2008 S6 - O2 sensor or something else?

A6 All/ S6 All
#1

Hey guys!

Quick intro here first: I was a long time member over at AudiForums in the A6 subforum and would try to help fellow C5’ers out whenever I had the time. I had an 03 A6 2.7T and just recently traded her in for an 08 S6. It was hard letting her go given how much time and work I had put in to her, but it was only a matter of time before a turbo went and I would be stuck with dumping in several grand worth of parts and several weekends of time pulling the engine and doing the install. So I did what any sane Audi enthusiast would do and buy an even more expensive-to-maintain beast such as the 5.2 V10 ;D

I took the car to go get inspected at my local indie shop who specializes on all German makes and they come back telling me it’s a faulty O2 sensor and the engine needs to be dropped. However I’m not convinced that is the case. Take a look at the most recent set of codes I pulled today from the car:

It is also important to note that the paperwork the shop gave me also indicated that cylinders 4 & 8 were also producing sporadic misfires. Also, at the time of the above scan with VCDS all monitors were set and complete. They have yet to re-set given it has not gone through a complete on/off cycle as the car was hot when cleared by me.

I have identified a taped up PCV hose on the driver’s side cylinder head (Previous owner/shop obviously broke it) which is causing a slight vacuum leak, along with a fairly significant vacuum leak from the oil separator (I pulled the oil fill cap off and heard the loud wooshing of air from the oil separator).

My question is am I on the right track here that this random lean/rich codes are attributed to the vacuum leaks and not a fouled up O2 sensor? I see a clear pattern here that everything is occurring on bank 2, so at this point I do not think their diagnosis of an engine drop is correct.

And if it is well, there might be a good chance I’ll put together a detailed DIY on removing the 5.2 ;D

Looking forward to any help and also looking forward to being able to return the favor to the 5.2 community here!

#2

Oh, and I know the stigma associated with that forum. Trust me, I pretty much gave up trying about a year ago after trying to help one guy out who just didn’t take any advice of mine even though I was the only one replying to his rants. Glad to have found AR!

#3

Welcome to AR. We are glad to have you. lots of members are coming here. I and almost all the others got sick and tired of the drama and BS on other sites. Add to that the lack of real information and support. espically with the V10 as we say on AR if you find AR helpful try to find another good guy to save and bring over here. The more V10 guys the better.

As for your car. If you have a vagcom that is going to be very helpful.

The V10 cars are very solid once you get some of the gremlins out of the way. There are a growing amount of performance products available and theres a lot of good guys and technical guys here to help.

For starters the 02 is not failed baised on the VAG code. So putting your motor baised off what you have showed would be a huge waste of money.

To see whats going on. Clear the code and see if it comes back right away.

Do you have a vag com. I can tell you what to do.

#4

That is what I’m noticing very quickly… lots of good knowledge here whereas other places it’s hit or miss. Glad to have found AR!

I’m glad you agree that the engine doesn’t have to be dropped. I didn’t think so either based on what I found when looking at it myself. (Should have done it before taking it for inspection but I was a little lazy, I’ll admit)

In regards to Vagcom, yes I have it. I have cleared the codes and nothing came back after a 20/25 mile test drive yesterday evening. This morning I verified that the monitors have all reset, which indeed they have. Still no codes.

I’m thinking this wreaks of a phantom/intermittent vacuum leak based on everything going on…

#5

Justin! Long time no talk! LOL!

So here we are about 6 months later and I’m sorry to report back that I’m still having issues with my 08 S6. Sorry to have to bring up such an old thread, guys! Hectic summer/fall! Switched jobs, got a new car, new house… so I’m finally getting around to doing some more work on this beast.

So I have some more up-to-date logs from VAGCOM. See below:

p2098 presented itself this afternoon while driving on the highway at around cruising speeds. p300 appeared once I had the car in my garage idling and took the oil fill cap off. You could tell it was struggling and a loud “hiss” could be heard from around the back of the intake. I tried using some carb cleaner to see if I could identify a vacuum leak but really wasn’t able to turn up anything significant. Actually, nothing to be precise.

Right before I moved I changed all 10 plugs and coil packs since I did not know when they were last changed by the previous owner. Also, while I was in there, I changed the oil separator along with the hose that connects both cylinder heads because I noticed some cracking that I thought might have been causing an intermittent vacuum leak. To my knowledge carbon cleaning has not been done on this car - but would that cause these symptoms? This seems like a classic vacuum leak but I cannot seem to track it down,

I’m a little stumped at this point based on the data I’m seeing in VAGCOM and what I’ve been able to (or not) replicate in the garage.

