There are conflicting accounts out there about flushing the 6-speed automatics used on the V8 and 3.2 XC90's, and a photographed how-to seems to be lacking, so I figured I'd put one together since I just finished this procedure on my 2007 XC90 V8 with about 100k miles. Although this is not a required maintenance procedure according to the owner's manual, I think most would agree that flushing the fluid every 20-30k miles is a wise decision. Note that there may be other methods of performing the flush (such as using a BG machine or draining the oil cooler and/or transmission first). I make no claims that this is THE way to go about the process, but this is what worked for me. Obviously, if you choose to follow what I did, you are accepting all risk for yourself and your vehicle.
That said, here's what you'll need:
12-14 quarts ATF (genuine Volvo, Mobil 3309, or Toyota T-IV--see discussions elsewhere for info on these and other options, e.g. Redline)
T-55 torx bit
T-25 torx driver
3-4 empty gallon milk jugs, marked at 2-quart intervals
Shop towels--you'll have some spillage
Trans cooler line seals/clip (ipd clip and o-rings)
Trans flush hose (ipd kit here w/ 3/4" OD hose)
(NOTE: if you buy the ipd trans flush kit, it comes with the green clip and 2 o-rings already)
Total time required: about 1 hour or less
Start by driving your vehicle until the transmission fluid is warm. In my opinion it does not need to be at full operating temperature, as this will be more likely dangerous and could throw off volume measurements of the old (hot) fluid vs the new (cold) fluid.
Park on a level surface, firmly apply the parking brake.
Open the hood and pull off the black plastic cover over the air filter box (2-3 clips hold it on), which should leave you with this:
Optional: remove the 2 screws holding the cold air duct to the radiator support (8mm socket) and remove the duct (for better access to the trans line, which you'll need later on).
At this point you need to access the transmission fill plug, which is located on the top of the transmission, below the airbox. There are multiple ways to access this. I decided to loosen the 5 T-25 torx screws that secure the upper and lower halves of the airbox (the screws you loosen to change the filter--visible as already loosened in the photo above), then I removed the lower half of the airbox--including the filter--from the engine bay. It's held on by one plastic nut along the fender, which just pops on and off. You'll need to start and stop the engine during the flush, so I didn't want to bother with disconnecting any electronics such as the MAF. I ended up running the engine without the air filter during the flush, but you're talking about a cumulative run time of less than 5 minutes, so I wasn't worried. I suppose if you live in a dusty environment, you might want to try a different procedure.
Once you have access under the airbox, identify the fill plug and use your T-55 bit to remove it:
Once the plug has been removed, set it aside and snake your transmission funnel down into the opening. Make sure whatever you have left of the airbox (e.g. the top half) is reasonably secure (reconnect any electrical connections you might have unclipped).
With the funnel now in place, turn your attention to the transmission fluid lines at the oil cooler (driver's side of the radiator). You're looking for the upper connection, as seen here (note that the retaining clip on mine had already disintegrated--I was glad I already had a replacement on hand):
Depress both sides of the clip to remove the line from the oil cooler--no tools are needed (though I had to use a small screwdriver on mine, since the clip was partially broken). As you pull the line out of the cooler, some fluid will dribble out, so be prepared with your shop towels and possibly a catch pan under the radiator. This is what you're removing:
Once you've removed the transmission line, you now want to insert your plastic hose. I used the 3/4" OD hose from an old ipd flush kit that I bought 7 or 8 years ago for my 850 Turbo. On that car, the in and out lines of the cooler were flip flopped, so the hose went over the male end of the line going into the top of the cooler. On P2 cars, however, I've found that you can insert the hose into the female port of the cooler output, which is the upper connection on these cars (where you just removed the cooler line). I don't think the ipd kit is technically designed for this, but I've found that it works perfectly on both my 2001 S60 T5 and my 2007 XC90 V8. I suppose you could add some tape to secure the hose (you certainly wouldn't want it to come out during the flush), but that's never been a problem for me. Another option would be to remove the lower line at the cooler (the input) and connect the hose to the male end of that line. However, I think you'd want to be prepared to catch all the fluid that would then come out of the cooler (and you would still need a way to flush the cooler itself). In any event, on the XC90 the fluid goes into the cooler at the bottom and out at the top, so plan your strategy accordingly, even if you're just going out and buying your own hose.
Here's my setup:
Route the hose into one of your milk jugs:
Begin flushing! Start the engine (trans in P) and fluid will begin being pumped out through the hose, into the milk jug. In my experience, it takes about 20-30 seconds to pump out two quarts. Don't rev the engine. I like to hop in the car, apply the brake, and move the shifter through P, R, N, and D, but I'm not even sure if that's helpful. What is helpful is to have an assistant watch the jug from outside the car and tell you when you've reached the 2-quart mark. At that point, shut off the engine and add two quarts of fresh ATF through your funnel (note how black the fluid is that's sitting in the hose--bottom left of the photo--that's why we've got to flush these bad boys!):
Repeat this process, two quarts at a time (changing milk jugs as needed), until you've used all 12 quarts or more of your fresh ATF. Remove your hose from the cooler (be prepared--some fluid may spill when you do so) and insert the line from the trans, having replaced the o-rings and the clip. Remove your funnel and replace the fill plug, then reattach the airbox, airbox cover, and the cold air duct. You're done! Just remember to properly recycle the old fluid.
Optional: Confirm Fluid Level
If you're certain you're replaced the exact amount of fluid that you extracted from the transmission, you can probably get away without checking the fluid level (which is unique because there's no dipstick). If you think you might have miscalculated on the fluid, put in a little extra before refitting the fill plug. The procedure for checking/setting the fluid level involves bringing the fluid to a specific temp (50-60 C I think), which you might need a DICE to monitor. Then you open the smaller plug within the drain plug (unsure on size) and let fluid run out until it just dribbles. If the temp is in range, you should be right on target. If no fluid comes out when you open the level plug, you need to add more.
Optional: Reset Trans Fluid Counter
If you have a DICE unit, you may also choose to reset the computer's transmission fluid counter back to zero. I'm not sure how to do this or what it actually affects, but some might find this step profitable.
Happy flushing! Comments and corrections welcome.