scout2

Went to do this to get rid of the CEL. 2004 - 2.7t

I am confused by the terminology (found a few posts about it that reiterate this confusion). I found the "post" cat O2 sensor on top and in the "front" of the catalytic converter underneath the car. I thought I was looking for something after the cat and routing of the wire looked incredibly difficult. So I put it off until I could post a question.


1. is the: P0036: HO2S Heater Control Circuit (Bank 1 Sensor 2) P0141: O2 Sensor Heater Circuit (Bank 1 Sensor 2) actually in front and on top of the cat under the car?

If as described, do I cut it on the bottom and attach the plug from the new one to it to fish it up to the engine compartment? Any other install advice?


From another site, but this is what I found: http://www.audiforums.com/forum/atta...n-p1010017.jpg


Thanks in advance!

clancy

That is it. Some people buy a generic sensor, cut the wire near the sensor, and use the existing cable by splicing the new cable onto the original cable near the sensor. Others get the OEM sensor and snake the cable over the trans keeping it away from heat and moving parts. You cannot remove the original cable and use the original fastener locations without removing/lowering the trans. I simply routed the new cable near the old one and hoped for the best. Has lasted a few years thus far. There are many threads on this issue if you search.

scout2

Thank you very much! - I did search, everything seemed to concentrate on the harder front sensors and the post verbiage had me a little confused.

Thanks again!

clancy

Try this thread. https://www.audiworld.com/forums/a6-...2775139/page3/

Bottom line, if using OEM sensor you will need to fish the wire somewhat near the original routing as best you can and tie it such that it is secure and away from danger. It will work. Or, use the original wire and splice.

scout2

Well I finally crawled under there and changed it out - that was fun.

The news is I cleared the code and now it has come back. I will do some reading on "testing" the sensor, if that checks out is it the CAT?

clancy

Did you install OEM with the wires all the way to the plug on the firewall, or did you splice in using the original wiring? I recently replaced one of these B1S2 and used the splice method this time. It came with special connectors that did not require any soldering. The Bosch site actually said that soldering would not work. It would somehow destroy the signal.

Also, have you read about using the spacers or extenders (I forget the correct term) along with the O2 sensor? This device effectively moves the sensor back a bit so it does not get directly into the exhaust stream. This reduces the sampling of exhaust and tricks the computer into being less sensitive. I did this years ago when many on here were telling me to replace my cats. Worked just fine. Have had them on both of our 2.7 cars for a long time. Again, search the archives for a more technical explanation.

scout2

Interesting - I am not aware of the spacers/extenders. Thanks I will search.

I used a bosch sensor that had the same plugs and while a pain to route it - I was able to do that keeping it away from the downpipes. It has what appears to be an extra foot or so of wire, which I just ziptied around the loom mount. I've left the old sensor and plug in place until I figure this out (meaning they're just "hanging out there" - in case I need options. I have the free version of vagcom and will do what I can reading blocks.

Thanks.

N_Jay

The wire routing is around the transmission and from what I understand requires dropping the trans to replicate.

georgeb944

No, it is not the cat in this case.

The heating circuit is designed to "preheat" the sensor so that it begins to report the levels of oxygen earlier than it would if it were to rely on the heat of the exhaust stream alone.

This code says that there is no connection between the two legs of the heater circuit (a simple resistance test will confirm it) and needs to be repaired or replaced.

That said, on my first C5 2.7T car, the mechanic had replaced all the sensors and the catalytic converters and the CEL still glowed. After diagnosing with a VCDS, and an ohmmeter, I concluded that, while the sensor wiring was good, the ECU was converting the good result to a bad reading and setting the CEL. A new ECU fixed the problem.