OBD Sensor cannot connect

I went to get my truck smogged and originally the check engine light was on so I disconnected the battery and went through the drive cycle and went back. The second time they said that their sensor could not connect to my OBD and suggested I change the cigarette lighter fuse. I replaced the fuse which was blown and returned but it still could not connect. What should I try next? I cannot find anything about which fuse controls the OBD in the manual.