Faulty Lambda sensor - location?

[Horrgakx]

I have a fault on a Lambda sensor which is intermittently throwing this error. Looks like it's in Bank 3, S1 (whatever S1 is). Does anyone know where abouts it is, as I'll need to ask the garage to change it.

24416 - Linear Oxygen (Lambda) Sensor B3 S1; Pump Current Wire
P3164 00 [11101000] - Open Circuit
MIL ON - Intermittent - Confirmed - Tested Since Memory Clear
Freeze Frame:
Fault Priority: 2
Fault Frequency: 9
Mileage: 120402 km
Date: 2025.03.11
Time: 16:25:46

Engine speed: 1229.00 /min
Normed load value: 36.9 %
Vehicle speed: 51 km/h
Coolant temperature: 60 C
Intake air temperature: 12 C
Ambient air pressure: 1020 mbar
Voltage terminal 30: 13.853 V
Unlearning counter according OBD: 40
Engine torque: 227.5 Nm
Fuel level: 49.00 l
Intake camshaft B1 active operating state: 1

[steamship]

Both the V12 and W12 are 'split' into 4 banks. Banks 1 and 2 are on the left side of the engine, as you look at it from the front of the car. Banks 3 and 4 are the right side. There are two lambda sensors per bank, labelled 1 and 2. 1 is the pre-cat, and 2 is the post-cat.

With that in mind, B3S1 'should' be sensor G285 (top left) in the attached image. The image is taken from the following SSP on the W12 engine:

SSP490 6.3l W12 FSI engine.pdf

If I was replacing it, I'd first disconnect G286, and go for a very short drive, and then scan the car again. If my numbering is correct, you'd then get an error code for B4S1 (G286). If that was the case, I'd then reconnect it, and replace G285.

[Horrgakx]

Cracking, thanks very much!!

That looks like it might be a challenge to change....?

[steamship]

Originally Posted by Horrgakx

That looks like it might be a challenge to change....?

I think that applies to most things on the W12.

[Horrgakx]

I still haven't bought the replacement yet, mainly because I'm unsure of the part number, it could be any one of the 4 which are pre-cat. So, I asked AI to identify it, and this is what it came back with. Does anyone agree or disagree?

• Based on the information available for the W12 engine, Bank 3 typically corresponds to cylinders 7, 9, and 11.
  Therefore, the part number you need is: 07P906265H (Cylinder 7,9,11) (Grey) In front of catalyst

The plug has a length of wire attached, so it won't be as simple as say, a spark plug, where I could just pull the top connector away as the wire comes as part of the assembly. Is there a way to find out where it goes and what it plugs in to?

[steamship]

B3S1 covers the section of the exhaust highlighted in the attached image. That is on the right side of the engine as you look at it from the front.

The part number you gave is correct for the CTNA engine.

In terms of where the connectors go to, check out the following PDF, starting from page 276. From a quick glance at it, it appears that all the connectors are located under/behind the air box on the right side, which in itself is under a metal brace bar. There is an image on page 32 which shows what all the eight connectors go to.

13-Service Manual 12-cylinder direct petrol injection engine (6 3 ltr 4-valve).pdf

As mentioned previously, once you've located these, I would disconnect plug number 7 (G285), take the car for a drive and rescan. In theory, you should ger a different error for B3S1. If you do, then that is the correct connector, so you just need to follow it to find where it connects to the exhaust.

[Horrgakx]

Thanks, doesn't look too onerous then.
I've emailed the garage to get a labour quote from them. The sensor with wire is £220.

This is a picture of the offending part on the car (I think!!). It's reachable between the right side of the engine and the airbox.


And to put it into context, this is an overview of where it is, just hidden, but where the arrows point;

[steamship]

Seems reasonably easy to get at then. It looks like removal of the airbox is just to get better access to that panel. Pricewise, that's good, as dealer price is £330.

[Horrgakx]

I ordered the Bank 3 Sensor 1 replacement just now [07P906265H G285] and I'll have a go at replacing it myself. I checked this morning and this fault was reported 7 times since I reset the all the DTC's on Tuesday. So I'm pretty sure it needs changed out.
(Weirdly, I reset the DTC's on Tuesday ahead of a 240 mile drive and the car behaved impeccably; no warning lights, no "ACC and Audi Braking Guard not available" message, nothing, for the full journey!).

I found the connectors, they're really easy to reach, they're at the back of the engine, in the centre, under the windscreen. B3S1 sensor plug is the grey one, 7th from the left. Please see photos below.

1) The connectors look like they have a tab which pulls up to release them...?
2) The routing of the wire looks like a nightmare. The wires seem to be fabric wrapped and then disappear into some kind of large tapered rubber grommet.

[HPsauce]

Those look like pretty standard connectors, they're supposed to be easy to release but I always struggle. Hate the things.
You basically press that sort of rectangular cage structure in towards the wiring with your thumb then pull the whole connector up and off. It's a sort of lever pivoted a little way down with a small catch on the other end.
But it can get a bit stuck...

I think if you can somehow press down a bit on the whole connector while pressing on the release catch it frees up more easily. But you then need to maintain sideways pressure to keep the latch open while changing from pressing down to pulling up. Easier than it sounds.

Maybe there's a tool to do it?