abs light on, on dash

[RobMorgan]

whilst trying to get my abs sensor out the other day, i was turning it from left to right in the hub to loosen it
it finally came a bit loose, but i still couldnt get it out, so i unplugged the other end of the wire

when i have put it all back together again, the abs light has come on, on the dash

would it be because i pulled it out a bit, and needs to be pushed all the way in?
or
is it more than likely broken?

will it fail its MOT with the abs light on?
audi want £127 (about $250) for a new 1