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Has Anyone Replaced pre-cat Lambda (Oxygen) Sensor Without Removing Manifold?

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Old 06-11-2014, 04:45 PM   #1
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Default Has Anyone Replaced pre-cat Lambda (Oxygen) Sensor Without Removing Manifold?

I think I need to do both "upstream" or "pre-cat" sensors. Bentley says it's necessary to remove the intake manifold. I wondered if it's possible to avoid this, since I'm a lazy American

Precious little info here and hard to search since it's variously called O2 sensor, Lambda probe, Oxygen sensor, B1S1 & B2S1, as well as HO2S and G108; but I am an eternal optimist.

TIA,
Tom
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Old 06-13-2014, 05:43 AM   #2
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I have exactly the same question and concerns! It is surprisingly hard to aggregate the info through the search function and google is worthless since you have to wade through 11 million different parts houses trying to sell you an Oxygen sensor.

aTOMic is yours a 4.2l?

Mine is an '05 quattro base and I want to change out all four.
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Old 06-13-2014, 11:27 AM   #3
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Yes, 4.2 "PETROL" as opposed to the 4.2 diesel offered in Europe; you can go to Google Advanced search and limit searches to Audiworld.com or A8parts.com, or use the "-shipping" in your search to almost eliminate shopping/ad results; but you'll see there is not a lot of info. I'm afraid there is no way to do it without removing the manifold.
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Old 06-13-2014, 12:18 PM   #4
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Originally Posted by aTOMic* View Post
Yes, 4.2 "PETROL" as opposed to the 4.2 diesel offered in Europe; you can go to Google Advanced search and limit searches to Audiworld.com or A8parts.com, or use the "-shipping" in your search to almost eliminate shopping/ad results; but you'll see there is not a lot of info. I'm afraid there is no way to do it without removing the manifold.
Ooooh clever! Google has been getting crazy spammed lately.
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Old 06-16-2014, 07:16 AM   #5
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Has anyone done the pre-cat sensors (DIY) - even going by the book and removing the manifold - that can provide me any tips?
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Old 06-16-2014, 08:08 AM   #6
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I can tell you that you can do both pre-cat sensors on a D2 A8 40v motor from the top of the engine bay. You just need a good O2 sensor wrench and some patience.
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Old 06-16-2014, 08:47 AM   #7
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I can tell you that you can do both pre-cat sensors on a D2 A8 40v motor from the top of the engine bay. You just need a good O2 sensor wrench and some patience.
Thanks Paul!
Does the D2 manual procedure call for removing the manifold?

What do you mean by "Good" wrench... crowfoot, flex/wobble extension, or just the socket with the slot for the wire?

On the D3 I cannot even see the left one even with all the vac and other hoses d/c'd... but I have not removed the main intake hose I confess...

Thanks again,
-Tom
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Old 06-17-2014, 08:50 AM   #8
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Default What PaulW says is true, BUT...

PaulW is presumably right on the D2's. Same thing on my 2000 A6 4.2; I did both sides with basically everything in place, essentially up on top of the intake crouched under the hood reaching down. Pretty much done by feel/blind.

BUT, this knowledge may not be transferable to the D3. It's why I didn't respond earlier. Plus, obviously w/ a W12 it's different. Smog regs changed after 2003 in the US. It basically forced Audi to move the first cats up close in to the head instead of way downstream like they used to be. It's why there was never a 2004 RS6 in the USA, even though they shipped more in Europe. Thus, I expect the D3 4.2 to be like that since they would have complied it to the newer rules, and then probably change the O2 set up and exhaust manifold some.

If you search over on QW D3 board BTW, one guy says he did it w/out pulling the intake manifold. No details in the post though. Having pulled my C5 4.2 manifold a few times, I don't think it's that big a deal either, plus a chance to check things out more carefully--valve cover gaskets, oil vapor system, intake multistage vacuum system (prone to gumming up over time), etc. From my C5 4.2 experience, issues will likely be found among this stuff as car gets to 100K. Having pulled my W12 intake recently to get to the spark plugs, it was also easy--maybe more so than my C5 4.2 at the margin.
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Old 06-17-2014, 09:10 AM   #9
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Thanks for the reply, MP. I decided to quit being such a whiny baby and ordered the gaskets yesterday, but your reply bolsters my confidence. I'll probably give it a go without removing it first just to see; got the set of three O2 sensor wrenches on loan from O'Reilly's.
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Old 06-17-2014, 10:18 AM   #10
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Gabor did mine at the transmission shop years ago, I stood and watched him. He used the big black crowsfoot one, I think it might be a harbor freight tool.
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Old 06-28-2014, 05:44 PM   #11
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I did the pre-cat O2's on my D3 and you have to take the intake manifold off. I attached the Elsawin how to below!

