Remove wheel you will then need a 5mm allen key to undo the sensor bolt by going through 1 of the wheel bolt holes slide out sensor towards front of vehicle unclip wiring undo the connector then clean up the area where sensor sits as there will be a large build up of rust which has to be removed to get the correct airgap when fitting the new sensor which is about 2mm between sensor and the hub ring
Peugeot master technician, September 2008