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Originally Posted by FaRKle!
Yes, "regen" is when extra fuel is being burned in order to bring your diesel particulate filter (DPF) temps up to 1000-1300F (typical temps are 400-800F) in order to burn off the soot in the DPF into ash. I use an OBDII bluetooth device and the Torque Pro app on my android phone to see my DPF exhaust gas temps (EGT) so I know when the car is undergoing a regen. Shifting out of drive during a regen might cause the regen to abort.
You say it only started occurring in 20k miles, but perhaps you've just been "lucky" and not had a regen occur during idle prior to that? If you shut the car off during a regen sometimes the fan will come on and run for a while to cool things down.
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Very helpful information FaRKle! Yes, the fan does come on now from time-to-time when I shut down the engine and always wondered what that fan was trying to do. Anyway, TY! and I hope to run some of these ideas by my service center next time I’m in. I’m surprised they never mentioned the nuances of the regen process and effects on the engine. And yes, you’ve described my experience perfectly--so, a handful of times I’ve parked the car and when i got out I could hear a fan running and thinking ‘wonder what that’s about' so, this sounds like I may have turned off the engine during a regen? I’ve had the car some five plus years now and can probably count on one hand the number of times this has happened. Can’t recall it ever happening in the first couple of years but it happens sometimes now. Also, would you know if BMW’s N47 engine bases the regen on mileage (perform a regen periodically whether it’s needed or not) or does it actually measure the pressure differential on either side of the DPF to determine when the DPF is clogged and needs cleaning? Does it inject diesel directly into the DPF to clean it (bypass the engine) or does it add the diesel as part of the exhaust stroke from the engine?