How do you remove the rear speakers located on a 2001 Nissan Altima?
I can't speak for a 2001, but on my 1998 I removed them through the trunk. Pretty quick and easy that way, just a few screws in each.
The 2001 Altima GXE Special Edition The way that I had to go about accessing the rear speaker housing was through the back seats.
I actually am going to be replacing mine tomorrow, and taking a tutorial video on how to replace them. watch youtube.com/ohnoesitsroy for the video to be uploaded in the next few days.
Try to use the Nissan speaker adapters plugs so you don't need to cut wires and mess up the electric system, you can get those from eBay or amazon.
It would be nice to know the year of your Nissan Altima. For Nissan 2000 Altima GXE the air filter is located right next to the battery. Just push off the 4 clips that hold the top of the filter housing and pull the top off just enough to remove/replace the air filter. Close it and and pull the clips back on.
For the 2002 - 2006 Nissan Altima, the ECM and TCM are both located under the dashboard, behind the glove box. You must remove the glovebox to access these modules. Remember that any yellow wires or connectors are for the air bags. You should probably refer to a service manual before accessing anything electrical/electronic.