# Rear window heating not working with new climate control uni



## jokskilove (Sep 10, 2013)

I put in a new used climate control panel today. All buttons seem to work, except for the rear window heating. The light is on while I press the button but turns off immediately when I release.

The old panel parts no. ended in AG, which is supposedly not compatible with the model year I have. The new one ends in AQ.

Anyone know if there is a coding I need to change, or anything else I could try. I didn't test the heated window on the old panel before swapping, but the most likely cause seems to be some coding.


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## MT-V6 (Jan 11, 2015)

The coding on mine (8J0 820 043 AG) is 1049606, but I'd need to check VCDS to know what that means

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## jokskilove (Sep 10, 2013)

Which part/area is that? (I'm not that familiar with VCDS - don't know if it's obvious to go looking for it)

Which year is your AG panel from?

Anyone out there have an AQ panel for comparison? (Mine's an 07, which was supposed to be with the AQ, but I got an AG fitted when I had heated seats retrofitted)

PS. What's the story with the AG panel? I've searched https://audi.7zap.com/ on different model years, but they all seem to deny its existence - two Audi dealerships say the same thing..


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## MT-V6 (Jan 11, 2015)

It's module 08 on VCDS. I got that from a saved scan but don't have the description of the coding to understand what it means

I assume it it the original one so would be a 2007 part (MY2008). It is also for heated seats

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## Hoggy (May 8, 2002)

Hi, I assume you have checked Fuse No.25 ?
Hoggy.


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## SwissJetPilot (Apr 27, 2014)

@ jokskilove - VCDS is a software program that uses a cable to connect to the OBD (On Board Diagnostics) to a laptop PC which allows one to access the vehicles computer. The OBD plug is located under the drivers front panel (it's the big purple plug under the dash, just above your right ankle for RHD).

This post will give you an idea of what can been seen on a PC using VCDS when accessing the OBD computer. In this case it's Module 09 for the Central Electronics. https://www.ttforum.co.uk/forum/viewtop ... &t=1837153









The Module 08 (outlined in green) being referred to my MT-V6 is for the Auto HVAC which is where you would go to look for the coding of the HVAC system.

When you use a VCDS and run an AutoScan to check for faults, you would see something like this for Address 08. You'll note line 5 is the "1049606" code MT-V6 is referring to -

_Address 08: Auto HVAC Labels: None
Part No SW: 8J0 820 043 S HW: 8J0 820 043 S
Component: J255 Klima 1 Zone 0060 
Revision: 00H07003 Serial number: 00000001035351
Coding: 1049606
Shop #: WSC 01236 785 00200
VCID: 366513C54195D1AE71B-8063
No fault code found._

The coding is how the car is configured and represents a combination of choices from a menu as shown here, where each digit represents a value from, in this case, the engine coding options for Module 01 Engine -









In this example "0150031" represents the following choices -

First digit is 0 (default)
Second digit is 1 which means "Manual Climate Control (Climatic)"
Third digit is 5 which is "without flexible Service Interval"
Fourth and fifth are 0 and 0 (default)
Sixth digit is 3 which is 1 + 2 [Brake Electronics (ABS) + Airbag]
Seventh digit is 1 for "5-Speed Manual Transmission"

In order to know how your Module 08 is coded, you would have to get into this feature to see the yellow "bubble" code options and combinations. The problem here is what's on your car may not be the same as what's coded on some else's car. But if we at least knew your code, we could probably figure it out.


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## tttony (Dec 21, 2014)

Is it just the light that goes out or is the screen not actually heating up?

The power to the screen is provided by a relay in position B5 on the Onboard Supply Control Unit under the dash panel. The switch controls that relay. It is possible that the relay is being energized but the indicator light on the switch is faulty.


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## jokskilove (Sep 10, 2013)

Thanks for the hints, guys.. I think the fuse might be a good place to start. I blew one when I installed my new seats. Maybe the neighbour got smoked as well..


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## jokskilove (Sep 10, 2013)

Nope, not the fuse.. Hoping for a misty morning tomorrow so I can test if it heats or not.


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## MT-V6 (Jan 11, 2015)

I had a look on VCDS today and there doesn't seem to be a labels file for the HVAC module. i had a google and similar scans also show no label file found, so I am unable to tell you what my coding means. All I know is that I haven't changed it, and that it has heated seats and the rear window demister works!


