I just bought a new cabin air filter at a local auto store for my 2003 4Runner. Cost me $28. I found instructions in the box on how to change it. It took me 10 minuets to do it. Toyota wants $58 to change it.
Its for installing an auxiliary audio device, like a CD changer or a satellite radio. You have to remove your radio to attach a device to it. There was no auxiliary input in the 2003 Toyota matrix and was not optional the first aux was for the 2006 matrix and up