Have you checked to see if the "fault" is actually the car testing the circuit to make sure all is well ?
It could be the sensor being given a signal and the signal being sent back to cofirm it is working correctly.
Ask a local dealer or independant garage if they can shed some light on it for you.
As long as the message does not stay on, and the car drives ok, then i would say you have little to worry about.
1 litre Zetec Turbo petrol 74Kw / 100 Ps. as in my avatar.