Hi. New to the forum. Own a 2001 Audi TT roadster Quattro. Recently, CEL came on and code was P0138 and that was the only code. Was told it pointed to the downstream O2 sensor. 2001 are strange as the O2 sensors changed mid year and last 6 of my vin is 037243. I was told that the difference in bosch sensors is mostly length of the wire and purchased Bosch model #16978.

Installed it and the P0138 code is gone but it now has code P0422. There was a bit of corrosion on one of the connection plugs under the cover and a bit of moisture... cleaned that with electronic cleaner and let things air dry for a bit when I installed the new sensor. The P0422 seems to point to the Cat but it was fine before and ONLY thing replaced was that O2 sensor. I have searched quite a bit but seems to get me more and more confused at this point.

Question is: Is this code now present because I didn't use the exact plug specified. I fully admit I am new to Audi's and may be missing something here. Should I purchase a new plug or possibly also replace the upstream sensor.

Long post for a first one I realize...trying to condense it down as much as possible. Car has 100k on it.

Any and all help will be much appreciated and looking forward to being active on the forum.

 

Lots of views but no opinions or advice. Maybe I am the only one who has had this issue so I will try to do further investigating and post if I get a solution to help the next person who may run into the same situation.

 

Hi there!

I guess I have a.) some insight on these sensitive beasts b.) some Qs for you c.) some Qs for the forum to help us out.
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I just battled (am battling) a similar O2 thing, but on the ATC engine (just posted a thread above:
https://www.audiforums.com/forum/aud...uccess-221808/
requesting alternate part #s).

Basically, this thing (@ least my '01q ATC; not yours) is extra sensitive to O2s. I am trying to determine if Audi/VW genuine is necessary or varies whatsoever from OEM Bosch (it shouldn't but these problems are happening..). You were right so far, at least, in not going with a non-OEM part, since I've tried and failed horribly; as in, even when I got a few minutes or days with the CEL off after battery or VAG/OBD reset, it will not exert its power. It was bad when a sh*t O2 was in there, and just terrible after that sh*t O2 stopped throwing any voltage: As in linear, wouldn't-even-know-it's-a-turbo-if-you-couldn't-hear-it power; stockish HP despite it being stage 1++; etc. It seemed to signal some BS that messes with fuel, and doesn't allow it to run right. Which sounds illogical & ridiculous per 99% of other cars' downstream/secondary O2s, but you are probably learning this German wonder is quite special Might not mirror your problem, but I'm trying to show how I've recently learned how sensitive the damn downstream O2 is.
While we're on it, *ONLY* go with a genuine CTS (coolant temp sensor) if you've yet to upgrade it. Also, the MAF can be goofy or bad without throwing codes, so can check and clean that as well if it's running poorly or awkwardly. Disconnecting mine in a recent [short] interim cured a thought-to-be-incurable hiccup after fixing a massive vac leak and confirming perfect boost, tune, and multiple other things.


Another thing I've sadly realized, at least with these older ones (or @least mine), is the necessity to reset the ECU with VAG ... NOT a battery reset, 450+ ignition cycles, or ODBII scanner. It does not recognize when I replace a part until I reset it. ie, my *new* CTS continued to act up & throw its code(s) until I reset it with the software. That also went for aligning my TB (throttle body) after I took it off to clean, and aligning my headlights, that decided to shoot to the ground one day after working on it, nowhere near them (haha). I have read many different scenarios on sensitivity of people's TTs & CELs, small optimization tweak response, etcx100.

ANYWAY, re: your code: I *believe* (someone please correct if inaccurate) the cat code is p0420; p0422 should just typically point directly to the downstream sensor (like p0138). You don't have any codes for the upstream sensor, right?

Not sure if this will give any insight:
http://www.audizine.com/forum/showth...to-do-about-it

Oh & I am assuming you still have the AMU engine since it's a '01 roadster quattro (wasn't replaced @any point with a BEA); can you confirm? (Significance to that question here = before messing with the upstream O2 someday [CTRL+F "wideband"]:
http://audittmk1.blogspot.com/2009/0...gine-info.html)

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So, I'd re-check its wiring/connection, link up with someone with VAG-COM access to first run a full scan; then read the O2 voltage, see how y'all feel about it, and reset.


--How is your car running?
--Did you happen to purchase it with the p0138 already present?
--Stock cat?
--Did p0422 come on *immediately* after you replaced it?
--Any other codes?

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I'd also like the forum's insight on whether the length of the wire is the only variable across these different VW/Audi or Bosch sensor #s (eg, 1K0998262 vs 1K0998262A; 16978 vs 06A906262BB). AND very much insight on if anyone noted a variance with Bosch vs genuine, or if they are consistent with y'all & truly coming out of the same batch with different branding.

And, in line with this and my similar thread linked above, alternate VW part #s you might have had success with

-t