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Here is some good news if, like me, your daily driver is a 2000 Audi A6 Quattro 4.2 V8 and you realize that its transmission control module is critical to the forward gears working correctly. Without a healthy transmission control module, the car will move forward only in 5th.

That module is located under the carpeting, under the front passenger footwell, inside a plastic case that’s not waterproof, so if that area gets drenched enough, you might be in the market for a replacement unit.

If, like me, you initially just searched for part number is 4B0927156 and found a unit, installed it and the car ignored it, you realize that those last two letters make all the difference.

I gradually learned that the part number of 4B0927156 was used for a slew of VW and Audi transmission control modules made right around the year 2000, with various one-letter or two-letter suffixes. I’ve found they are generally not interchangeable.

However, I wanted to make sure. So, today, I cycled more than half a dozen separate transmission control computers through my car. I found that the 4B0927156AJ unit (as allegedly used in the 2000 Audi A6 Quattro 2.7 Biturbo) doesn’t work in my car; the car ignores it. I found that the 4B0927156BH unit (as used in the 1998 Audi A8 Quattro 4.2 V8) doesn’t work in my car either; the car ignores that, too.

However, the 4B0927156CT unit (as used in the 2001 Audi A6 Quattro 4.2 V8) does indeed work just fine in my 2000 Audi A6 Quattro 4.2 V8 car.

A couple of years ago, I gave my mom a birthday present of a 2000 Audi A6 Quattro 4.2 V8 car. I borrowed her car for some more testing. To my surprise, in her car, the 4B0927156CT unit does NOT work; the car ignores it. Odd.

If you need a 4B0927156BS unit, then I can sell you a good, guaranteed one, but it`s not cheap, and so now you know that if instead you can find a cheap, good 4B0927156CT unit somewhere, that might just work for you.

If you specifically need a 4B0927156CT unit, I sell those too. Not cheap, either.

I like to test each of these 4B0927156BS and 4B0927156CT transmission control modules I sell before I pack it. If you like, you can ask me to make a video-recording of that individual part working while someone drives the car with it installed.