Amazingly enough most of the population have NO IDEA that they even have a cabin air filter, I once worked on a 2001 Tahoe. The early 800 series had cabin filters but were cost cut out after, I think 2003. The truck had very low air flow...pulled the filter out, which is under the dash and easy to reach, the thing was filthy and had so much junk sitting ON it that I pulled junk out of the duct work that backed up. Second story was a 2004 Toyota Solara - same thing low air flow with a clogged cabin filter. I tell people to READ the OWNERS manual and they would know all they need.