The way I have discerned negative pressure is based off of my Foxwell scanner. At idle, I am observing around -8 to -1 mbar, and while driving I can see values ranging from -20 to -80 mbar. When pressure testing the DPF, we confirmed that pressure from the DPF appears to be fine. Would having a cracked EGR cooler throw any codes? If codes aren't being thrown, is there any other way I could verify the issue? Thanks again for your time and assistance!
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Originally Posted by wcs531
So after googling the new codes you had these dont necessarily say "negative pressure", which is what I was going off of before.
4CF3 Exhaust back pressure signal, sensor, dynamically implausible
4D01 Exhaust backpressure sensor, signal too low, diesel particulate filter differential pressure too low
4D99 Particulate filter system, minimum differential pressure under shot after regeneration, particle filter flow resistance low Bank 1
From the NA BMW Diesel facebook group when searching 4D99:
The 4D99 DPF code is due to pressure drop being TOO LOW across DPF after regeneration, suggesting the DPF either has a large hole thru its filter matrix (unlikely, but possible), or there's an issue with an exhaust leak which is MUCH more common (ie DPF is not plugged up).
Definitely sounds like an exhaust leak if youre smelling exhaust all the time. My guess would be the EGR cooler (different from lower EGR) which cracks fairly often. Hopefully not a cracked exhaust manifold. There should be a number of exhaust leak threads to dig through
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