Problem with Ford Focus trip computer?

I've just noticed that the 'miles remaining before you run out of fuel' part of the trip computer on my 2003 Focus 2.0 Ghia is not displaying anything. All of the other readings (temp., average consumption, etc.) are working fine.
Could this be a fuse issue, or is it more likely to be a faulty component in the fuel tank where (I assume) the reading is taken?