Unable to Read Your OBD-II Codes?

If you are resourceful enough to utilize your car's On Board Diagnostic (OBD) system, you're way ahead of the game. (Don't forget you can have your codes scanned free at any AutoZone). If you've plugged into your car's diagnostic port and aren't reading anything at all, you might think that your OBD-II brain has fried, but don't declare it dead yet.
On many cars, the ECM (that's the electronic brain) is on the same fuse circuit as other electrics like the cigarette lighter/accessory port. The lighter is prone to blow fuses on some vehicles, and if there's no juice going to the ECM, it can't tell you what's wrong.

If you're getting nothing, check the fuse!

Article Source: http://autorepair.about.com/od/obdcodedatabase/qt/obd_fuse.htm