An exhaust system includes an exhaust pipe and a heat insulating cover surrounding an outer surface of the exhaust pipe. The cover includes a planar section defining a surface area. An inner surface of the planar section is spaced from the outer surface to define a gap there between. A separate reinforcement is mounted to the planar section. A mounting boss provided in the gap is in direct contact with the inner surface. An exhaust constituent sensor is mounted to the exhaust pipe. A distal end portion of the sensor is received in the mounting boss and projects through an opening in the outer surface and into an exhaust passage. The direct contact of the mounting boss with the inner surface forms a mechanical seal preventing high temperature air from around the exhaust pipe from flowing toward a proximal end portion of the sensor.