# Smoothing Capacitor - Function, Diagnosis, Replacement [added to TOC]



## WillemBal (Nov 20, 2010)

I started this thread to address Matt’s question about the so-called smoothing capacitor, which he posted in the thread Developing-a-list-of-the-most-important-non-scheduled-maintenance-activities-to-do.
Although this particular capacitor may have a pretty low failure rate and normally needs no "maintenance", it may fail eventually, causing headaches to service technician searching for a cause of battery drain. I had put it on the list because electrolytic capacitors (after fuses) have the highest probability to fail of all electronic components. And it is the only basic electronic component which can be replaced in the Phaeton.

*The function and purpose of the capacitor*
The essential task of this capacitor, according to the self-study guide 272 “The Phaeton onboard power supply”, is to reduce the voltage ripple on the charge lead from alternator to convenience battery. More specifically, in the vicinity of the alternator, because of the large length (6 meter) of this lead. As we all know, the convenience battery is in the boot, while the alternator is at the front of the engine.
Since many consumers are powered relatively close from the alternator and relatively far from the convenience battery, the alternator ripple wouldn’t be “absorbed” as much as it would be when the battery would be located in the engine compartment (i.e. close to the alternator). Without this smoothing capacitor, the ripple could lead to electrical and acoustic faults. (our common name for that would be “gremlins” I guess…)

*Construction of a capacitor*
A capacitor is basically consisting of two plates, separated by an insulator. When a voltage is applied, an electric field between the plates is generated, which in turn causes it to retain its charge. This particular capacitor is an electrolytic type. The two plates are formed by two foils, of which at least one has a thin metal oxide film, which is both an excellent insulator and very, very thin. The advantage is that small capacitors can be made with high capacitance (indicating their ability to retain an electrical charge). The disadvantage of this capacitor is that it may start leaking. It may physically leak (electrolyte leaking out, forming a white corrosion deposit) or electrically leak between the two foiles. The latter causes a parallel resistance, basically counteracting its ability to retain charge. And what is worse, when the car is locked, the battery will be drained since the capacitor is connected directly in parallel with the convenience battery.
Another disadvantage worth mentioning is that it is polar. In other words, it has a + and a – connection, just like a battery. When you take it out and inadvertently put it back with reverse polarity, it will be damaged (best case), get hot and even explode. The battery’s ability to supply sufficient current to make this happen is enormous. So if you ever decide to take it out, please watch the orientation of the text on top cover. It should be readable from where you are standing.

*Diagnosis*
The best way to diagnose a possible problem with this capacitor, is to measure the current drain of the convenience battery while the car is fully locked. About one or two minutes after locking the car (no fans running), the current should drop to an idle current of about 35 to 50 mA. There is a very expensive tool which which this can be done, and this is called a "current clamp" or clamp-on current meter. It has two jaws which clamp around the lead through which the current flows you want to measure. The more expensive ones are able to measure within a small current range, the cheaper ones measure up to very high currents, 100 Amps or more, but are not suitable for our purpose.

Once you have diagnosed a higher than normal current, the capacitor is one of those components to suspect. Simply take it out (simpler said than done...), then measure again the current.

An alternative method to diagnose a leaky capacitor is by taking it out (I would do that with the battery still connected), then measure the voltage on the capacitor. It should be same as the battery itself and slowly discharging (because of the load of your DMM). Put it away (avoiding short-circuit of the two pins) and leave it for a couple of minutes. Then measure it again: the voltage should still be the same as before.
After you have confirmed it is OK, once again pay careful attention that you do NOT install it the wrong way! When you put it back correctly, you might see a tiny spark, which is normal because the capacitor might be partly discharged due to the internal resistance of your DMM.

*Location*
The capacitor is located in the e-box in the right air intake plenum chamber. You can’t miss it; it is the only round component in there and it is about 25 to 30 mm in diameter.

*Smoothing Capacitator*









The actual capacitor is located in the upper left corner, left to the two relays with the text "100" on it. Further down this post, there are two photo's of the removed part.

