DCT Transmission from Hell

[Bigb76]

Hello,

Posting on here to document and get some questions about my DCT.

I bought a 2011 e93 M3 with 65k miles as a project. I knew the transmission was faulty in some way and would need fixed. Plugged in a Foxwell scanner and it was unable to communicate with the transmission, wouldn't even connect to the module. I'm not super experienced with INPA and ISTA, but tried that route and could not reach it either.

(I should add that when I got the car, the Vin on the DME did not match the car, I am also working to rewrite the vin on the DME. So would a mismatched vin not allow the transmission to communicate? I would think it doesn't matter.)

Did a lot of reading on forums and figured it could be wiring harness related. Did some looking and nothing was out of the ordinary from what I could tell (not brittle, connections seemed okay). Then I figured it could be the mechatronics unit. I wanted to check the fluid level in the transmission, so I opened the fill plug... nothing. I went to crack open the drain plug and what came out was about 2 liters of "egg-nog" (attachment 1)

After seeing this, I figured the only place coolant could get in was the intercooler on top of the transmission. I knew the whole DCT had to come out, so I started that process and eventually got it out. I opened up the mechatronics side panel and found more egg-nog fluid and a bunch of dirty sludge. (attachment 2).

I don't know how water could get in the transmission (besides a broken intercooler), and from what I know and can tell about the rest of the car, has not been in a flood.

Has anyone seen anything like this? I would guess that the water that got in the transmission fried the mechatronics unit and then it wasn't able to communicate with the vehicle or any scanners.

I have ordered a used transmission with 44k miles and a bunch of fluid, gaskets, O rings, bolts, etc to make sure it doesn't leak, as I've seen that be a common problem on these. Still waiting on the arrival of the transmission, so fingers crossed I can plug it in and it works.

I can provide some of the codes I got as well for the car when I plugged a scan tool into it.

Also wondering if the two DC-DC torque converter modules next to the DME (part numbers 61429253208 and 61429253209) would cause any of this if they were toast or mismatched in the wiring harness?

Will keep updating as this progresses. In the meantime, any ideas for moving forward once I get the transmission in?

[Redd]

DCT uses an oil-air cooler so there should not be an easy way for water/coolant to enter the gearbox. My only thought is someone messed up during a service and filled the wrong fluid.

I'm no DCT expert but if that sludge is in the gearbox, it's everywhere. God only knows what damage it has done. You're probably wasting your time trying to troubleshoot it. Just put in the used transmission and call it a day.

[spammysammich]

The heat exchanger on top of the DCT is water/oil cooler, if that is damaged it could cause that mix.

https://www.fcpeuro.com/products/bmw...vD_BwE#fitment

[Redd]

Oh I was not aware there was a heat exchanger up there. Thanks for the clarification. Is it a common failure item?

[spammysammich]

Originally Posted by Redd

Oh I was not aware there was a heat exchanger up there. Thanks for the clarification. Is it a common failure item?

IF this is the main cause of this failure, this would be the first I've seen posted in 3 years of lurking here.

[Helmsman]

Originally Posted by Redd

Oh I was not aware there was a heat exchanger up there. Thanks for the clarification. Is it a common failure item?

Like Spammy, never read about it during my 10y, fortunately. Tend to agree on wrong fluid, where would water come in. Also cooler and lines need to be cleaned/replaced.

Btw this heat exchanger is feed by the aux pump and a reason for heat issues at low speed when the pump is broken.

[GORDON.M3]

Wild, this is the first time of been on the E9x M3 groups for the past 10+ years that I have heard of a heat exchanger core failure that caused DCT fluid to be contaminated.

[Redd]

Originally Posted by Helmsman

Btw this heat exchanger is feed by the aux pump and a reason for heat issues at low speed when the pump is broken.

You mean the small aux pump behind and under the airbox? I thought that was for heater function only. Luckily I replaced mine when it started giving errors.

[spammysammich]

If I recall correctly that aux pump is in the coolant circuit along with that heat exchanger. I get an error from it now and then but nothing persistent and sometimes goes months without recurring. I might pick up a spare since they're easy to change, i see them for sale from Mporium every now and then.

[Helmsman]

Originally Posted by Redd

You mean the small aux pump behind and under the airbox? I thought that was for heater function only. Luckily I replaced mine when it started giving errors.

Thats the one, for both coupe heating (stationary) and the DCT coolant/fluid heat exchanger.

[Helmsman]

Originally Posted by spammysammich

If I recall correctly that aux pump is in the coolant circuit along with that heat exchanger. I get an error from it now and then but nothing persistent and sometimes goes months without recurring. I might pick up a spare since they're easy to change, i see them for sale from Mporium every now and then.

Same it was on/off for some time and eventually gave a code soon as assumingly turned on. No DCT heat code for a long time after I replaced the pump. Back again but different subject...

[Bigb76]

A little update on this, I've been MIA and got around to this late.

The used transmission came in and I got it in the car. The car now recognizes it's in park, so it confirms my suspicions the mechatronics unit was junk.

I went to fill it with fluid according to ISTA repair guide and went to start the car. However, now the engine will crank but not turn over, presumably due to the new transmission. Does anyone have any guidance on how to reflash either the DME or DKG, or how to change the vin numbers to match?

[Helmsman]

Originally Posted by Bigb76

A little update on this, I've been MIA and got around to this late.

The used transmission came in and I got it in the car. The car now recognizes it's in park, so it confirms my suspicions the mechatronics unit was junk.

I went to fill it with fluid according to ISTA repair guide and went to start the car. However, now the engine will crank but not turn over, presumably due to the new transmission. Does anyone have any guidance on how to reflash either the DME or DKG, or how to change the vin numbers to match?

Haven't checked myself yet but from what I've read Bimmergeeks Protool can change VIN when replacing modules. Whether the DCT is counted as such.
Edit: There are a few videos on YT worth searching for.