Keith....I had a 400 ISL in my 2005 Diplomat that ran flawlessly for 75K miles before I traded it on my new coach with the 450 ISL. First big trip, I get a check engine light (EGR over temp). By the time I get home, it's out and wrote it off as a glitch. Next trip, I get the same light again. I took it into Cummins. They cleaned and serviced the EGR, which only had 6K miles, reflashed the computer and said it was fine. After that, I read a post by another ISL owner who said that he makes sure the gauges sweep before he starts the coach. Since then, no issues. While in Yosemite Valley last year, I started it before the gauges swept and sure enough, it threw the code, but went out in a few miles.
Don & Mary
2019 Newmar Dutch Star 4018 (Freightliner)
2019 Ford Raptor