Any of you follow V10 guys have any ideas? I’d be willing to give anything a shot at this point - just point me in the right direction!

#6

Oh! Forgot to mention… I did just install a new battery this morning. It’s been getting colder here in the north east US and there were a few times I could tell it was really struggling to turn over. Charging system seems fine.

#7

Did some more investigating and had a look at measuring blocks 32 and 33 for the o2 sensors and it appears to be a vacuum leak as I suspected. I cleared any codes that were present and them immediately went over to 32 and 33 to see what was going on. I started logging about 15 seconds after the engine had been running since all codes were cleared.

Can one of you fellow V10 guys check out the CSV file from vagcom to make sure I’m not going crazy here.I put it on Google drive since it looks like the upload folder on the forums is full: https://drive.google.com/open?id=0B11FCJo2lr2ES25EUDhXVFJRQWs

After the winter I’m going to perform the carbon cleaning and probably get me some JHM intake spacers since I’ll be in that area anyway. I work from home so I don’t anticipate putting too many miles on it between now and March. Maybe an additional 1000 at most.

#8

One of the first thing you might want to do is like you said a carbon clean and toss in the JHM spacers. The carbon clean will help the car start and run better in the cold. If the car has a vac leak it will have issues starting.

The missifres make more sense when you consider you might have a carbon build up issue. Also if you have a vac leak you generally see fuel correction codes. The issues you might be having can be related to bad injectors. That is also a big issues that comes up if you dont have a carbon clean. Its worth checking into.

My advice would be to pull the intake check the carbon send the injectors off to be cleaned. Get everything back drop in the JHM spacers and inspect your intake manifold to make sure its not broken

#9

Thanks, kind of what I’m leaning towards as well in terms of really getting a better sense of what exactly is going on. Lord knows if the previous owner EVER did the carbon cleaning.

I will keep this thread updated as I keep digging away. The more info the better since there’s not a ton of info on these 5.2s out there.

#10

Yes the more info we can gather the better. We are really starting to get a lot of good data and the formula for getting these little issues and bugs worked out

#11

Little bit of an update here on this topic.

Slowly but surely I’m starting to get to know my S6 a little bit more each time I have it in the garage. Little bit after the Thanksgiving holiday I decided to have a more thorough investigation looking for a vacuum leak and lo and behold I found a sneaky leak right in between the throttle body and intake on bank 2 - right between the mating surfaces.

Anyone with experience on this setup knows where this is going already. The top two bolt holes on the intake were stripped out!

I did what any other Honda Civic owner would do and went to Auto Zone and got a heli coil kit and prayed to god that it would actually work (I knew if not it was going to mean forking out some decent cash for a new intake). I was actually surprised how well the heli coil kit worked and was able to torque the bolts back on properly.

So now I only get one code (Lean, bank 2) as opposed to both lean and rich codes on bank 2, which I suppose is a step in the right direction.

I ordered a new throttle body gasket from ECS and installed it tonight and re-checked the area for vacuum leaks and got the same result. Idled at around 660ish, up to 700 then down to the low 500s. I am assuming that when the previous shop/owner stripped the bolt holes they also ever so slightly warped the intake mating surface.

To try and see if indeed that is the source of my CEL, I smothered the suspected area with some ultra grey and am letting it cure (I literally used my finger to apply it over the crease of the mating surfaces… not around the gasket itself). If I find that this is the case I might disassemble it again and put a thin bead on both sides of the gasket and see what happens. I realize this isn’t ideal but I cannot bring myself to spend almost 2k on a new intake. I’ll wait until one of the internal actuators goes then do it ;D Unless of course, anyone has any input/ideas on this?

Sorry for such a long-winded post on such a seemingly simple issue.

#12

Not sure if I mentioned before, but I had the same lean codes you have for bank 2 and eventually for bank 1. this was an issue that was due to intake failure. Car still ran fine, but the CEL would come back within 20-50 miles each time it was cleared. I think the only resolution would be a new intake manifold as that’s what I had to do and I just passed emissions testing. Hopefully you can find some other way as it was not cheap. JHM has the best discount as far as I know, but godspeed my friend.

#13

Good update. Every little bit of information helps us get a better idea on what is going on. The throttle body leak you can put a small bit of RTV on the gaskets to help them seal if you need to.

