It looks like a vac line should be connected here, but I'm not sure. I don't know what it would do if it were connected anyway as it seems that the vac line coming into the switch and the line coming out to the EGR should be all that is needed. I get a Check engine light from time to time, I've never pulled the code, but I was just looking things over looking for something obvious. BTW - when pulling codes, do you have to leave the truck running once it throws the code in ordr to check it? Every time I get the ses light and kill the engine, it goes away by the time I restart it and stays off for quite some time.