I noticed that none of the drawings in repair manuals etc. actually shows this component. In fact only the position of the fuses matches what is inside the e-box. The only good component location diagram is given on page 11 in the SSP 272 : The Phaeton Onboard Power Supply

Part number is 3D0903291 and it looks like this:










and this










*Replacement*
It can be easily removed from its socket and installation of a new one is almost as simple as replacing a fuse. However, please note what I stated above about the polarity of the capacitor. Please make sure that you can read the text of the capacitor when you put it back. As you can see on the first photo of the e-box, all components have identical text orientation (except some fuses, which may have been replaced by someone who was not aware of this basic rule). 

Willem

_Edit by Michael - Photo replaced with better photo of the capacitator_


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## PanEuropean (Nov 3, 2001)

Hi Willem:

Wow, what a useful, interesting, and informative post!

Thanks a whole lot for writing this up. I know that one of our forum members (Matt from Wisconsin) is trying to troubleshoot an electrical current drain problem right now - I am sure he will be very grateful for this information.

I'm going to go digging around to see if I have a better picture of that part somewhere in my library.

Michael


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## PanEuropean (Nov 3, 2001)

To get access to the electrical box that is located in the cabin air intake plenum, some dis-assembly of the car (_NOT _quick and easy!) is required.

This post, which is listed in the Phaeton Forum 'Table of Contents' (FAQ by Category), explains the dis-assembly process: *How to remove the Plenum Chamber Cover*. 

Be *VERY *careful when removing the large slotted plastic piece that fits into the groove running across the bottom of the windshield. You can easily break the windshield while trying to dislodge this part - especially if your car is now 7 or more years old, and especially if the part has never been removed before!

Do not attempt to remove this part unless the car is at room temperature (70°F, 20°C). 

Michael


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## Riffe6506 (Oct 21, 2009)

*Will Test capacitor tonight - any info on part no. 3D0 937 049?*

Thanks Willem and Michael,

I think I can get at the capacitor to remove it and test. Looks like I might even be able to get at it without removing the 2nd cover - but if not I have the instructions on how to do it without breaking the windshield. Thanks!

Just to make sure I am reading correctly - it would be ok to operate the vehicle without the capacitor installed as a means of diagnosing if it is indeed faulty?

Also, my VAG-COM has fashed the following:

Address 09: Cent. Elect. Labels: Redir Fail!
Part No: 3D0 937 049 G
Component: STG.Bordnetz 5001 
Coding: 0000002
Shop #: WSC 01065 000 00000
VCID: 2E5DF397C08C

My VW dealer has listed part no. 3D0 937 049 as the "power control module." Do you know where this part is located - and if so, is there a procedure for removal / testing / replacement? 

My review of the forum leads me to believe it is in the passenger side footwell - but initial inspection has left me clueless on what to start tearing off first to get at it! If it is in the plenum chamber - maybe I can kill two birds with one stone.

Is this a part that you have seen go bad before and if so did it lead to battery drain and a host of other faults?

I have been pulling my hair out on this one for well over a year. replaced the alternator, battery control module, update all software....

My VW dealer literally hides when they see me coming now. 

Despite all the setbacks - I can't help but feel I am getting closer!

Thanks again for your assitance.


Matt


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## Riffe6506 (Oct 21, 2009)

Just to make sure I am reading correctly - it would be ok to operate the vehicle without the capacitor installed as a means of diagnosing if it is indeed faulty?


Willem,

Please disregard this question. I read again and realize i am stupid. I need to measure the voltage of the capacitor and re-install.

Sorry,

Matt


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## PanEuropean (Nov 3, 2001)

Riffe6506 said:


> ...My VW dealer has listed part no. 3D0 937 049 as the "power control module." Do you know where this part is located - and if so, is there a procedure for removal / testing / replacement?
> 
> My review of the forum leads me to believe it is in the passenger side footwell - but initial inspection has left me clueless on what to start tearing off first to get at it!


Hi Matt:

The part you refer to is controller 09, the Central Electrical Controller. If there is a problem with this controller, the problem will be reported on a diagnostic scan. In the absence of a report of a problem with it, I would work on the assumption that it is OK. I think Willem's analysis that suggests the capacitor as the source of the problem is very credible and should be thoroughly investigated before you go any further. I can't imagine that the capacitor is an expensive part - if it costs less than $50, I'd just buy a new one and install it, to heck with analyzing the existing one.