As Six6Six said if your intake manifold is bad that can be part of the lean codes. Also you can get lean codes for issues with injectors. But the best first line would be to make sure your not getting any vac leaks anywhere in the system

#14

I realize that a new intake might indeed be what is needed to remedy this. Just the nature of the beast, I suppose.

Confirmed that the RTV I smothered in between the two mating surfaces does indeed work. I sprayed it down with some brake cleaner at idle and it didn’t increase/decrease RPMs. Showing some promise there. If this works I will take it apart again and put a thin bead of RTV on both sides of the gasket so it doesn’t look like complete crap.

I did have a lean code that was stored in the ECU but did not produce a CEL. Though I’m not sure if it was before or after the application of RTV. I should have broke out my laptop and pulled the freeze frame data but was lazy and used my cheapo Bluetooth scanner to pull it. I’ve cleared it and will see if it returns during the next few drive cycles.

#15

Drove about 75/80 miles and checked for any pending codes and didn’t get any - this is good news!

My theory is that yes, carbon cleaning was done on the car prior to me taking ownership of it this past June @ 100k miles, but the down side is they weren’t really careful in reassembling the intake.

I will continue to keep an eye on any pending codes/CELs, but hoping this was indeed the issue. I will wait another several hundred miles before taking off the throttle body again and doing a proper application of RTV so it doesn’t look terrible in the engine bay.

Once the weather gets nicer in the spring I will still take off the intake to verify my thought process around carbon cleaning. I’m one of the lucky few that get to work from home so it’s not a HUGE deal as I will only put on maybe 1k miles between now and then.

Thanks for all the input thus far - much appreciated. If anything pops up I will be sure to keep this thread updated this way we have a record for future people who may possibly run in to the same issues as me.

#16

Its nice to hear the RTV might have fixed the leaking issue for now.

When it comes time to do the clean or more work let us know. If we can help we are happy to

#17

Sorry to bring up an old thread, guys… But I figured this is the best course of action in case there’s someone else out there with a similar problem as mine they can see everything documented in one thread.

I’m pretty sure you hit the nail on the head, SIX6SIX.

So I bit the bullet and pulled the intake off to do the carbon cleaning that every one of us S6 guys has to do at one point or another. Sure enough I found a piece of the intake wedged into one of the intake ports. I went ahead and ordered a new intake (Ugh!) from JHM (I did not opt for the intake spaces this time due to cost restraints) and installed it last night after work.

So far so good. Car seems to idle fine and doesn’t appear to have the sluggish idle after the SAI pump turns off after a cold start.

I still have a few odds and ends to do on it tonight as I ran out of daylight. I will report back my findings afterwards and will be sure to update this again after I’ve gone through several hundred miles to see if the CEL comes back.

Just super excited to get this out of the way… been a long time coming! ;D

#18

Glad to hear everything worked out great. Hopefully nothing but happy motoring from here on. The intake spacers, not mandatory, but good if you ever do track time or do a lot of sports mode driving in warm weather. Outside of that, hope all is great for many thousands of miles to come.

#19

So unfortunately there are still some kinks to iron out. I am still getting 2 codes:

The above was taken from ECU1. There were no codes stored in ECU2. I believe there was another thread where Justin covered how different ECUs monitor different banks of O2 sensors since our cars essentially have 8 sensors, or 4 banks. Just to be clear, can anyone chime in on the above? Is my car throwing codes for the passenger side (I’m in the US) bank of cylinders since this was pulled off of ECU1?

Where do you guys suggest I go from here?

Is this the hallmark sign of injectors sticking open/closed? Could one of the high pressure fuel pumps be on their way out? Some kind of crazy hard to find vacuum leak?

Really kind of stumped on this one… any help would be appreciated at this point guys!

#20

…Always seem to post again like 10 minutes after my update.

Re-reading the above replies the common theme are injectors. Is there any way in vagcom to verify for certain that the injectors are on their way out? When I had the intake out I could clearly see that the previous person who was in there before me left a bunch of the blue o-rings in there from when they swapped/serviced the injectors. I bought the car with about 95k miles on it and she has about 105k now. I held off on getting injectors from JHM because of the evidence I saw when I had everything taken apart. I assumed the previous owner had the injectors changed around 60/70k miles and thought there was no way they could have gone bad already between now and then.

I have a funny feeling I will be taking the intake off again soon. That’s what I get for trying to save another $600-ish.