..or you can buy a OBD reader on Amazon. Example:
https://www.amazon.com/OBDLink-Bluetooth-Professional-Grade-Diagnostic-Performance/dp/B07JFRFJG6/
Alpha OBD is the most recommended one as it can do so much more.
CP4 has always been an issue ( a bit overblown sometimes)... the Duramax LML guys migrate to a Cp3 using a conversion kit a lot to avoid the failure and bombing the entire fuel system.
The EcoDiesel performance market is just to small for manufactures to create "kits"etc.. plus what @Tremper126 said, the latest EPA "stuff" really puts a hurt on performance and diesels in general.
Welcome to the forum.. the good news, you'll have a very nice truck with a warranty. You can't really beat that..
I'm still hesitant to recommend a EcoDiesel out of warranty or really well over 100K, just a ticking time bomb unfortunately.