It likely your ABS pump, it seems to be a common issue sadly. My 2500 is currently at an independent Diesel shop waiting for a used part. If you search around some people are on their 3rd pumps. The dealer told me it would be February at best before I could get a new part, and searching around on the web some people have been waiting a year. I am not happy about how much this will cost.
If your handy you can try and do this yourself, there is some info below. If this happens to me again I am going to DIY it. I am paying the shop way too much for a used replacement part, but it's not the shops fault.
Start by getting a good scanner like the
OBDLink and AlfaOBD (its an app on your Android phone, not sure about Apple). This will give you the exact code. Getting these two cost less then going to the dealer to pay for a diagnostic.
Once you figure that out if its the pump you can try this
service to repair it, however I can not comment on how effective it is. This
thread has a lot of details about what might be the issue.