But it's not a commercial truck

Michael Gunter of Kansas City won a reversal in U.S. v. Herrera reversing a conviction for possessing cocaine with intent to distribute out of Kansas. The Tenth Circuit noted that it did not need to decide whether an administrative scheme that purports to allow searches of commercial vehicles without any reason is constitutional because Mr. Herrera's truck was not a commercial vehicle:

Because the Government sought to justify its stopping Herrera in this case based only upon a regulatory scheme permitting random administrative inspections of commercial vehicles, the authority for that stop must come from that regulatory scheme. And because Herrera's truck did not fall within the class of vehicles subject to that regulatory scheme's random inspections, the state trooper in this case had no authority to stop Herrera. The trooper's seizure of Herrera, therefore, violated the Fourth Amendment.

The Tenth Circuit also held that an improper search could not be saved by the good-faith doctrine when the mistake of fact was the law enforcement officer's:

Because the very justification for allowing warrantless administrative searches is not present here, we do not believe it is appropriate under these circumstances to expand the regulatory search concept further by upholding an unauthorized administrative search because of the officer's mistaken good-faith factual belief (not shared by the person being searched) that the vehicle being searched was a commercial vehicle subject to an administrative search.