The invention relates to a valve designed to seal a port (36) in the structure (10) of a motor vehicle exhaust line muffler (1). The valve (38) includes a plug (44) which can be connected to the structure (10) and occupy a position in which the aforementioned port (36) is sealed. The plug (44) can be raised from said sealing position by means of bending. The plug (44) also includes a sealing plate(54) which can seal the port (36) and at least one connecting plate (56) which can connect the sealing plate (54) and the structure (10), said sealing plate (54) and connecting plate(s) (56) having different thicknesses and/or being made from materials with different mechanical properties.