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## SwissJetPilot (Apr 27, 2014)

@ MT-V6 Check 09-Cent Electronics. It looks like the module for the rear heater is in there, not HVAC.

https://www.ttforum.co.uk/forum/viewtop ... &p=9004395


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## MT-V6 (Jan 11, 2015)

That's true, though if all that was replaced was the HVAC then the central electronics coding would be the same

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## SwissJetPilot (Apr 27, 2014)

Good point. Unless it requires an Adaptation after the replacement of the controller.


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## MT-V6 (Jan 11, 2015)

I didn't check adaptation, I'll look next time

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## SwissJetPilot (Apr 27, 2014)

No worries. I was thinking since the heater control unit changes the position of the HVAC vent flap servos, (similar to the roof flap servos on the Roadster) there may be an and adaptation required which might affect the rear defroster too.

*EDIT* - I would recommend downloading the Workshop Manual from the link in the KB for the reason noted below from Section 1.3 of the HVAC Repair Manual, Audi TT 2007, D3E80068107. Here's the pages that seem to be relevant to the removal/install of the control unit -


_If the Climatronic control module -J255- is supposed to be replaced, check the coding and adaptation before removing it using the "Replace Control Module" function, starting with Vehicle diagnosis, testing and information system -VAS5051B in the "Guided Fault Finding" function._


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## jokskilove (Sep 10, 2013)

Thanks for all the hints, guys! Doesn't quite seem to crack the code.

When I visited the dealer, some basic reset program was done (not sure if that's what you refer to as adaptation - bloody Danish lack of vocabulary).

I might have to plug in the old module, read the coding (and test the defroster), and then plug in the new one for comparison


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## MT-V6 (Jan 11, 2015)

Yes my first step, if not fuses, would be to test the old module out again

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## SwissJetPilot (Apr 27, 2014)

"Adaptation" is the how the vehicle's computer "knows" where things are. Let me explain -

In the case of the convertible top roof flaps, when they are replaced or refurbished, an Adaptation is performed with the VCDS so the vehicle knows where the flaps are in relationship to the top during the up/down operation so they con't crash into each other. Adaptation for the roof flaps establishes the maximum up and down positions of the flap servo based on a pre-defined (expected) voltage range since the servo is actually a potentiometer or voltage divider.

You can go to this post to see what a servo looks like inside. Both the roof flap servos and HVAC servos are similar in design and function -
https://www.ttforum.co.uk/forum/viewtop ... &t=1786641

The HVAC unit uses a number of servo motors to control the internal HVAC system vent flaps for heating and cooling control and air flow distribution, I'm guessing an Adaptation is necessary so the climate controller knows the open and closed positions of each servo. By establishing the maximum and minimum values, it can then correctly position the flaps for hot or cold and drivers and passengers air flow distribution.

This link will provide more details into the HVAC unit and related servo units -
https://www.ttforum.co.uk/forum/viewtop ... &t=1754442
.


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## MT-V6 (Jan 11, 2015)

However adaptation can sometimes also enable things as well as adjust values (eg durations). I can't think of an Audi that wouldn't have a heated rear screen so in this case it doesn't make sense, but it could potentially be something that could be enabled in this way. But there are no labels in VCDS :/

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## SwissJetPilot (Apr 27, 2014)

Yes, exactly. In the case of the climate control unit, the Adaptation might also run a check to ensure the rear window heater is present and verify the resistance of the circuit; e.g. no broken or open traces in the glass.


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## jokskilove (Sep 10, 2013)

It's fixed! Thanks a lot to everyone who contributed along the way.

Ended up buying a VCDS cable and a laptop, which was probably cheaper than those official Audi bloodsuckers.

Put the old climate control unit back in, read the coding, put the new one back in and applied the coding from the old one. Magic happened.

Then performed an adaptation, just to be on the safe side.

There's a couple of errors stored that I should get rid of, but that's a task for later. Also discovered an error on the fuel tank ventilation system, but that's a task for another day - already read up on the knowledge base article on the subject


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## MT-V6 (Jan 11, 2015)

Glad you sorted it.

Does your VCDS have a labels file (so when you code it pops up with info on what each digit does?)

