture of what the handler encountered in the field.