N_Jay

Have not had a chance to check yet, but thinking the tow company snagged the wire to the O2 sensor.
Which side is bank 2.

clancy

In US driver's side is bank 2.

N_Jay

Thanks.
Hoping for a simple wire repair.
At first I figured the CEL was just from all the screwing around with the battery since the accident, but after we cleared the code both came back right away.
Both are (or can be) caused by an open circuit, so that is why I am suspecting the wiring.
The car had been on and off a flat bed at least twice sine the accident.

N_Jay

Can anyone confirm hat secondary O2 sensors are just to measure cat efficiency and the mixture is set by the front sensor?

tester123

perhaps the other way...

From Repair manual:

• Oxygen sensor control after the catalytic converter is responsible for final control correction. It is the primary sensor and can override the signal from the oxygen sensor control before the catalytic converter.
  
• It corrects slight changes in the mixture (for example enrichment) via the oxygen sensor before catalytic converter by holding the oxygen sensor control before catalytic converter at its higher or lower limit for a specific time (duration). If this time is in the positive range (for example 50 ms), mixture is shifted in the -enrich- direction. If this time is in the negative range (for example -50 ms), mixture is shifted in the -lean- direction.

N_Jay

Interesting. Darn.
Well, with the failed sensor (or wiring) I still have decent mpg, so it can't be too rich.

jcman

Although the post sensors do adjust trim it is on a "long term range" only and not on open loop, this is considering that the catalytic convertor signals are in the range of working with a smooth wave compared to the choppy pre sensor wave, the post sensors primary role are to report cat status and not instant fuel trim adjustments as the pre sensors do so if the cats are outside of efficiency the post sensors lose the fuel trim role....and you get a slew of CEL codes.

Audi OBD2 ECU's going back to the M5 4.2 incorporated the 3-way cat systems used on our ME 7's with really no change on this monitoring system.

What repair manual are you getting your info from?

tester123

What they are saying Kinda makes though. Post cats is where to look to determine the final output (to maximize efficiencies, reduce emissions and all...) thus, post cats can in turn control (trim/adjust etc.) the mix (just as they say). The way I understand it is that pre-cat sensors provide the primary feedback of mixture where post-cat sensors can control/adjust the pre-cat sensors' signals to further adjust the mix... if it makes any sense .

I found this info in ElsaWin. Also checked Bentley as well (of course they copy line to line from factory manuals). Both say the same thing. FYI, I am checking this info based on my car yr/model.

N_Jay

The engineer in me assumed the first sensor has the best info as to the O2 in the exhaust flow (Much like a single sensor system) and then assumed the second sensor mostly read Cat efficiency for compliance reasons , and not for tune.


A am sure I was not rich enough for the 600 mile drive yesterday to hurt the cats, and it will not get many more warm up cycles before all is fixed.

And one else see rear sensor or rear sensor wiring problems after a tow? (Haven't go under it yet)

tester123

Personally, I haven't seen any wiring related to O2s get mangled during a tow. However, I did see one jack *** trying to hook the axles to pull the car onto the flatbed. Thank GOD I was there before the idiot actually pulled it and rip the boots etc.

Did you check for codes? Not sure if it would help... but O2 sensors can be monitored by VAG-COM (did this a long time ago do not remember that actual procedure) check the manual