I was changing oil and differential fluid and was thinking about doing transmission too. I found the drain plug but couldn't find the fill plug. Can anyone in TL land help me out?

 

If you have an automatic I'm pretty sure you fill from the tranny dip stick.

 

See below link: Item 12.
CASE, TRANSMISSION/AT TRANSMISSION CASE (5AT) for 2009 Acura TL

Either a 17 or 19mm socket with long extension(s). Will take a great deal of torque to open the first time.

 

Oh what the hell lol. My mech's been doing it through the dipstick hole.

 

Your fill plug is on top of the transmission 17mm and a crush washer you should get 4 qts of Acura transmission fluid and a new crush washer at the dealership. Your going to need a long extension and a ratchet you might need a piece of pipe for your ratchet for leverage when taking the fill plug off dont worry it will come off . When you replace the fill plug use a little anti-seize on the threads of the fill plug so next time you change fluid the plug will come out easy.....word.