When you say brake pedal sensor, do you mean the switch that is at the top end of the pedal that operates the brake lights??

If so it is easy to change just done mine, took about 5 mins. Just put the seat right back get in the floor and look up at the top of the brake pedal, the is a plug to take off and the switch is held in place by a clip take it out put the new one in and put the electrical plug back on. Job done.

Iirc the new switch was about 15 quid from the dealer and it was a dealer only part.

dave