The Central Electrical Controller is located on the forward, sloping face of the passenger footwell. To get access to it, you peel back the carpet (starting at the very front, top edge). This will reveal a large plastic panel, you then remove this panel and the controller is behind that. But... there are no 'serviceable' parts associated with the controller.

The photo below shows the front passenger footwell of a left hand drive car. The carpeting has not yet been installed (this picture was taken during initial assembly of the car). You can see the large plastic panel that comprises the sloping forward surface of the front passenger footwell. It is held in place by about a half a dozen fasteners, all of which are easily seen. If you remove this panel, you will find the central electrical controller behind it.

Michael

*Front Passenger Footwell - Controller 09 is behind the large black panel*


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## PanEuropean (Nov 3, 2001)

Here's a better view of what the carpet looks like when you have peeled it back from the front passenger footwell. I took this picture as part of a series of pictures describing How to Retrofit a Fire Extinguisher to a Phaeton, and when I did that work, I removed the entire front passenger footwell carpet - that was essential to fit the fire extinguisher.

It is certainly not necessary to remove the entire carpet to get access to the Central Electrical Controller, but you may need to remove the trim panel that runs longitudinally beside the transmission tunnel (visible at the far left of this picture) in order to remove part of the carpet that covers the side of the transmission tunnel. Maybe, maybe not - it all depends on whether or not you can reach the inboard fasteners for that large plastic plate with just the forward surface of the carpet pulled back.

Michael

*Carpet on Forward Face of Passenger Footwell Peeled Back*


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## WillemBal (Nov 20, 2010)

PanEuropean said:


> I can't imagine that the capacitor is an expensive part - if it costs less than $50, I'd just buy a new one and install it, to heck with analyzing the existing one.


Hi Michael,
Price is € 38.56, or 53 US$... So just above the 50 US$ limit.
I fully agree with your suggestion to just heck with analysing the existing one and instead just replace it. I guess I didn't realize that it is an easily obtainable part, with moderate costs, while it is difficult for someone to diagnose a problem with it, without having the proper tools and electrical background. Especially when there are problems with the electrical system and this cover is off anyway, one might as well decide to replace it, just to be sure it cannot be the cause any longer.
Willem


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## Riffe6506 (Oct 21, 2009)

*Ordered capcitor*

Ok guys - I ordered the capacitor this morning. $48 - plus another $20 to get it here from Germany. Apparently a part not stocked at any dealership and must be ordered from factory. Will take 2 weeks to get here. I will have my fingers crossed until then.

Michael - you stated "The part you refer to is controller 09, the Central Electrical Controller. If there is a problem with this controller, the problem will be reported on a diagnostic scan. In the absence of a report of a problem with it, I would work on the assumption that it is OK."

I mentioned before that I recieved the following reading from the VAG-COM:

Address 09: Cent. Elect. Labels: Redir Fail!
Part No: 3D0 937 049 G
Component: STG.Bordnetz 5001 
Coding: 0000002
Shop #: WSC 01065 000 00000
VCID: 2E5DF397C08C


Does the "Labels: Redir Fail!" not indicate a fault or failure of this component? A better question might be what does the "Labels:" section of the VAG-COM readout mean. I understand that when a fault is found - it is listed under the controller number, part no. coding, shop, etc.... But this is the only component that came back with the message "Redir Fail!" after the "Labels:" All the others had the part no. with a suffix in this field.

Probably a dumb question - but any help is appreciated as always.

Thanks,

Matt


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## PanEuropean (Nov 3, 2001)

Hi Matt:

"Redirect Fail" is an internal VAG-COM fault code (nothing to do with the car) that indicates that the VAG-COM application has not successfully looked up the 'label file' that the application has on record as being associated with the controller.

The 'label file' is a plain-language elaboration of coding and adaptation fields in the controller. It is used to make the process of coding and adapting controllers more simple and intuitive. All fault codes will be correctly identified and reported even if no label file is present for a controller.

