# Central Locking Unit acting weird, re-setting codes?



## d3e786 (Nov 28, 2009)

This is a story about my central locking control unit acting weird, re-setting its codes, and generally behaving badly.

I apologize in advance for the length of this post but I find that without the details there is no hope of finding the correct solution.

I purchased my TT about 6 months ago (details in signature). Good deal, high miles (nearly 200K) but I'm OK with that as I am pretty handy with wrench, soldering iron, and laptop. (I used to own a Corvette, nothing scares me now!)

Everything worked fine. Did some work needed due to miles (new front end, struts, vacuum lines, repaired back window coming loose at corners, stuff like that).

One thing that was broken when I bought this car was the vinyl "rain gutter" located where the rag top meets the car deck. It's clear to me that this is designed to catch any water which will leak through the "seal" between the top and the deck when the top is up, and channel that water over to the door posts where it can drain.

I have no idea how long this was torn (the glue holding the vinyl to the rear deck had failed) but I was able to fix it following the advice of another TT owner (thanks for the help).

Of course, with that rain gutter torn any water getting between the top and the deck seal will run right onto the carpet deck behind the seats. I include this information as it may be relevant to the problem.

We now get into the fall season with some rain and one day I can't unlock the doors with the key fob. Change the batteries, no luck. Pull out the manual and perform the key re-synch. No luck. Everything works manually, just no remote.

So I figure my fob is dead and head down to the dealer for a new fob. Nice technician performs all the same procedures I just did, with same results. Gets new fob and does it again, still no luck. Tells me he will have to pull it into the shop, hook it to the computer, and see what is going on. Forty minutes later he comes back and tells me that the new fob works but that my car has other problems. I point out that my car had no other problems before I brought it to him. So he and I go out to the car and, yes, the new fob will unlock and lock the car, but now the horn will not sound and the lights will not blink. Even the manual lock button will not work. The interior lights are dead.

I'm pissed.

I go back inside and talk to the Service Manager who tells me that my central control unit is dead and will need to be replaced. I point out that none of this was a problem until I let them work on my car. General unpleasantness develops. He tells me that the only cure is to have them replace the central control unit. I inquire as to what that will entail. He tells me that the unit is located under the carpet under the drivers seat. He will have to pull the seat, trim, and carpet to replace the unit. I ask if I can just buy the unit and install it myself. He tells me that the unit must be programmed to fit my car and once programmed it can never be re-programmed. So if they mess it up, they will replace it free but if I mess it up then I'm out that unit and still have to buy another. This smells a lot like a scare tactic to me so I decide to "think about it". He tells me to hurry because what happens is that the water which got into the floor and ruined the unit (his story) will make it fail and then I won't be able to open the doors at all. I go home and start learning about the central control unit.

Of course, I find that the unit is located under a little hatch in the rear deck behind the passenger seat and that it can be accessed by vagcom and programmed to my hearts content.

So I get vagcom and my laptop and ask the central control unit how it feels. It replies with all zeros. The coding has been wiped, even the shop code is zeros. So I locate some coding data from a TT forum (thanks again to all TT forums) and enter a code and shop number.

Presto! Everything starts to work. I force the CCU to recognize my new key fob and presto, it works now, too. Everything is as it should be. So I start to wonder about my old key fob. I run the adaptation again and presto, the old key fob works fine.

Everything works fine and perfect for several days until I push the center console button to turn off the interior sensor, lock the car, and go shopping. Upon my return, the fob will not open the doors. Everything else still works right, but no remote.

So I hook up the vagcom again and the CCU is back to all zeros! Weird, since everything was still actually working. Anyway, I re-program the CCU and, presto, everything works again including the remote.

For a couple of days, at least. Then I turned off the interior sensor (gets false alarms if anything loud goes near or the wind is blowing), and when I came back, no remote again.

Looked at the CCU and the numbers had changed from what I had programmed, like it had re-programmed itself. Weird.

This has happened a couple of times now. Mostly the CCU is back to zeros. Sometimes it still has the code but has "forgotten" the remotes.

So the questions: How can the central console button be messing up the coding? Is the CCU water damaged from the failed rain gutter mentioned earlier? Is replacement the only hope? And what is the original code for my car? (that last one is not as important since I have codes which seem to work, but I would like to know how it was originally coded).

Also, has anyone decoded the bit map for the functions controlled by the CCU?

I've looked at the CCU with flashlight and mirror and I don't see any signs of water damage or water marks in the dust. I guess I could pull it out and open it up and see what is inside.

