[TylerE]

Notable, however, California, the largest vehicle market by some margin, still requires sniffer tests.

[CableNinja]

Only on older cars, which do not have OBDII. OBDI and before that require a sniffer. OBDII has enough sensors that the sniffer isnt needed. Am in CA, and only my foxbody ever got a sniff test. All of my other (newer) cars, the sniffer wasnt used

[AvocadosNombre]

* for vehicles model year 1999 and older, not more modern ones.