Recently every time my Sierra goes into overdrive it triggers the check engine light to come on. I have plugged it into the computer at my familys garage and it's coming up evap valve. I took the valve off and blew it out with an air hose and reinstalled it and reset the code. The light stayed off for a few days until today driving back from work I passed someone and as soon as the overdrive kicked in the light came on. I am going to plug it back into the computer and see what it reads. I'm just curious if anyone else has had this issue.