I wrote most of the label files for the Phaeton. An example is attached below, it is the label file for steering wheel electronics (controller 16). It is a text file, you can open it and read it with any text editor (Notepad, Microsoft Word, etc.). When the VAG-COM program is installed on a computer, these files are stored with the suffix .lbl, rather than .txt.

I have no idea why the redirect is failing for controller 09 - I will investigate this later when I have time.

Michael


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## Riffe6506 (Oct 21, 2009)

*Didn't fix it - !^%#^%!^*

I installed the smoothing capacitor - an easy swap that did not require the removal of the "2nd cover" that attaches to the windshield. It was easy enough to just reach in to change it out. Take note that it is not enough to trust the label on the capacitor in order to know what direction to put the new one back in - rather, take note of the "notch" that is pressed in to the casing - and the positve and negative marking on the terminals. The label on the new capcitor was not aligned the same as the one that was in the car. I have pics I will post soon.

Still have a parasitic draw on the left side battery. 

The saga continues.

Regards,

Matt


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## Jesped (Feb 20, 2012)

*battrery drain*

Hi there. 
Reading this forum and while looking for a possibly solution to my, just upcome problem finding a lot of nice information I didn't know I'd like to know about, example how to put Phaeton into jack-mode (my manual is in German and I don't really understand that language in writing, well ther will be many language I don't read too good ------ English is in the greyzone ) ), Thank you for that and many more hints ) 
But I didn't find that anyone ever catch the gremlin that sucks about 4 amp from the left battery! Cos I've got one of those right now!
Did anyone ever?
I've had my used Phaeton V10 tdi -05 for, a bit more than two years and, until now had no electric problems worth mention (only sparking love at first meeting) 
I imported the car myself from Germany to Sweden, bought from VW dealer.
But now this extreme battery-drain problem.
.
I've testing the capacitor as described and it keeps the power for a long time, I've taken out all fuses and relays but whatever I do, the batterydrain seems to be constant, about 3 to 4 amps (and that is heavy). 
I can not, not easy get to the alternator for disconnect but I measured the temperature with ir-instrument and it seems to keeps same temperature as other parts also after a cold night outside. 
For you might wonder, where I live, which is south Sweden would be like south of Canada or north of USA I think.
.
I have access to the Vag-com tool but gets so many fail-messages after battery drain that it really is not usefull for my litle brain.


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## Gabs08PHTN (Jan 6, 2011)

Hi Jesped,
First of all: do you measure the current consumption shortly after you have swiched off the ignition and locked the doors, or do you measure it after lets say 20-30 minutes? The second is the correct, because it can take up to 20min for all the control units to go to sleep.
Also, how old are your batteries? It is been recommended in this forum that they should be replaced every five to six years in order to get rid of most electronic glitches.
If your issues still persist, search for "Battery Drain" in the forum. There are several post covering this matter.

Gabriel


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## invisiblewave (Sep 22, 2008)

I recently replaced my battery based on those recommendations, and against my better judgement, and it wasn't a battery problem. How do you measure the draw on the battery? I suspect there's a small draw on mine somewhere that is causing load management intervention during starting, and after reading this thread I'm thinking about checking the capacitor.


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## Paximus (Aug 26, 2011)

The Bentley Flying Spur instructions for measuring the left battery quiescent drain current are quite readable (NB: this list has been lightly edited by me):

1. Use a DC clamp-probe test meter with a capacity of 500mA with accuracy +/- 2%.
2. Fully charge the left battery. Use the Midtronics WT10103 battery tester to confirm.
3. Turn the ignition off and remove the key. Close all doors and lids (except power trunk).
4. Connect the current clamp tool around the left battery negative lead.
5. Close the trunk lid to latch the lock, without unduly pinching the test leads. A manual trunk lid must be latch-locked by hand, but the lid may stay open.
6. Lock and arm the car using the key remote. Put the keys out of 'earshot' of the car.
7. Wait a minimum of 20 minutes for the systems to settle into their lowest communicative state.
8. Read the quiescent current. An acceptable reading is anywhere below 40mA.


