Exposure gone haywire

After years of excellent results with this superb camera - the lens is unmatched as Andy Piper has reviewed, the digital innards are now faulty. As soon as I press the exposure button halfway I get an exposure reading of 1/4000 (not in fact available on this model!) whatever the light conditions and this (or something like it) is what the camera chooses when picture taken. Is this a serious fault costing much money to repair?