When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Hi, just bought a 2015 A8L 4.0 TFSI, on my way home I got the following faults. Car has about 190 000 km and run fine the whole trip to home - 700 km and still does I plan to replace both rear oxygen sensor and if the faults persist - remove the converters and install downpipes (rear sensors will have to be deleted). Just wondering if 190 000 km is not too early for the converters to go bad? Mixture adaptations are perfect, car runs as it should, as I said. PS: car throws codes after driving about 100 km and not right away.
Better search before you throw parts at it... Low chance it is the converters...AND it may not be the sensor you are thinking either. Remember, always question whether the telemetry (sensors) are correct.
My best guess: counterintuitively, it is your FRONT sensor on the Bank 1 side that is going bad, even though code is pointing to rear one. Basically if the front sensor misreads (fails) and then starts seeing a false mixture, rear sensor data gets confused in ECU. ECU thinks the front sensor is reading richer than reality, and when it sees the rear sensor data, it then wonders why it (falsely) appears lean. Hence the rear sensor fake out code. Rear sensors can fail, but fronts are the much more likely.
Your report is very similar to mine. I suspect when it generates the error it is either with very long steady driving, or at some point when the cylinder on demand (COD) system cuts back to 4 cylinder operation.
BTW, if you change either both fronts as a pair, or alternately both rears as a pair, one will be fairly easy and one really difficult. One front O2 connector is grouped with the OPPOSITE bank rear with the connectors easily accessed under the hood/bonnet, while the other group of connectors is very awkwardly positioned above the USA/Continental Europe passenger side inner CV joint. You'll understand if you look at the converter area under the intake decorative cover in back how the converters are essentially tied in an exhaust knot, and how in order to run the wiring to the sensors without touching the hot surfaces why they did what they did design wise. The sensor end is easily accessed at upper rear of engine under the engine trim cover, and a lot easier than many older Audis buried underneath. It is the plug end that is difficult for one each of the fronts and rears. I prefer to use the pre wired sensors in Bosch (who is the OES). But if it is in the hard to reach connector set, you might opt for the splice in type. I just use ramps for underneath work. With a lift, the hard to get at connectors would be easier, but you still have to do the connector disconnect and removal from attachment/tie down points by quasi blind feel. It's really awkward where it is, bounded by frame rail, CV joint area and suspension stuff. The other connector set under hood is child's play by comparison.
I do not believe it is a cat converter fail.
I had the same code come up at the dealer when I bought my car and got them to check it over. They were going to just replace the 02 sensor but I said I would do it myself. I cleared the code to see if it would come back and it did not come back for 6 months. When it came back I decided to only use premium fuel and it has not come back again. If it does come back I will clear the code and change the sensor in summer when it is not so cold.
01-07-2024, 10:44 PM
4.0 TFSI catalytic converters fail?
I plan to replace both rear oxygen sensor and if the faults persist - remove the converters and install downpipes (rear sensors will have to be deleted). Just wondering if 190 000 km is not too early for the converters to go bad? Mixture adaptations are perfect, car runs as it should, as I said. PS: car throws codes after driving about 100 km and not right away.
