Just before Christmas I lost power steering temporarily and the dealer fit me in that day to check it out (i'd actually lost ps one other time but didn't tell them about that until the next service). They found a faulty ground on the steering wheel angle sensor and they thought this may have been the cause of it (i actually lost power for a moment before i realised the ps had stopped working but thought it was the traction control kicking in because of my driving. The service tech asked me about it during the test drive which is when i realised it may have been related).