It is probably not possible/practical to take a reading by disconnecting the battery lead and inserting a milliamp meter in series, because the car will detect the disturbance and stay awake. At certain times the readings could be in the order of 40A, which would damage an inserted sensitive current meter.

Chris


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## Jesped (Feb 20, 2012)

My left battery is new, bought because I was convinced a drained out battery would be caused by old age. But both (old and new) can be charged to 13.7 V. I am pretty sure the problem isn't related to the batterys. I also tried starting without left battery so right battery (starter) takes over all consuming with results, a drained out right battery, also within 16 hours, maybe less.
My DC clamp-probe tester isn't expensive enough to messure as low amps as 40 mA but since I can read 3.75 A (and immediately after closing the car around 5 A) it will do fine this far. 
At this time I have the extra-battery in the trunk .. a set of starting cabels and two chargers as well, the fuse and relaybox is lifted aside - It really looks messy 
I connect the two batterys +poles, then I connect the -poles, from here I can disconnect the installed battery by loosing the -poleshoe. Now I have the power through the startingcabels and can hang them out when closing the trunk. Clamp the cabel and measure the drain.
.
In the beginning I just tried to pull out fuses (a lot) to see if any change .. there was not! Empty battery next day whatever which and how many fuses and relays pulled out. Nor did pulling out the Capacitor make any difference.
But - pulling out fuse no. 83 (fusebox under instument panel) for Digital Sound System Control Module (Phaeton don't know driver's door is open) .. stops the drain. My meter drops from 3.75 A to 0.03 A .... When I found this I was quite excited ... for a while. Because after, maybe 10 minutes the drain starts again - back to 3.75 A. But I'm sure I am the gremlin on the track.
I read about someone finding a free TV module causing problems .. some kind of module making it possibly to watch TV while the car is moving. Well, my TV isn't working, I figured it would be because the receiver is analogue but now I find that I actually have the hybrid receiver. I can't however get the TV to respond on the remote ... but the flickering picture is there whatever the car is moving or not! Maybe someone installed a gremlin for watching TV on the move? If it's so, where would it be located? 
(disconnecting the TV module didn't make a change)
.
:banghead:


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## PanEuropean (Nov 3, 2001)

Hi Jes:

Welcome to the forum community!

Thanks very much for sharing the information about the battery drain coming from the sound system - that is fascinating information, and certainly something that is new to all of us.

Be aware, though, that the Phaeton will "wake up" (even if the ignition is turned off) if any of the controls related to the sound system are pressed after the ignition is turned off. It will then remain "awake" for up to 55 minutes. There are two different "wake cycles" possible with the ignition turned off. One is for 1 minute 55 seconds, this happens whenever a door handle is activated (including touching keyless access door handles with an authorized key nearby). The other is the 55 minute (might be 1 hour 55 minutes, but I think it is only 55 minutes) wake cycle, this happens if an entertainment control of any kind is operated after the ignition is turned off.

What I am getting at here is that you may have inadvertently "woken the car up", and as a result, you are seeing a normal, by design electrical demand from the sound system.

Best way to rule this out is as follows:

*1) *Put a battery charger (maintainer) on the left battery. It's OK to leave the trunk lid open.

*2)* Hook up your electrical measuring device to the sound system circuit that you discovered the electrical drain on. Close all the doors, lock the car, if you have keyless access, move the key fob out of reception range of the car.

*3)* Leave the car alone for 2 hours or more. Then, have a look at the electrical measuring device without touching any door handles or other car controls. See if the electrical drain is still present.

Michael


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## Jesped (Feb 20, 2012)

I think I've did all that allready Michael, I've been reading in this forum for a while and I think I understand Phaetons sleeping procedure. 
But I notice, when gearshift is in neutral a message will appear "put level in parking position" .. This will turn off after a while - but any touch of handle (Key out af reach) it will light up, well at least as my Phaeton react now (with the disease it has)
"Eskremsky" mention a - TV-free adapter - in #http://forums.vwvortex.com/showthre...attery-drain&highlight=left+battery+solution# 
Where would this, if one of those is present in my Phaeton, be physically? I want to check out if the gremlin lives there .. Since my TV don't seem to work as it should and that is connected to the Digital Sound System Control module (it must be) it feels like a good idea to look further into that area..

