I don't understand how California detected this. The one time I had to take my 2010 Jetta turbo diesel for a smog check, the inspection was ENTIRELY visual. The inspector did not insert a probe into the tailpipe. He did plug the test rig into the OBD-II port under the steering column and turn the key to the accessory position (presumably to electronically capture the VIN), but that's it. I even asked him at the end i…
The drive-by inspection doesn't require the co-operation of the driver or car, so is harder to game by detecting you are being tested.