Vehicles equipped with an occupant detection sensor in the seat bottom utilize this device as part of a two-stage deployment airbag system. The 3 Series models feature an OC3 mat integrated into the seat cushion, which is replaced as a unit. To access the occupant detection sensor, first disable the detection mat from the restraint control module using a BMW factory scan tool or equivalent. Next, remove the passenger seat, followed by the seat control switches. Detach the fastener and seat cover clip panel, then remove the trim panel by prying the clip out of the seat cover on the right side. Unhook the seat bottom upholstery at the rear and pull it away from the seat frame, with assistance pushing down on the seat bottom cushion to facilitate this process. Completely pull out the cover welt from the seat frame and move the seat cover with cushion in the indicated direction, carefully feeding the bracing cloth through the gap in the backrest. Disconnect the harness connector for the occupant detection sensor and seat heating if applicable, then remove the seat cushion while detaching wire retainers. Installation follows the reverse order of removal, ensuring to enable the detection mat with the BMW factory scan tool or equivalent afterward.