gerisilo

I have a A4 3.0L and I have replaced the driver side pre cat O2 sensor twice within a couple months of each other, with OEM O2 sensors, and each time I am still getting a slow response code for that sensor.

I took it to a shop for diagnostics and they ran each O2 sensor to get their exact readings, and they said they all start up fine, but the driver side pre cat sensor gradually gets slower and slower. They were stumped and not sure what the reason might be.

The car is still running fine, not idling rough or running rich, but the CEL is eternally on. Thinking about selling the Audi too, so it would be nice to have the CEL off.

Any thoughts? Would be awesome to figure this out once and for all.

turbo510

I would wonder about the cat on that side, if somewhat clogged might slow the exhaust flow. Maybe a few good full-throttle runs up a long hill would help. How does it run otherwise?

NYC_S

Hi, did you replace the sensor yourself? What was your trick on getting it out. If you brought it to the shop, how much did they charge you for it.

gerisilo

I wondered about the cat as well, but the shop said that would be throwing a separate code, especially since the sensors are so sensitive.

I did change it myself. Just used an O2 sensor socket and a long extension to a ratchet. It's kinda awkward but easy enought to do. The shops usually want to charge 3.5 hours of labor. It took me maybe 30 minutes. Just make sure the engine is completely cool, it's a lot easier if you can get your hands in and around there without burning the crap out of yourself.