I decided that I will replace the gear oil in the forward and rear differentials, and also the center diff/transfer case this year. I want to tackle the forward and rear diff's first as these appear to be easier than the center diff, but I am not finding a complete procedure in the workshop manual for the "0BD" rear diff. It only addresses a fluid level check for 0BC & 0BD versions of the rear diff. It does include complete replace/refill instructions for the 0BE and 0BF versions. To be honest, I am not even sure which diff I have. I looked at my vehicle ID label and it does not appear to cover codes for the differentials. So, my first question is how do I identify the version of all 3 differentials?
As for the refill procedure, I just wanted to determine if it was necessary to run the vehicle and warm up the diffs before doing a final top off of fluid? It looks like the answer may be "no" and to just take your time filling it up to allow the gear oil to disperse.
Lastly, is there a consensus on what gear oil should be used for refilling the center diff (transfer case)? I came across a discussion where it was suggested that the expensive gear oil (with friction modifier) should not be used for a simple refill and is only necessary when replacing or repairing the center diff because the friction modifier does not need to be replenished. If true, the same gear oil for the forward and rear diffs can be used for the center diff.
Note: I did finally download the VIN specific workshop manual for my 2014. Here is the section that covers the rear diff:

 

The rear diff code is before the trans code on the vehicle identification sticker.
engine <space> diff / trans
The code value is not the same as the type value.
type 0BE/0BF are the sport diffs, you're not going to have those.
type 0BC/0BD are the standard diffs, the 0BD is a lower power handling economy diff used only with the ZF transmission. 0BD has the drain plug at the bottom of the rear face; 0BC has cooling fins and the drain plug on the bottom.
ZF8+CPM, you probably have type 0BD code KHR (0BD500043G).

The front and rear, you do the fill at room temp. So if the car has been sitting outside in overnight cold and is 50°C, you need to let it warm through to 70°C.
No need to do any spin and top off, but it does say to fill it slowly to allow settling. Maybe front diff only, but I recall "fill it over the course of 5 minutes".

The Torsen center diff is not the same kind of gear design as a front or rear diff. The workshop manuals do not differentiate the center diff fluid for repair vs replace. It ain't cheap, but either use it, or leave the diff alone, is my opinion.

 

Thanks SMac, great information!
I do have the "KHR" code for the Diff and the "PRW" code for the Trans. Engine codes is "CPMB". I would never have guessed that the codes following CPMB were the Diff and Trans codes because my warranty booklet description for this line of codes is: "Engine Code / Engine No.".

I did come across the "fill over 5 minutes" instructions for the front differential and I extrapolated that doing the same for the rear diff would be a good practice. So I will plan to do this work during the warm summer months (Wisconsin) and with the car on a level/flat surface. Do you know why there are no fill instructions for the 0BC and 0BD diffs? Is it a case of Audi specifying the fluid as "lifetime"?

You read my mind on the center diff. Better to leave "as is" rather than put the wrong fluid in. I will see if I can find that discussion I referenced and add a link if I do find it. So far, I have not been able to find any Audi documents that specify the plain 75W90 gear oil (G052145S2) for a simple refill of the center diff/transfer case. I have found two Audi fluid capacity guides that specify the $120/liter axle oil (G055145A2) without distinction. Here is the 2014 guide that I just downloaded from erWin:

 

It appears someone was given the task to consolidate the separate rear diff manuals into one. They copied into the 0BE/0BF doc the level check process for the 0BC and 0BD. But there's no drain/fill process for the 0BC/0BD because there was none in the original separate manuals either. I guess they figured it was simple enough. The manual details the fill/inspect plugs, their torque specs, and how to know when the fluid is at proper level (checking fluid level). But ignores the drain plugs entirely. As they are the same p/n as the fill plug, I just used the same torque spec for both. The 0BC torque spec (30 Nm) and the 0BD torque spec (45 Nm) are not the same.

 

Did you re-use the original plugs? The manual suggests to "replace" the plugs for OBE & OBF. I'm guessing that re-using should be fine and I really don't want to pay almost $20 for a new plug.

 

The plugs for 0BC and 0BD are not "replace if removed". 0BE and 0BF are the sport diff, whole different world, don't bother looking for any info cross between the the sport diff pair and the standard diff pair.

Not sure if it'll be the same on the Q5, but for the 0BD in the A4, the drain plug is located such that you can't get a normal torque wrench with bit on it. I had to use a hex key and then a torque wrench with crowfoot, or something like that, to torque it correctly.

 

Thanks for the heads up on the torque wrench. I will take a good look at the rear and front diffs before ordering the fluid. I did purchase a couple of exchangeable head torque wrenches last year and I might be able to use one to grip a hex bit in a tight space.

 

Oh, nice. Which ones did you go with? I'm still making use of my Craftsman click style ratchet heads, and a Tekton for the 1/4" size. Looked at interchangeable head ones; Audi toolset is based on those. And for a number of instances in the procedures, the special tool is a head for an interchangeable. Crows feet sets are ok, though expensive for what they are, but still leave something to be desired. But, for the cost of a whole new wrench set, just never did it.

 

Here is what I purchased last year, including a larger with a fixed crescent style head:
Small torque wrench: Mid-size torque wrench: Large Crescent head: I paid only $70 for the big crescent head wrench, and now I see it is at $200. I guess that is Bidenomics in action.
The heads on the small wrench are interchangeable with the mid-size wrench. It was not easy finding a reasonably priced torque wrench with the interchangeable heads. Both work well.