Hey RV_living, I'm guilty. Semper Fi. California has the strictest emission controls in the nation. However, an older diesel should be able to pass the controls, unless it is really old (1990's). The older diesel's were not computer controlled and that may be a problem. The new fuels (Ultra Low Sulfur Diesel) should burn cleaner, but who knows what kind of emission standards California has. That's why I just visit there. I have been a resident 2 times. I was shocked at the red tape and taxes involved with vehicle registration.
Normally it has never been an issue but now they are getting very strict on the opacity. That is where most of our friends have failed and the repairs have been super costly. We are still doing more research on the topic because it just seems outrageous how much it costs to get the vehicle back in tolerance!