After just over a year of ownership and about 20,500 miles, my MID gave me a service code of A16, which means tire rotation, oil change and the 6 means rear-differential fluid change (note this would only apply to AWD vehicles, obviously). 20K is pretty quick for a diff change, I thought, but I figured this was a break-in maintenance item to clear out the metal bits that are created during break-in. All-in-all, this will be either a very easy thing or a PITA, which will depend on what device you have to pump the oil into the diff....
This procedure is essentially the same as it is for most (all?) rear differentials I've seen. There is a drain plug at the bottom of the differential and a filler plug about half way up case. You just drain out the old and fill it up until the fluid starts to leak out the filler hole. Simple, right?
1) Get your stuff:
* 3/8" socket wrench (no sockets, though)
* Two quarts of Acura All-Wheel Drive Fluid (DPSF), which ran about $9/qt at my dealer -- the manual gives the oil change capacity as 1.3 qt.
* New crush washers for both the filler and drain plugs (they are different sizes).
* Oil drain pan
* Torque wrench... theoretically. I couldn't fit mine in there, so didn't use it.
* Fluid transfer pump or some means of pumping the oil from the bottle to the diff case -- you won't be able to pour it.
Foreward: I found it easier to access the drain from the rear of the car, and the filler from the drivers side. Theoretically, the oil will flow better if the car is warm. That said, you'll be crawling around right by the hot exhaust, so I figured discretion is the better part of valor and let it cool down. The fluid is thin like water, so it seemed to flow fine anyway.
1) Put your oil pan under the differential case. The diff case, if you don't know is between the rear axles. You'll see the transfer shaft coming from the front axle.
2) IMPORTANT! First thing you need to do is make sure you can get the filler plug out. You will be very unhappy if you drain the oil out and then discover you can't get more oil back in. The filler plug is on the driver side of the differential, ahead of the axle, with a little lip/shelf beneath the plug and the case is conveniently marked "DPSF". The filler plug has a square 3/8" hole you can remove by using your 3/8" ratchet shaft. It shouldn't take too much effort once you break the seal of the crush washer. When I first opened this plug when hot, fluid started to drain, so have the pan ready.
3) IMPORTANT! Make sure you have a means to get the fluid into the filler hole. I could find no way to pour the DPSF fluid into the diff -- you'll either need a funnel with a loooooong tube or a transfer pump. I could not find my bloody pump and had to pitstop at WalMart where I picked up a $3.50 siphon pump. I don't recommend using this, as it is insanely slow and incredibly messy.
4) Make sure your pan is positioned correctly and remove the drain plug. It's located on the passenger side at the bottom rear of the diff. This is also a square-hole plug where you simply use your 3/8" ratchet's bare shaft. You'll see the diff case is pretty flat, so I jacked up the driver-front of the car and sure enough, a bunch more fluid came out. Lower the car when the flow stops. For me, the fluid looked brand-freakin-new after 20,000 miles. BUT the key thing is to look at the magnetic drain plug -- it was covered with metal bits. THAT is why you're changing the fluid now... break-in.
5) Once the fluid is all out, clean the magnetic drain plug thoroughly before installing. Use your new crush washer and tighten up the plug to 35 ft-lbs (note - I couldn't get a torque wrench on there so I tightened just until the crush washer deformed. No need to over-tighten.)
6) Catch pan still in place, move back over to the filler hole and pump in enough DPSF fluid until it starts to overflow out the filler hole. In my case, using a siphon pump, I held the bottle as high as possible near the passenger rear door handle and waited... and waited... and waited... Once the fluid starts to overflow and you're satisfied it's nice and full (1.3 qts), install the filler plug with the new crush washer and torque to 35 ft-lbs (again, my torque wrench did not fit).
6) Wipe things up nice and tidy so you can see if any leaks develop later on.
7) Drink a beer.
This should be a pretty easy/straight-forward maintenance task if you've got a pump that works OK. Pretty similar to an oil change. The key thing is to make sure you can get the new fluid in before you take the old fluid out.
Have no fear!