I live in Phoenix, AZ. You will have to get your 300d tested. I believe the rule in Arizona is that only cars older than 1967 regardless if its a diesel or not don't have to be tested. Forced is right about the 20% opacity test. It is fairly easy to pass. The first time I tested my 1984 euro 240d, I got a 4% reading. The next time I ran diesel purge through my system about two days before the test and then had 0%.