This problem gave me problems for about 4 months. We were on extended travel through the southern states from Idaho to Florida. The engine light came on in Texas. I took it to a GMC dealer and he check all the codes and there were several. He cleared them and told up to go to a dealer when the light came on again. I took it to another dealer after the engine light came on again about 700 miles down the road. Again several codes came up and was told same thing when light comes on got to dealer to check. We had to leave Florida quickly because all RV parks were being closed because of the Virus. We drove from Florida to Idaho in 4 days. I took it to a independent diesel specialist. He said the whole DEF systems was no longer working and it cost me 1500. I paid this out of my pocket because it was out of warranty. I had a 2007 PU with 200,000 miles with no problems and this one was problems from about 80000 mile on.

Update from Sep 30, 2021: Engine light was a defective sensor on the low pressure rail of the fuel system. Got it replaced and instantly sold the truck and will no longer by GM product. bought 5 new vehicles two being diesels. They wouldnot consede they had a serious problem and after 100,000 miles and knowing the issues with that fuel pump and a bullinten to dealers to replace with up grade the dealership put the old style pump back. That is poor business.