Unless it detires (cant spell) from keeping the car emission friendly and they can prove there TOO loud, than YES they are Illegal in california, but seeing how EVERY truck in cali has mufflers and not to mention the diesels and rice ...Tell him he needs to start pulling every body else over ! THE ONLY illegal part would be an O/R pipe.... The only other way would be the SOUND being to loud, but then he would have to have two other CHP's around with a DB tester and nothing within a 200 yard radius around to test to see if you were above the legaly allowed 120 DB's, Brother is a cop,. If he want to be a DCK about it take it to a judge and youll bw walking away laughing ! I asked my brother this ? when I saw the post and he said the cop was more than likly really really bored and thought you would be an easy target to BS ! Mufflers in cali are TOO hard to right tickets for they use it as an excuse to see if your running an O/R pipe ! ( CHP brothers last name - badge number 3246 )