Actually occurred my problem a few days after borrowing a badly electric wired trailer ... but I tried disconnect the trailermodule with no luck and everything, works fine now with both my own caravan, boat trailer and the local lumber shops free trailer. Yes, in the middle of it, I am about to restore our kitchen since my wife didn't take new curtain rings as a reasonable compensation for my bike, boat and car :laugh: And 3 days ago my 7 year old cat was run over dead It's a lot for a guy with ten thumb and only one brain.
At the time with the first trailer .. I measured for power in the trailer coupling and couldn't get 12 V anywhere .. well, I didn't think of this as more than - it's a Phaeton. But now, when I measure the same .. I've got 12 V from 2 pins - and with the adaptor 1 pin (Phaeton, like many newer cars has 13 pins but my trailers has 7). Maybe this is different over there? 
.
By the way .. I've read a lot of posts you wrote in this forum Michael, and learn a lot. Many thanks - you are great :thumbup:

/Jes


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## PanEuropean (Nov 3, 2001)

Jesped said:


> ...when gearshift is in neutral a message will appear "put level in parking position" .. This will turn off after a while - but any touch of handle (Key out af reach) it will light up


Hi Jes:

That's normal behaviour on any Phaeton that has keyless access. I believe that touching a door handle (with or without a key present) wakes the car up for 55 seconds (or 1 minute 55 seconds, if that is the correct time). The keyless access system does have protection built in against repetitive, frequent touches of the door handle - if the door handle is touched too often the car will just shut down the keyless access system and ignore further touches until a certain period of time (I don't know how long) has elapsed since the last touch. This is to prevent battery discharge due to a fault in a door handle.



Jesped said:


> "Eskremsky" mention a - TV-free adapter - in #http://forums.vwvortex.com/showthre...attery-drain&highlight=left+battery+solution#
> Where would this, if one of those is present in my Phaeton, be physically?


I don't know. It is an aftermarket component. We were never offered TV as an option here in North America, hence I am not familiar with aftermarket TV components. In any case, an easy way to check and see if you have such a device installed is to just select TV on the display screen (even if all you see is static), then start driving. If you see a message indicating that the TV picture cannot be displayed for safety reasons appear as soon as the car is going faster than 5 km/h, then you don't have that gizmo installed.

By the way, Willem Bal is an absolute _wizard_ of electronics - he has a Ph.D. in the subject - so, I would put great faith in the comments he has made on the discussion you cited above.

I want to check out if the gremlin lives there .. Since my TV don't seem to work as it should and that is connected to the Digital Sound System Control module (it must be) it feels like a good idea to look further into that area..



Jesped said:


> Actually my problem occurred a few days after borrowing a badly electric wired trailer ... but I tried disconnect the trailer module with no luck and everything, works fine now with both my own caravan, boat trailer and the local lumber shops free trailer.


We were not offered trailer controllers (controller 69) in North America either. I think, though, that the trailer controller is probably innocent and it is only coincidental that the problem appeared after your difficulties with the poorly wired trailer. One of the main jobs of the trailer controller is to protect the car against poorly wired trailers. In any case, the fuse supplying power to the trailer controller is fuse SC9 (fuse 9 in the panel above the left battery - it is the top-most fuse in the second row from the rear. You could pull that fuse and see if the problem goes away, or alternatively, you could monitor that circuit for parasitic power draw.

You mentioned that you have access to a VAG-COM. May I trouble you to run a scan and post the results here? Have the engine running when you do the scan. Best to do two scans: The first one will probably have a lot of 'intermittent' faults listed. After you do the first scan, choose "clear fault codes" and that will get rid of all the intermittent ones. Then do a second scan, and post that one. Easiest way to transfer the scan results from VAG-COM to the forum is to 'copy' the scan result from the scan page of VAG-COM, then paste it into a blank text document. Then just copy the whole text document into your post here.

Michael


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