You definitely need the O2 sensor socket as you have to thread the wire through it. I also had to use black tape to hold the sensor in the socket while I started it by hand.

D3 A8 Pre-Cat O2 Sensors ELSAWIN Tech Writeup
https://drive.google.com/file/d/0B06...it?usp=sharing
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Old 07-06-2014, 07:21 PM   #12
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Quote:
Originally Posted by PaulW View Post
Gabor did mine at the transmission shop years ago, I stood and watched him. He used the big black crowsfoot one, I think it might be a harbor freight tool.
Paul, thank you for helping people on AW for over ten years.

As I searched I found a great response from you - in 2003!

I wondered 1) is the Ross-Tech test you mention a test-run of the valve(s), the pump, or both. And (2) how do I do it.

I have tried to blow through the pipe ( by mouth, as Bentley implies) and it's sealed. I think I replaced the vacuum hoses to those valves but maybe I'm confusing them with the EGR valves... it's late, and I'm tired.

Muchass Grassyass!
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Old 07-06-2014, 07:26 PM   #13
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Quote:
Originally Posted by rn3037 View Post
I did the pre-cat O2's on my D3 and you have to take the intake manifold off. I attached the Elsawin how to below!...
RN Thanks for that excellent doc. It's almost identical to Bentley, FWIW. Yeah, if the wire goes under the manifold it'd be problematic - at best - to do without manifold removal.
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Old 04-15-2015, 08:04 AM   #14
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My car threw code P0135 yesterday for Bank 1 Sensor 1. It is a 2005 D3 US SWB, 102kMiles. I just moved from San Diego to Seattle and I guess the sensor feels like myself, it is just too freaking cold here.
Anyway, I plan to replace both and checked the part price on Rockauto, Bosch part sells for about $100 each. Local shop wants to charge $260 for each sensor which I consider too much of a markup, that is just my opinion.
Assuming that the manifold gasket has to be replaced along with the sensors and ties and nothing else comes up, what would you think is a fair price for the entire job including parts? I am asking now before shopping for a more reasonable independent repair shop.
Thanks.
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Old 04-15-2015, 04:29 PM   #15
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Not that I am 100% correct here, isn't B1S1 the front sensor on the rear most cat on the right side? At least I believe it is on the V10.
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Old 04-15-2015, 05:26 PM   #16
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Quote:
Originally Posted by AdilY View Post
My car threw code P0135 yesterday for Bank 1 Sensor 1. It is a 2005 D3 US SWB, 102kMiles. I just moved from San Diego to Seattle and I guess the sensor feels like myself, it is just too freaking cold here.
Anyway, I plan to replace both and checked the part price on Rockauto, Bosch part sells for about $100 each. Local shop wants to charge $260 for each sensor which I consider too much of a markup, that is just my opinion.
Assuming that the manifold gasket has to be replaced along with the sensors and ties and nothing else comes up, what would you think is a fair price for the entire job including parts? I am asking now before shopping for a more reasonable independent repair shop.
Thanks.
Take the cheap parts there and watch the labor rate jump. He has to eat too. Only way lower cost parts work is when you do the work yourself.
Also note that non-Audi Bosch sensors may have different cable lengths making the installation somewhat messy. This happened to me on a VW Beetle.
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Old 04-15-2015, 06:34 PM   #17
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Default You can get identical in Bosch

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Originally Posted by Mister Bally View Post
Take the cheap parts there and watch the labor rate jump. He has to eat too. Only way lower cost parts work is when you do the work yourself.
Also note that non-Audi Bosch sensors may have different cable lengths making the installation somewhat messy. This happened to me on a VW Beetle.
You just have to know how to read the (end of the) many digit Bosch number that is on the Audi OE sensors and convert it to the 5 digit short form used for the Bosch ones you can buy on Amazon, autohauosaz.com, etc. BTDT on the W12; cost 40% or less of discounted dealer. Exactly the correct lengths and correctly color coded at the plugs. 100% OES, just a bunch less $. Actually can still get a specific length one via Bosch that Audi superseded into a lesser number of "one size fits several"[not really well] that they apparently installed in post 2006 W12's on the drivers side.
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Current #2: 2013 Q5 2.0T hybrid; Scuba blue w/ chestnut sport interior; Euro delivery 7/2013 (pictured at Ingolstadt); RS5 front brakes
Prior (each modded): 2000 C5 A6 4.2 & '96 C4 A6 2.8Q, both still w/ family; '85 C3 5000S 5 sp FWD; '73 C1 100LS

helpful cross reference to a C6 post with MMI and other TSB's that also cover D3 A8's.

