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If you haven't changed the cabin filter in your CTS-V yet, you might be surprised at the build up! Recommended change is annually!
WIX Cabin Air Filters
High-efficiency cabin air filters for passenger cars, light trucks, heavy trucks, buses and off-highway vehicles. Trap & eliminate harmful microbes in the filter medium and reduce the opportunity for those microbes to be released into the air of vehicle occupants. Use PART NUMBER drop down to select filter.