DIAGNOSTIC AND RECIRCULATION CONTROL SYSTEMS AND METHODS

A vehicle system includes: a heating, ventilation, and air conditioning (HVAC) system including: a passenger cabin air filter; and a blower configured to draw air through the passenger cabin air filter and blow air into a passenger cabin of a vehicle; an olfaction sensor configured to measure an amount of a chemical in air in a duct of the HVAC system downstream of the passenger cabin air filter; and a filter module configured to determine and indicate whether to replace the passenger cabin air filter based on the amount of the chemical in the air measured by the olfaction sensor.