Catalytic converter
 

How many of you had to change you catalytic converter on your X? How many miles did you have when you had to change it? I got a fault and it reads catalytic converter below normal operation... I am assuming its plugging up. But I also have bank 1 & 2 oxygen sensor falt. Planning to change sensors first. Best place to buy sensors?

I find these guys sell O2 sensors at a very competitive price.
I bought from them 2 times,although after a year my after catalytic O2s are aging(may be the same cause as you describe)

BMW Oxygen Sensor Rear - Bosch 15109 | FCP Euro

Thanks for the link... any special tool required to swap these out? Looking at the sensors, it doesn't seem too hard? The front and rear bank sensor seem to be the same. Is the after the cat sensor different part number.. checked realoem, have a hard time finding it.

I see that you have a 3.0i model and I see,that in the description it should fit your model as well,but the pre and after sensors are different.Longer cable is the indicator as well.
As of a tool,there's a special socket with a cut for a wire to pass through.
Also it should be heated before removal.

If you are not going to reuse the old 02 sensor, just cut the wire and use a normal deep socket to remove it. Before putting in the new 02 sensor, attach a compression gauge (the thread on the 02 bung is the same as for spark plugs) pre cat and read the back pressure with the engine running. The back pressure should be 0 but no more then 2 psi. If the pressure is more then 2 psi, your exhaust system is clogged.

A new 02 sensor can be installed with an open end wrench so there is no need to buy the "special tool".

I rent the O2 sennsor sockets set from AutoZone for free. Just pay the full price deposit of $30. They will refund it when you return them.

Awesome feedback guys.... Is a compression gauge something I can rent 2? I will check with autozone

Yes autozone will rent you a compression gauge.

Here's a youtube on using the compression gauge to test for a clogged exhaust system.

https://www.youtube.com/watch?v=9TlygJMxTps

I use a 22mm wrench and it fits prefectly. I also have the 7/8" O2 socket but I dont like it. It flexes and it seems like it would or could strip it. I use the closed end on my wrench and i use another wrench on the end for extra leverage. Also check out Discount Auto Parts Online -- PartsGeek.com - Domestic & Import Auto Parts Warehouse they seem to have everything for my hard to find 4.8is. Goodluck

Wanted to chime in. My neighbor had a similar issue on 1 bank. Replacing the pre-o2's didn't do the trick. The OEM cats are very expensive as you know. I did find that RMEuropean carried an OEM reman unit for about half the price. I installed it for him and it has worked perfectly. Apparently you X guys are more prone to cat issues for some reason.