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2025 Cummins Regen Observations

It's very strange to me. Bank 1 Sensor 1 is much cooler than the rest. Bank 1 Sensor 2 gets the hottest, having gotten as high as 997° today. I'm still only at 88% on the DPF trigger. I have a 200 mile trip coming up, so hopefully it'll go into a full regen and all of this will go away. It's absolutely killing my mileage right now while it's doing whatever it's doing.

Update: I typed this post right after parking at the shop. Had to hop back on the road maybe 30min later, and it's no longer doing it. Also note that this whole time it appeared to be doing some kind of regen, the DPF meter kept climbing instead of decreasing. I'm at 90% as of now. MPG is back to normal as well as temps.

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PyroJoe said:
It's very strange to me. Bank 1 Sensor 1 is much cooler than the rest. Bank 1 Sensor 2 gets the hottest, having gotten as high as 997° today. I'm still only at 88% on the DPF trigger. I have a 200 mile trip coming up, so hopefully it'll go into a full regen and all of this will go away. It's absolutely killing my mileage right now while it's doing whatever it's doing.

Update: I typed this post right after parking at the shop. Had to hop back on the road maybe 30min later, and it's no longer doing it. Also note that this whole time it appeared to be doing some kind of regen, the DPF meter kept climbing instead of decreasing. I'm at 90% as of now. MPG is back to normal as well as temps.

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It is in line with what I see. There are two DOCs. One before SCR and second one before DPF.
 
Finally got to the next regen. It didn't start till about 2 miles after hitting 100% on the trigger. Bank 1 Sensor 6 is the gauge to watch for your max regen temp. I got right up to 1100° at one point. Another interesting observation was the trigger went from 100% to 64% instantly when it started.

Question - Is it safe/worthwhile to park the truck in Neutral and let it finish the regen? Mine only quits regen in Park. Not sure if you can do elevated idle in Neutral, but I doubt it. I've been planning to do a max mpg test tomorrow for the past 2 weeks. It's just my luck I'm in the middle of a regen cycle now. Gonna have to just "drive around" tomorrow till it finishes.

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I don't think you were in regen before, nothing indicated it. Something else was causing high EGT's, try looking at engine load.

Regen will shutoff if you are stopped too long or put the truck in P (I think N too).
 
AH64ID said:
I don't think you were in regen before, nothing indicated it. Something else was causing high EGT's, try looking at engine load.

Regen will shutoff if you are stopped too long or put the truck in P (I think N too).
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How in the world would I have high engine load when parked and also while coasting down the highway? It was doing something weird with the DPF for sure. You don't just hit 1100° idling or coasting otherwise.
 
PyroJoe said:
How in the world would I have high engine load when parked and also while coasting down the highway? It was doing something weird with the DPF for sure. You don't just hit 1100° idling or coasting otherwise.
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I agree the EGT alone would indicate regen (active or passive); however, the truck wasn't reporting anything else indicating you were in an active regen and you weren't towing so it wasn't passive. All the other data suggests you we're not in regen.

That's why I wonder if something was dragging the engine down, or there was something else going on.
 
I'm happy to report that I'm coming up on 5,000 miles and I've only had 24-hour scheduled regens. I'm probably a good stress test... between RV trips, this is my daily driver. Unfortunately, I've been forced to idle longer waiting for my kid at school pickup and such. It's not ideal but the truck is handling it perfectly. Only on one cycle did I see the EVIC get to 30%. I'm currently at 18 hours since last regen (~350 miles) and I'm at 10%.

We're going on a trip with the camper in a week and I'm hoping to time the regen to happen while towing with 6400D in the tank!
 
AH64ID said:
I agree the EGT alone would indicate regen (active or passive); however, the truck wasn't reporting anything else indicating you were in an active regen and you weren't towing so it wasn't passive. All the other data suggests you we're not in regen.

That's why I wonder if something was dragging the engine down, or there was something else going on.
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With this new aftertreatment arrangement on the '25's I wonder if they are doing some small in cylinder dosing to get the exhaust temp up in the SCR for more efficient operation?
 
PyroJoe said:
How in the world would I have high engine load when parked and also while coasting down the highway? It was doing something weird with the DPF for sure. You don't just hit 1100° idling or coasting otherwise.
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Agreed. I'm not always watching it but I've never noticed a high temp like that outside of an active regen. I'm just using my phone with OBDLink to monitor so it's not always open.
 
superjoe83 said:
With this new aftertreatment arrangement on the '25's I wonder if they are doing some small in cylinder dosing to get the exhaust temp up in the SCR for more efficient operation?
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That would completely defeat the purpose of a seventh injector. The SCR only needs around 350°F
 
I don't remember where I saw it, but I found some Stellantis literature the other night that said after a truck as idled or driven at a low enough RPM for a certain amount of time (I think it said 1 hour), the idle would raise to 900 RPM and you'd notice a lack of WOT power. Maybe this is what I experienced. But again, my DPF gauge didn't drop after this cycle completed, nor did my trigger %.
 
Were you idling for an hour? Rpms go to 900?

That used to be called, and might still be, net zero idling. It’s not technically a regen but rather an idle mode to reduce emissions and soot buildup at idle only, such as in park. It shouldn’t happen in gear.
 
AH64ID said:
Were you idling for an hour? Rpms go to 900?

That used to be called, and might still be, net zero idling. It’s not technically a regen but rather an idle mode to reduce emissions and soot buildup at idle only, such as in park. It shouldn’t happen in gear.
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I didn't specifically look at RPM, but I know it stopped doing whatever it was in Park as I previously mentioned. But it would do it in gear and in neutral, stopped or moving, foot on the brake or not.
 
PyroJoe said:
I didn't specifically look at RPM, but I know it stopped doing whatever it was in Park as I previously mentioned. But it would do it in gear and in neutral, stopped or moving, foot on the brake or not.
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How long had you been stationary when it started?
 
I don't really want to say as my memory is a big foggy, but I believe I had to drive about 5 miles before it'd start showing this behavior. It's been over a week now with lots of miles logged since then, so I'm not positive.
 
PyroJoe said:
I don't really want to say as my memory is a big foggy, but I believe I had to drive about 5 miles before it'd start showing this behavior. It's been over a week now with lots of miles logged since then, so I'm not positive.
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Unless it took you a couple hours to go those 5 miles that does not sound like the net zero behavior, but if it was a very slow drive, there could be new strategy for net zero idling with the seventh injector. But that doesn’t explain why it went away in P
 
They didn't elaborate on whether it had to be 1 hour of idling all at once without stopping or 1 hour accumulated over a period of time and starts/stops. I certainly hit that hour of idle within a week's time, but never all at once before moving again.
 
For net zero the idling has to be at one sitting.
 
AH64ID said:
That would completely defeat the purpose of a seventh injector. The SCR only needs around 350°F
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Please keep in mind that 7-th injector is just before DPF's DOC. First DOC - mounted right after turbo outlet does not have it's own injector. It was shown - even in this thread that this first DOC is activated sometimes and there is no other way to heat it up different than in cylinder dosing.
 
AndyRoos said:
Please keep in mind that 7-th injector is just before DPF's DOC. First DOC - mounted right after turbo outlet does not have it's own injector. It was shown - even in this thread that this first DOC is activated sometimes and there is no other way to heat it up different than in cylinder dosing.
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SCR has not ever needed or used in-cylinder dosing, why would they start now? Exhaust temps from driving are sufficient to let the SCR reduce NOx with DEF.

Adding in-cylinder dosing for the SCR, when it’s closer to the engine, would be the opposite of what they are trying to accomplish with the 7th injector. That’s the point.
 
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