I never suggested he just start throwing parts at it. I suggested he used the combined information from others in the meantime since he's posting on the forums. I don't know where how he's getting his information since I don't know who his mechanic is...see #2 below.

1)Fuel quality can be changed in one tank - so maybe he should switch.
2)He says he has a mechanic, but didn't state if its the stealership, an indy or some guy doing it from his home. Maybe he'll chime in as to who's doing the work and/or if he's had the software update, if his X even needs it still.
3)He's already replaced 3 of them, so hopefully that's not the issue.
4)Im guessing the stealership cats are well over $800, but I don't know about their specific pricing in the 3.0's. I remember 5/7 guys getting quotes will into the $2k range. I know you don't approve, but I've had absolutely no problems w/ my Magnaflow universals. Some have, some haven't...but I still blame it installation errors more than poor quality since some people still get efficiency codes after a fresh installation.

Hi Guys,

Thanks for your continued interest in solving my problem. To answer some of the questions posed:

I get gas at 4 or 5 different stations, so I think fuel quality can be ruled out.

I've searched this forum pretty thoroughly, as well as the other sources I can find on the net. I've not come across this particular code & problem set in all my searching. Although this is my first post on Xoutpost, I've been a member for a couple of years (going back to the X5world days), and have found the info here very helpful for things like window regulator fixes, CV boot replacement, and the like. I'm a regular poster/reader over on FerrariChat, where they also chastise folks for not searching prior to posting a question, so I'm sensitive to that.;)

I bought my X5 new and its been maintained by the dealer. Over the last couple years I started doing the oil changes and fixing little things that go wrong myself because: 1. I enjoy working on it. 2. I've come to HATE the dealership repair experience. In my opinion, these guys are simply parts changers only interested in squeezing every last dollar they can out of you (although I do agree that sometimes you just have to bite the bullet--maybe this is one of those times).

I'm to the point that I only take my X5 to a mechanic if I can't solve the problem myself (like this one). The mechanic I've recently tried is a highly recommended BMW/Porsche/MB indy. He seems pretty sharp to me. He doesn't have the BMW scanner, so he can't be certain of the solution either. He is however fairly certain that it is not a bad cat because it isn't displaying any of the usual signs of a cat failing.

I also think a very salient point is that the same code comes up with the plug connections swapped between the two post cat O2 sensors. If the post cat O2 sensor was throwing this code, the computer would see them as swapped and then read the front bank as too lean, but it doesn't do that, it still throws rear bank too lean. Do you see what I mean? So I'm leaning to something in the computer.

I'm interested in the DME software update noted. Is this something the dealer would do in the regular coarse of maintenance, or only if there were a problem. Do you know if there's a TSB out on this?

Hope this post provides the needed additional info.

Thanks again for your help.

Honestly it looks like you were changing parts as well. Hypocrite? But sometimes you have to install a known good component. So don't knock the person that throws a part at the car when you'd do the same. There is a simple test to check the cat. Purchase an Oscope and set measurement to 0-1v measure the voltage of the post cat, a low reading indicates that the catalyst cannot hold oxygen effieciently and must be replaced. Compare the readings to the other bank.

I think the difference is that I don't claim to be a professional mechanic.

Thanks for your help.

Killcrap, what's your deal lately man? You criticize me for telling people to get off their ass in my own, honest way by telling them to use search if I know it's out there...but your assuming and just going straight to biting people's heads off.

Hey eracer61, make sure to put on your flamesuit if you have a question in regards to the fuel filter service intervals...he's over there assuming and biting too. In the meantime, use search and hopefully you get an answer to your problem. Make sure to post your findings so other can benefit...when they use search. ;)

Any luck eracer?