Mud in my Veins
Join Date: Mar 2005
Location: San Diego, CA
Thanked 4 Times in 4 Posts
On your GM truck, the cigarette lighter fuse also powers your OBDII port. Check the fuse box for CIGAR fuse. If it's blown, swap it with the proper auto fuse. Even if it looks good, test it with an ohm meter, or simply exchange it with a good one. Sometimes this fuse gets overloaded with gizmos attached to the cigarette lighter and will blow. Your OBDII port should be good again once you resume power.
Test at home with your own OBDII scanner before taking it into the smog shop again.