Quick tip GM light duty trucks
When you have a service emissions system message on, after doing a Def DTC repair you will need to do a reductant system malfunction warning test to clear the message.
The problem we are having this time of the year is that the test will not run if the ambient air temperature is below 32 deg f.
If the vehicle is brought into a warm shop the ambient temperature will not update on a 2012 or older vehicle unless it sits with the key off for 2.5 hours.
On a 2013 or newer you can perform a Ambient temperature sensor reset and it will update the temperature and allow you to run the test
Great tip! We have had this same issue with ambient temp with AC issues also.