Some embodiments include a housing including a dielectric portion, a particulate matter (“PM”) sensor fixed inside the housing such that the exhaust streaming through an exhaust system passes near and in electrical isolation from the PM sensor, the PM sensor including a terminal couplable to a PM sensing circuit to produce a PM sensor indication associated with sensed PM and a fastener coupled to the housing and mountable to the exhaust system to dispose the housing into the exhaust system such that exhaust streaming through the exhaust system passes outside the dielectric portion of the housing.