A vehicular crash sensing system is provided wherein a bumper cap contacts a bumper. A chamber is at least partially fit into a side rail attached to the bumper, wherein the chamber is sealed by the bumper cap. The bumper cap and chamber together enclose a space containing a volume of air. A stop element limits movement of the chamber into the side rail. A pressure sensor detects an increased chamber air pressure during crushing of the chamber resulting from movement of the bumper with respect to the stop element.