I always get the print out of any service done, but I am unaware of whether the codes are on there I guess I can look into that.
Side-note... this is my second GMC truck this year. The first one had service trailer brake system before I drove it off the lot. They took it back there, worked on it, 30 min later said it was fixed, I signed the paper work, and took off. Literally 5 miles down the road, it popped back up. I took it back and they gave me a loaner to go grab lunch while they looked at it. Came back from lunch and they said it was fixed. Took it home (75 miles away) bout 20 miles from my house it popped back up. They decided to swap me with another new truck even, which is the one they are working on. Now it's this is the 4th time it's been here... I should probably get a part time sales job I guess. I'm here enough, might as well get paid.