3582 is a four hour troubleshooting tree where it test everything in your scr system one component at a time. It usually results in the replacement of the catalyst. If your catalyst has never been changed it is probably an obsolete version which will require a harness to delete the amonia sensor (NH3 sensor).
This is a very common problem on Cummins scr catalyst from 2010-2012. If you have had any def system issues it could of washed your brick which will also require replacement. If the def nozzle was leaking or if your a local guy who idles a lot you could also have plugging in you decomposition tube. Caused by crystalized DEF.
I suggest taking it to a reputable shop and have them do the diagnostic for the 3582.