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## jokskilove (Sep 10, 2013)

No, no extra information on what the coding means. Just crossed my fingers 

Here are the codes. When looking at the numbers, they look fairly unrelated, but in binary, it's just a few bits that have been flipped.

```
Old:   0524292 (decimal), 010000000000000000100 (binary)
New:   1573125 (decimal), 110000000000100000101 (binary)
MT-V6: 1049606 (decimal), 100000000010000000110 (binary)
```


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## MT-V6 (Jan 11, 2015)

Shame we don't know what they mean

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## SwissJetPilot (Apr 27, 2014)

If you go into the VCDS long coding feature, you may be able to determine exactly what the binary code changes mean.


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## MT-V6 (Jan 11, 2015)

The HVAC doesn't have long coding, if I remember correctly

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## chrislam (May 28, 2019)

Hi guys,

I have just done the retrofit of heated seats and have the same rear window demister issue. I have a vcds but for some reason the balloon for 08-hvac doesn't pop up so I can't code the controller as it is bringing up a short to earth fault. Can someone confirm that the controller with the heated seat buttons is manual climatic or auto climatronic and would you be able to post a picture of the hvac balloon for reference. Cheers, Chris.


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## beberobu (Aug 26, 2017)

Pretty close problem on mine TT now. I got a new (second hand) module from ebay, after i saved the scan i swapped the modules, seems to work but in VCDS says the engine can't see the HVAC module. I tried to code it but the old module have the same code in VCSD like the new module....

Address 01: Engine Labels:. 06F-907-115-AXX.clb
Part No SW: 8J0 907 115 N HW: 8J0 907 115 
Component: 2.0l R4/4V TFSI 0010 
Revision: 5BH16--- Serial number: AUX7Z0H4FNU0HN
Coding: 011300031C070160
Shop #: WSC 01236 785 00200
VCID: 377D122C46D44EF224-8062

1 Fault Found:
049508 - No Communications with HVAC Control Module (J301) 
U0164 - 008 - - Intermittent
Freeze Frame:
Fault Status: 00101000
Fault Priority: 2
Fault Frequency: 1
Reset counter: 255
Mileage: 0 km
Time Indication: 0
Date: 2000.00.00
Time: 31:63:63

Freeze Frame:
RPM: 0 /min
Load: 0.0 %
Speed: 0.0 km/h
Temperature: 55.0°C
Temperature: 30.0°C
Absolute Pres.: 1010.0 mbar
Voltage: 12.573 V

Readiness: 0000 0000

Then i tried to do the adaptation but there's not any available, when i click on "Adaptation" the list is grey and i cant access it. Someone living close to Leeds / Pontefract and dont bother to lose 30 min of his life if i ride to him for help with this?



jokskilove said:


> It's fixed! Thanks a lot to everyone who contributed along the way.
> 
> Ended up buying a VCDS cable and a laptop, which was probably cheaper than those official Audi bloodsuckers.
> 
> ...


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## MT-V6 (Jan 11, 2015)

Is the part number exactly the same?


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## beberobu (Aug 26, 2017)

Hi MT-V6!
No, the old part number ends in AG (8J0 820 043 AG)
The new part number ends in S (8J0 820 043 S)
Cheers!



MT-V6 said:


> Is the part number exactly the same?


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## beberobu (Aug 26, 2017)

MT-V6 said:


> Is the part number exactly the same?


Any idea?
Cheers!


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## MT-V6 (Jan 11, 2015)

beberobu said:


> No, the old part number ends in AG (8J0 820 043 AG)
> The new part number ends in S (8J0 820 043 S)


In theory this should be fine, though S is an older version

S was superseded by AG on 01/02/2008 and so should therefore be a direct replacement

There are so many versions it is hard to know what the differences are. Some differences include:

- prefacelift with smooth aluminium
- facelift with knurled aluminium
- temperature in degrees celcius
- temperature in degrees fahrenheit
- no heated seats
- with heated seats


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## beberobu (Aug 26, 2017)

Yeah, the problem is that it looks as should (identical with my older module) and it works ok (except the rear defrosting but this problem had it with my old module as well).
So, it works ok but in VCDS at 01 Engine i got that error, that engine cant see the HVAC module.
.....



MT-V6 said:


> beberobu said:
> 
> 
> > No, the old part number ends in AG (8J0 820 043 AG)
> ...


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## MT-V6 (Jan 11, 2015)

You say the engine has the communications fault, but can you access the HVAC directly with vcds?


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