MP4.2+6.0

So, your part # is correct in position B1S1, but it is the "newer" Audi OE number. The newer number is 1K0998262J in that position. The older # is 03C906262B. I pulled an "old #" one out of my W12, plus I got the dealer (Audi USA Parts/Sunset) to confirm all those numbers at the VIN level. The entire cable portion of 03C906262B is just about 7 ¼ inches, which matches up virtually exactly with the Bosch 17177 I installed. All 4 sensors had the part numbers superseded BTW, so it's not something special about this sensor--I think Audi just did some part # rationalizing.

Also, if you look at your Audi one that you took out, it should have a manufacturing date on the first line, right after VW AG. My old one is 3/05, which makes sense for my car build date which was a month or so later. If your sensor manufacturing date is after your build date (on the sticker near the drivers door hinge area), it's a dead give away the part was changed. Same for any part on the car more generally since Audi parts usually have a manufacturing date stamp. If you have a later car build date than me (mine was quite early as a 2006), you may have had one of the post part # change sensors.

Meanwhile sensor #'s aside, I'm not really sure about "signal too low" in a wiring context, but that text description is sounding more like now it just says you are lean in cylinders 1-3. That leads to the usual check for vacuum leaks, which on the passenger side after the MAF can't be much other than the rubber boot from the air box to the intake--the pain in the butt air boot clamp that is on the MAF side--so I would recheck that spring clamp plus the screw clamp end. Meanwhile, I would also run some Techron gas treatment thru if you haven't done that lately, in case one of your 1-3 injectors are a bit fouled. After that, guesses could be a leaky injector o ring seal somewhere in positions 1-3, or a deteriorating MAF. MAF's logically should be across to the rear bank too, so some similar lean codes there; arguably the same for the rubber boot the right side intake gasket (at the split point/seam) type scenarios too.

One last wiring related check maybe on the pre-cat O2's on that side is to be sure the plugs weren't switched--they both end up in that auxiliary plastic bracket below where the other ones are higher up around the air box rear side. The front B1S1 is black on both sides of the connection (including the Bosch replacement), while the one for cylinders 4-6 should be brown on both portions (at least if it still has the factory sensor). If something has ended up crossing from brown to black on the same connection point, presumably they got reversed. Hopefully that's in order though.

MP4.2+6.0

S1's are pre, S2's are post. B1 is cyl. 1-3, B2 is cyl. 4-6 on W12's.

03_AR_CO

Well alright, I disassembled everything one more time. Removed the airbox, and removed the intake pipe just to inspect. I found everything to be in good order, my B1S1 O2 sensor is plugged into the correct harness connector, black connector under the intake pipe. In VCDS I cleared the codes but did not put enough time or miles to get it to either accept or fail the readiness test. I did however do a stare and compare in the measuring blocks and B1S1 was behaving the same as B2S1 with all of the relevant voltages and adaption values. So I am hopeful putting things together one more time may have done the trick.

Here is the kicker though, while driving my suspension cease and desist amber light illuminated and I pulled back into the garage to find that I have a leak in the passenger side air spring, and my pump has been working overtime. So the W12 is parked and will remain so until the ordered parts arrive.

Since my control arms are in need of replacement, I am replacing both front springs, as well as the pump. I can tell by the racket the pump is making that it is getting tired too.

So the O2 sensor work is on hold until the car is drivable again. MP4.2+6.0 thanks for all of your help in this matter. I will post up my findings once they are available to me.

Also if anyone can link me to a decent writeup on front bumper removal, so I can get at my suspension pump many thanks in advance.

03_AR_CO

Well after a long weekend of wrenching, I have the W12 back on the road. Removing the air box and O2 connectors, examining the ECU cabling, dislodging and re-seating that connector as well and putting things back together must have cured my O2 sensor blues. I have about 250 miles on the car since clearing the codes last, and I have no check engine light, and the readiness self test shows as passed for the O2 sensors. So all appears to be fair with the universe finally. An additional note, the car seems even more responsive now, I had been experiencing some minor lag ..... that is gone.

The other part of the weekend efforts was all the suspension items. The most tedious part of the job would have been replacing the suspension pump. The W12 has the pump in a position that requires the bumper to be removed, and the lock carrier placed in service mode so that you can get at the bracket mount bolts. Very tight in that space to get at and remove, unlike my 4.2 which I found much easier. Additionally I found out that the pump brackets are not the same as the 4.2 model air pumps, so I had to remove the bracketing from my old pump and install it on the new pump which required some drilling and riveting, an unexpected PIA. I ended up replacing all 4 upper control arms, two lower front arms, sway bar links and both front air bags. I had some anxiety before doing the suspension work but it was easier than I had anticipated. From doing this work, no one should be afraid of replacing those air struts themselves. I found them to be easier to remove than the allroad air springs.

Once again the car is tracking great, no suspension creaking and groaning, air struts are holding air, change ride height in short order, no check engine lights and great acceleration once again. What an amazing ride these cars are. MP4.2+6.0 and all others who helped, thanks for helping me solve this one ....... very much appreciated.

nathanwind

Cross post, but having a similar issue to the OP with the P2195 CEL code. Tried the approach used here of taking out and inspecting airbox, but so far no luck.

Here's my thread:
https://www.audiworld.com/forums/a8-.../#post24655610

volvopentaman

To note on W12 (and V10 models), there are actually TWO of each sensor.

Both W12 and V10 have two ECM:s, J623 (Master) for passenger side bank, and slave (don't remember the "J" number now) for the driver side bank.

Both banks have of course B1S1(precat front), B1S2(postcat front), B2S1(precat rear) and B2S2(postcat rear).

You have a readout in the first post from adress 01 (=general OBD ECM), this doesn't tell from which ECM the code pops, master or slave.

In the "adress word" label master = 10 and slave =11, if the address label is 01 as your first post, it's a general OBD reading from both ECM:s together, and can't distinguish which ECM the code is from.

I had the "lean" code on my ex 2006 W12 B1S1 (the sensor was just replaced i could notice from the MFG date)

Stealership had repaired the sensor wiring to the ECM side with a "pigtail" they'd just crimped on.

Removed the pigtail parts, cut off a few centimeters to snuggly fit new connector "souls" (the metal parts) onto the cables, and plugged back in, and worked like a charm for 40.000km.

MP4.2+6.0

per the other post string I don't think it is an O2 or its wiring. But agreed with what you are saying if sensor and bank specific. The is a TSB for the W12 O2 sensors through 2005's. I found a connector issue on one of my 2006 (pre cat) ones as well. New connector end and new terminals with it and issue fully resolved.