Well, first check for a blown fuse. I do not have the schematics here at home with me or I'd be able to tell you which fuse it is.
If it is not a fuse then you will need to pull the cover and see if you have power to the plug that connects the over-head temperature LED's. If no power, you'll have to go back wards to see where you lose it. If you do have power, then the gauge unit may have failed.
I doubt that the unit has failed. If so, it will be the first that I have heard of...