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Old 04-15-2015, 06:39 PM   #18
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Default B1S1

Quote:
Originally Posted by 1Wasserwerks View Post
Not that I am 100% correct here, isn't B1S1 the front sensor on the rear most cat on the right side? At least I believe it is on the V10.
B1S1 should be forward sensor, forward part of motor, U.S. passenger side on a W12 or S8. B2S1 would be same side but the rear cylinders. Gets confusing on trying to map these from the V10 and W12 to V8 though. On V8, B1S1 would be the whole U.S. passenger side, and then B2S1 jumps all the way over to the drivers side (which would be B3 and 4 on the bigger motors). S1 sensors are alway the forward position ("pre cat") ones.
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Current #1: '06 D3 A8L W12 brilliant black w/ amaretto; 4 seat setup, CPO; modestly lowered, H&R 20mm rear and 12mm front DRs with 275/35 on OEM polished + forged 20's; S8 sway bars (see: rear bar and gen'l D3 bar info and front bar); tweaked 385mm front factory brake mod and matching rear brake mod; matching C6 A6 back headrests (better rear view: headrest tweak); owner installed AMI retrofit with part number details here. [pics now only in picture poster] Upper control arm reference (+ more info in replies) here. Lower cost D3 OES sway bar links here.
Current #2: 2013 Q5 2.0T hybrid; Scuba blue w/ chestnut sport interior; Euro delivery 7/2013 (pictured at Ingolstadt); RS5 front brakes
Prior (each modded): 2000 C5 A6 4.2 & '96 C4 A6 2.8Q, both still w/ family; '85 C3 5000S 5 sp FWD; '73 C1 100LS

helpful cross reference to a C6 post with MMI and other TSB's that also cover D3 A8's.

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Old 04-16-2015, 04:39 AM   #19
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In this picture (not mine) it shows B1 (yes for the front 3 cylinders) but the cat is located rear-most from the engine. The connection for these sensors are located under the rear-most part of the belly pan area.
Yes you can also go to the Bosch website to find the number for replacement oxygen sensors. I think also cross-reference to a vw beetle, somewhere in the $80-90 range.
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Has Anyone Replaced pre-cat Lambda (Oxygen) Sensor Without Removing Manifold?-screenshot_2015-04-16-08-24-28-1.jpg  
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Old 04-16-2015, 07:26 AM   #20
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Quote:
Originally Posted by 1Wasserwerks View Post
In this picture (not mine) it shows B1 (yes for the front 3 cylinders) but the cat is located rear-most from the engine. The connection for these sensors are located under the rear-most part of the belly pan area.
Yes you can also go to the Bosch website to find the number for replacement oxygen sensors. I think also cross-reference to a vw beetle, somewhere in the $80-90 range.
Thanks, interesting what Audi had to do to get those 10-cylinders past US EPA *****!

In that cross-reference are the wire lengths & connectors the same? Curious, not argumentative. I've personally used the "generic" Bosch lambda sensors without any trouble many times. I think the key is weather proof crimp terminals - they have built-in shrink tubing (i.e., the plastic part of the terminal shrinks to become one with its mate) covered with another layer of heat shrink tubing. Just bought
a pack of these; they actually solder and shrink simultaneously a pack of these; they actually solder and shrink simultaneously
with a heat gun or a crack torch (I have one in my "road" toolbox for soldering and shrink tubing)! Great reviews but kinda pricey. Have not tried one yet.
Click the image to open in full size.



I've been crossing Bosch parts for my Alfa since (pre-internet!) 1989... The dealer would give an Alfa/Ferrari P/N and it'd be, say, $250. There was a tiny Bosch authorized shop down the road and he'd cross them over to the "root" Bosch number and it'd be $50.
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