Details:
Part number on CCU: 8N7962267A
Original coding: unknown
Coding which is working: 15919
Code to which CCU re-set itself: 32767 or all zeros most of the time
Car details: see signature

Footnote: I found the following information on a website in Denmark. Google translated most of it into English, but there are a few words which did not go through. Can anyone help with these words and does anyone know if this is accurate:

(Locks) 
Server Coding 
[35 - locks] -> 
[07 - Coding] -> 
Coding Value (example).: 04142 
Default Encoding is 00000th 
 +00001 = Bagklapoplåsning 
+00002 = Acknowledgment alarm (blink) 
+00004 = Security locks Ning (SZV) 
+00008 = Burglar alarm (DWA) is activated 
+00016 = Semi-automatic hood 
+00032 = Autolåsning (lockdown from 15 km / h) 
+00064 = Comfort Function via Remote 
+00128 = Right-hand drive 
+00256 = Hatch Logic (DWA) 
+00512 = Acknowledgment remote locking (Blink) 
+01024 = Acknowledgment DWA horns active (short tone) 
+02048 = Dør-/elruderlogik (USA) 
+04096 = Acknowledgment remote opening (Blink) 
+08192 = Remote control activated

Thanks in advance if you have read all this and special thanks if you can shed any light on this rather peculiar computer/electronics problem.


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## d3e786 (Nov 28, 2009)

Several views but no replies. I'm bouncing this back up to see if anyone can give me some insight into this problem. This forum has been very helpful to me with other problems on my TT, so I am hopeful someone can offer at least a starting point to help me troubleshoot this problem. Thanks,
Jeff L.


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## stevebeechTA (May 16, 2009)

This is way over my head mate you have done well to get as far as you have. I am sure someone will be along to give you some advice.

Good luck, Steve


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## Wak (May 6, 2002)

For a TT Roadster LHD
Basic encoding for central locking (CL) without anti-theft alarm (ATW)
04688

Basic encoding for central locking (CL) with anti-theft alarm (ATW)
04698

You may want to try one of these first and see how you get on, I'm not sure where the Leading 1 is coming from in your coding but perhaps thats confusing things.

Try this out first and then if it works we can look at enabling features.


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## d3e786 (Nov 28, 2009)

OK, tried both of the base codes listed but neither one would be "accepted" by the central locking unit. After much much reading in many tt forums, I found what I believe to be the actual base code for our USA roadster convertable: 15900. That code seemed to work. Weird thing is that it took several "write" attempts before it would "stay" in the controlers memory. I also cleared out all of the stored key fob data using the procedure listed on RossTech and then tried to input my two key fobs. Only one would "take" into the memory. It didn't matter which one, but the second key fob would be ignored. Also, after the key fob was "stored" into memory, when the controller was "read" with vagcom it would show that no keys were stored. However, my one key fob does work, all functions ok. So, am I back to needing to replace the central locking "brain" in the near future or what? I find it very strange that it takes several tries to write a value into the controller, and then it seems to "forget" the stored keys (even though they still work). Any ideas?


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## jmsait19 (Aug 2, 2012)

Hi Jeff,

Don't know if you'll see this... But your post describes almost word for word the problem I'm seeming to have... Though mine has gone from "fob not working" to "fob not working, windows stay indexed down, top won't go open, alarm won't sound".

I believe, perhaps falsely, that these problems are stemming from the same place. I don't have vagcom to play with on my own, but I know someone who does.

Did some re-coding seem to solve it? Were you in need of a Central Locking Unit sooner rather than later?

Thanks for any help you may be able to provide.

-jason


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## cctech (Sep 16, 2017)

Hi guys 
is there a link between the chassis number and the CCU ? only reason i ask is i have a faulty one! and am now looking for a replacement, but all the ones with the same part number on as mine are £200+ but all the others are less than half that ? dose that mean i have a rare one?
thanks

cctech newby


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## black9146 (Jul 3, 2014)

Roadster units start with 8n7, coupes are 8n8. Roadster units are around £200 while Coupe units vary from £40 - £70.


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## gerontius (Aug 27, 2016)

black9146 said:


> Roadster units start with 8n7, coupes are 8n8. Roadster units are around £200 while Coupe units vary from £40 - £70.


That'll be because the Roadster units suffer from water ingress leading to strong demand for good used ones, whereas the coupe doesn't get the same issue (usually).


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## black9146 (Jul 3, 2014)

And there's less Roadsters compared to Coupe's


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## brianmcc51 (Oct 4, 2014)

I thought the key count was the number of keys registered to the immobiliser and not the number of remote fobs. I say this as the plastic valet key counts as one in the key count but clearly has no remote. The number of keys and remotes registered can be different.Please correct if i am wrong


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## Davetheconfused (Jul 7, 2015)

I'd guess, and it is only a guess as it's all a bit above my head, that it's keys to immobiliser because the keys have a chip of some sort to communicate to the car that its ok to disarm the immobiliser circuit? Leaving the central locking to maybe have a separate count of remote fobs coded to it? Although they are linked the remote unlocking and immobiliser disarming are technically two separate circuits ? If I'm wrong please correct me. 
The OPs problem sounded like a nightmare, and to me with my limited knowledge/experience may have been water ingress, but if not water ingress, sounded like either a power surge caused by a short or an earth fault. I'd have started looking around the centre console lock button, and considered any after market electrical items and where power had been picked up from to power them. I had some strange initial results when I tried to pick up power from the interior light contacts for a dash cam that I put down to me confusing the cars electronics by pulling the wrong current from one area and somehow feeding it into another circuit.
Sorry for the wall of text, as always I'm just throwing ideas around in the (quite possibly misguided, but genuine hope) that it might just trigger someone whos at the end of their tether with a problem into a eureka moment when they try something and solve a problem.


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