tx170754

Ok, I've also had an 02 related CEL, the right hand side engine compartment connectors were the culprit, using some tie bands fixed the problem...

PaulW

Thanks....I will inspect those.

MP4.2+6.0

Paul, I think S8 O2 connectors may be less conveniently located/less clustered than W12's, but yes check those. Also if any are broken some on the "car" side of the wiring harness connector, like a broken locking tab, Audi sells just the connector shell if you need it. You just transfer the wired pins over to the new connector housing and insert the plastic retaining clip that is part of the housing. I have now gotten to where I just try to shatter the old connector (pliers and/or utility knife work) intentionally when I do it because of how hard it it to get those individual pins out one by one w/out bending or breaking them. Over the years I have replaced them on a few O2's, and the MAF connectors on the W12 (ham fisted Audi techs...) and my old A6 4.2

You might also look over/trace your O2 connectors against the wiring picture just to make sure somehow they didn't get mixed up. Seems unlikely, but there are so many of them on V10s and W12's, I could see it happening and then either some running or code weirdness at the margin.

PaulW

Just to provide an update, today I went out and unplugged the sensor that I installed last week, started the car, and got the following fault code:

1 Fault Found:

000054 - Oxygen (Lambda) Sensor B1 S2: Heating Circuit
P0036 - 004 - Malfunction / Open Circuit - MIL ON
Freeze Frame:
Fault Status: 11100100
Fault Priority: 0
Fault Frequency: 1
Reset counter: 255
Mileage: 94722 km
Time Indication: 0
Date: 2014.03.01
Time: 11:21:00

Freeze Frame:
RPM: 711 /min
Load: 25.9 %
Speed: 0.0 km/h
Temperature: 45.0°C
Temperature: 15.0°C
Absolute Pres.: 990.0 mbar
Voltage: 13.843 V


Readiness: 0010 0101


I wanted to make sure I replaced the correct sensor, and based on Bank 1, Sensor 2, which appears to be the post cat sensor, i.e. “Sensor 2”.

I would agree with others that only the pre-cat sensor controls fuel trim. I bought an 02 sensor on ebay yesterday:

http://www.ebay.com/itm/160448706817...84.m1439.l2648

The good news it that it was $65, and the better news is that it is really easy to get to. Jack the car up, and then it's on the forward bottom of the exhaust, super simple to get at. Here is a picture from the transmission fluid change (O2 sensor Number 7 on the second image below):




It's still not easy to figure out which O2 sensor is what based on vag-com codes.



Hopefully I will get to change it out next weekend and then see what happens from there.

PaulW

I received my "exact fit" pre-cat Bosch 02 sensor (the VAG part that I ordered was out of stock), the correct one is Bosch 17256. It is truly exact.

Installed it last weekend, and have driven the car since then. For the first time in months I now have an O2 readiness code, and no fault codes.

Prior to resetting the codes, I did have one additional rich code, which I will post here for others, most of the time I would just have the too lean code:

2 Faults Found:

008342 - Post-Catalyst Oxygen (Lambda) Sensor Correction; Bank 1
P2096 - 002 - Too Lean - MIL ON
Freeze Frame:
Fault Status: 11100010
Fault Priority: 0
Fault Frequency: 1
Reset counter: 255
Mileage: 94727 km
Time Indication: 0
Date: 2014.03.01
Time: 13:07:34

Freeze Frame:
RPM: 2335 /min
Load: 28.2 %
Speed: 106.0 km/h
Temperature: 87.0°C
Temperature: 7.0°C
Absolute Pres.: 990.0 mbar
Voltage: 14.224 V

008598 - Oxygen (Lambda) Sensor B1 S1
P2196 - 002 - Signal too High (Rich) - MIL ON
Freeze Frame:
Fault Status: 11100010
Fault Priority: 0
Fault Frequency: 1
Reset counter: 255
Mileage: 94853 km
Time Indication: 0
Date: 2014.03.03
Time: 06:45:10

Freeze Frame:
RPM: 2467 /min
Load: 29.8 %
Speed: 112.0 km/h
Temperature: 88.0°C
Temperature: -11.0°C
Absolute Pres.: 1000.0 mbar
Voltage: 14.224 V



Hopefully this will close the chapter on this fault, if I don't post to this thread again, I'm golden!