Sprinter DPF regen going backwards

Odd occurrence. 2nd time we’ve noticing this happen. 🤷🏼‍♂️

Last week we drove from SLC to SF and found on our 750 mile trip that the regen on our 2020 MB Sprinter 3.0 V6 only happened once. 🚐💨

Here’s the odd part, it actually went up to 80% and then started going backwards slowly for an hour down to about 61%. Stalled there for another hour and then taking a slow hour and a half to hit 100% before regen. 🔥

Now after that regen, it went quickly to 20% then slowly (like normal) to 70% and now back down to 60% only to seem to act normally climbing a little bit on the last 20 miles. Photo is just after it dipped down this most recent time to 60%.

⁉️Wait… WTF is regen and what is the DPF!? ⁉️

Diesel engines are highly efficient and powerful, but their emissions contain high levels of pollutants such as particulate matter (PM) and nitrogen oxides (NOx), which are harmful to both human health and the environment. To address this, modern diesel engines are equipped with diesel particulate filters (DPFs)and diesel oxidation catalysts (DOCs).

DPF Regen is:💨

the process by which the soot within a DPF is converted to ash through the use of heat, chemical reactions, and/or electricity. Soot combustion temperatures range from the 250˚C – 350˚C range (with a chemical or fuel catalyst) to the 550˚C range (without a catalyst).

After regen when you step out of the van you might here a super hot exhaust under your Sprinter cracking and pinging as it cools down from this super heating cycle.

Here’s why we’re writing this post:

Now in the MB manual it’s states that 3 interrupted regens (stopping the van and turning off ignition) will cause a CEL (check engine light). And we can confirm that. We had this exact thing happen to to us idling for long periods at times.📛

And more alarming, 4 incomplete regens can cause the van to go into "limp mode". It also can also cause problems such as engine failure that MB won't cover. 😳

Digging into this further we discovered there are two things happening with the regen - "active" vs "passive" regen.

When you're driving and the EGT gets hot enough, it'll start a passive regen and you'll see the value drop (slowly) - this might happen if you're driving on the highway, in the mountains, etc. If you're poodling around town, then the EGT won't get hot enough, numbers will increase, and then once you hit 100%, an active regen will start and burn everything off until you hit 0%.

Despite what others say, keeping an eye on this is the correct thing to do, especially if you take a lot of short trips, drive around town, etc. - if you interrupt an active regen more than three times, the van will start complaining and you might very well run into trouble.