That ain't true for California, or at least it wasn't.

In 2000, the last year that I lived in San Diego, the DMV used cheat sheets with pictures to see if anything had been removed or otherwise modified, both under the hood and under the chassis.

 

Every place is different I suppose. The places I have been through had excessive noise meters and a sniffer to measure the levels. They didn't care about anything else. Pass or fail based on what came out of the pipe based on pollution and noise levels. California seems to be tough to drive anything but a bicycle. The politicians should be praised for their unbelievable forethought and wisdom.

 

Its actually (for a diesel) easier than most states.

They do a visual (this is where they would pick up a missing DPF shell), check for any hidden codes with an OBDII scanner, then do a "snap" test. Which is just a blip of the throttle up to 75% of max rpm's, if a black smoke cloud lingers for longer than 10s (I think) it will fail - if you don't have a hot tune in your truck when you get it tested, it will pass


My 7.3l has a 4" down pipe - to a 5" exhaust that drops out under the bed. No muffler, no cats (admittedly, my 7.3 wasn't fitted with them from the factory) - and the truck is stupidly loud. It passes.

 

How often do you guys have to go in for these tests??

 

Once every 2 years in CA.