I would trace the charge air lines from the turbos back to the intake manifold. Sounds like something is disconnected. Probably nothing big in my opinion. Good luck.

So got my car back today. Turns out the MAP sensor failed. I got the part back and it was pretty gunked up. Car runs great again with no more codes! :thumbup:

Nice find! How did the mechanic single this one out?

So good to hear that you got it all figured out.

For interest, check out this post - similar issue. Interesting that your code numbers were quite different, but both yours and in the link I just referenced deal with "charge pressure." Also, in both cases the problems were solved with replacement or cleaning of the MAP (Manifold Absolute Pressure) sensor.

So obviously my thoughts about the EGR/throttle valve being the source of the problem were wrong - sorry! Not sure whether the MAP failure was due to CBU, or failure due to another mechanism. If you were really a Curious George, you could clean the old MAP sensor and see if it still worked! Nah - too much work, and things are all good now!

Thanks for posting the resolution of this problem - very helpful.

Wish I knew! I was expecting much worse to be honest. New MAP sensor was $80 plus 2 hours of labor. Not bad at all.

Well going forward I am still a bit concerned about CBU. I talked to my mechanic about it...he suggested that we not worry about it until it becomes an issue. When I have time this fall I definitely want to do an inspection of the EGR/throttle valve. Perhaps a new thermostat is in order too?

I had to replace mine yesterday as well, about 77k miles on my X5. I was able to just lift the air box and get my hand under to unclip the harness and pull the sensor without having to remove the airbox completely.

It helps if you've removed the water trapping sound insulation that covers the intake manifold too

I contemplated on leaving this foam off but put it back in.
What are your thoughts on this, what difference in noise has this made? I was afraid of getting too much noise in the cabin if i removed it.

I suggest you see this thread and them make up your mind

Error code 4B99 and 483D - Bimmerfest - BMW Forums

Looks like ill be removing that dirty thing thins weekend and check for the corrosion issue.