My "Service Engine Soon" light keeps coming on. The code is 1400 and no one seems to know what this is for...

I have already had the differental sensor, brake lights, gas cap, etc., replaced or checked and it continues to come on. No one seems to know what the code "1400" means. If anyone can tell me, so I can get this problem taken care of, that would be great. The car is a 2000 Mitsubisho Montero Sport. Thanks!