[Persian Whisperjet]

Took the car in for dealer service last week (5K left on warranty) with the car showing three codes including two for Nox sensor issues. The codes suggested the "shutdown scenario" described in a BMW service bulletin helpfully posted by another member recently. Shane, my SA, did a great job of communicating the accumulated wisdom of e90post to the techs, who ended up replacing p/n 18-30-5-509-750 (#1 in the diagram below). This is the "engine exhaust pipe/cat."

-- OK, can someone explain what the cat does?

-- Has anyone had this repair and then experienced related failures? Anything to be on the lookout for, in other words?

Thanks in advance for any suggestions. I'm right at the point of having to extend the warranty or ditch some of the troublesome stainless steel baggage my car is carrying around.

[floydarogers]

"Cat" stands for "catalyst". The particular catalytic converter noted (there is another one near the engine in the same canister as the Diesel Particulate Filter DPF, which is termed the "Oxidation Catalytic Converter" in the system used on our cars) is the Selective Catalytic Converter. It uses the Diesel Exhaust Fluid (ammonia) injected earlier in the exhaust stream to convert the remaining NOx (Nitrous Oxide - NO, NO3, NO4, etc.) to N2 and water and O2 (Oxygen).

All this is explained fairly well in the Advanced Diesel with BluePerformance document that is floating around in this and other forums. I encourage you to seek it out and read it.

[JoosyJoos]

I bought a CPOed 2011 335d with 30k miles and within 10 days of owning the vehicle and only 600 miles of driving it, I had the same failure. It's been in the shop for 3 weeks because the part was back-ordered and needed to be produced in Germany. There was a nearly identical 335d in the shop next to mine at Hendricks North-lake BMW waiting on the same part last time I was in there. Hoping this is just a one time bad luck scenario and not something else... either way... pretty disappointing so far. The F30 328i loaner I received is pretty "meh" compared to the E90 IMHO.

[Yozh]

It beats me how an SCR will fail on a stock car, unless it is all plugged up with the urea. Would be great to get the one dealership removed from the OP's car and cut it out to see what is inside. The SCR canister is in two halfs with two different substrates that have fairly small openings. I suppose that a plugged up or poorly functioning urea nozzle may lead to some SCR plugging problems, but it is a far shot. What is crazy that they had to replace the whole thing from DPF to muffler tips, it's one solid part ;(

[Persian Whisperjet]

Also, the techs left this on the seat. Any idea what this is?

[Yozh]

Originally Posted by Persian Whisperjet

Also, the techs left this on the seat. Any idea what this is?

That is not a part of your car and is likely one of their diagnostic cables. You should return it back to them.

[dixy2k]

return it on ebay