I have the 02 sensors on order but holding off on ordering the CAT at this point. My thinking is my Oil Separator froze up 2 years ago and "slightly" hydro-locked the motor, but I was able to start her up after a couple of hours of being parked in the garage. Unfortunately, upon startup, the neighbors called the fire department as they thought my X5 was on fire! I'm thinking this caused the exhaust system to "oil up" and shortly after having the oil separator replaced, the SES light came on, and I bet the 02 sensors have never recovered. The CAT does not rattle or make any noise at all, so I'm starting with the 02 sensors on bank 2 and if this does not fix the problem, I'm ordering a $800 BMW manifold/CAT for Bank 2 and have my Indy do the installation.

As for your other questions/points, for oil changes, I've followed BMW's maintenance "dashboard light" method for the life of the truck, with a few extra oil changes in between. Probably should have kept more on top of that, but hey, 158K miles ain't bad! DVanos hasn't been touched and yes, I plan on replacing the DISA as well. I just need to get her to pass our emissions testing program so I can keep her registered and legal at this point. She's only my winter vehicle, but plan to keep her for a couple more years and can't sell her anyway with the SES light on as nobody would buy it in that condition.

It's unfortunate I'm having to deal with this as this X5 is in nearly pristine condition, never been crashed and doesn't even have a door ding after 15 years of ownership. :thumbup:

Everyone complains of emissions codes being so complicated but they're just like every other code in the car, you just have to know how to interpret them and not be afraid of replacing the actual component that the code points to. In this case, the cats.

Great to hear that it fixed your problem, but you don't specify what your problem was? Probably was not a code for catalyst efficiency...

If you think you may have coked your cats with oil and feel that may be causing your code, then you could try a "snake oil" product called CataClean. It might be worth a try. You can't really tap or shake the cat when its in the car to hear a rattle indicating the matrix has broken up... Mine didn't rattle, and it's operating temperature was in line with the other cat in bank 1. In my case, after removing it I discovered that it was COMPLETELY EMPTY. The matrix had long ago broken up and worked its way out the tailpipe.

I don't know if the apps are spot on but my experience is that when there is a problem if there is a +- inaccuracy error it has not been enough to hide the problem.

The closest app to Torque that I know of that is available for an iPhone is Dashcommand.

Where in Texas is your shop?

Preventative maintenance for O2 sensors is around 80,00 miles so probably a good idea to purchase new ones. That said, I would have swapped sensors to see if code moved to the other bank before doing so.

OP, If you need a cat, I have an extra set that I would sell.

I agree with Deansbimmer a cat efficiency typically means a new cat is needed and in order. For the vehicles that we have repaired that generated a cat efficiency code each one needed a new cat.

OK, cool. Thanks for the offer, let's see how this plays-out. Still waiting on the sensors at this point.

*Cringe* :( I hope not, thanks for the info, totally appreciate everyone's help with this!

Have you always run premium fuel (91 octane or above) on the X5 during your ownership?

:banghead: Unfortunately, no. When premium reached nearly $5/Gallon several years ago, we switched to regular gasoline to save about $15 per fill-up and now I have a feeling we're going to get scolded for doing so. In trying to save a few $$$'s, could we have possibly killed the bank 2 CAT and/or 02 sensors?