# Car seemed stuck in perpetual regen



## MRO1791 (Sep 2, 2016)

What monitor are you using to see the regen? I have seen Torque freeze, and that could be the issue. It may be the monitor that is telling you it's in regen that is stuck. An actual regen that long is very odd, but it can take longer if you are changing speed, and it falls out of regen if you do a long downhill run. Decel kills the temps to keep the regen going.


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## spaycace (Feb 9, 2012)

When I experience something similar to this, I tend to downshift to a lower gear to raise RPMs for a minute or two ... sure it kills my mpg, but then again, so does the regen process. I watched my trip mpg drop from nearly 51 mpg to 36.9 during a regen cycle!


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## Barry Allen (Apr 18, 2018)

MRO1791 said:


> What monitor are you using to see the regen? I have seen Torque freeze, and that could be the issue. It may be the monitor that is telling you it's in regen that is stuck. An actual regen that long is very odd, but it can take longer if you are changing speed, and it falls out of regen if you do a long downhill run. Decel kills the temps to keep the regen going.


I was watching the fuel economy bar on the display and it was perpetually stuck around 30 mpg while driving about 55 mph on very flat roads.

Going downhill isn't a problem if it's a gradual downhill. On those occasions you'd see the fuel economy spike to 99 mpg (infinity, basically) because no fuel is being used. While in regen on a slight downhill grade, I'll see it read something like 70 mpg when I know it should be 99. When it does that I know it's not using any fuel on the power stroke but the ECU is still injecting extra fuel during the exhaust stroke to burn soot out of the DPF.

This regen cycle was just taking way too long. Something was obviously stuck. After a single restart, it's like it rebooted the ECU and didn't do it again that I can tell right now.


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## MRO1791 (Sep 2, 2016)

Barry Allen said:


> I was watching the fuel economy bar on the display and it was perpetually stuck around 30 mpg while driving about 55 mph on very flat roads.
> 
> Going downhill isn't a problem if it's a gradual downhill. On those occasions you'd see the fuel economy spike to 99 mpg (infinity, basically) because no fuel is being used. While in regen on a slight downhill grade, I'll see it read something like 70 mpg when I know it should be 99. When it does that I know it's not using any fuel on the power stroke but the ECU is still injecting extra fuel during the exhaust stroke to burn soot out of the DPF.
> 
> This regen cycle was just taking way too long. Something was obviously stuck. After a single restart, it's like it rebooted the ECU and didn't do it again that I can tell right now.


OK, so you can't be sure it was a regen by MPG alone. I get it that it was strange behavior, but if you actually have a monitor to see when it's in regen, you would see that it goes in and out of active regen based upon many factors, like high engine power demand (can interupt regen) or low, power, like decel, and downhill (absolutely interupts regen). The ECU will try to keep EGTs up, thus MPG will be suffereing, but if it is not in the temperature band for regen, the regen is not active. Sounds like in your case the regen was interupted many times, and that will prolong the over-all progress of the regen. Without a monitor to know, the MPG is interesting, but it's not conclusive proof. I have seen MPG vary when it's not in a regen and for no obvious reason, not as dramatically as you describe, but sometimes it gets really high MPG, others lower, and same roads, speeds and conditions. There are many variables that affect MPG.


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## Barry Allen (Apr 18, 2018)

MRO1791 said:


> OK, so you can't be sure it was a regen by MPG alone.


I entirely disagree with this. There is zero reason my car would be at 30 mpg whole doing 55 mph in 6th gear on flat roads. There wasn't any weather factors (driving into high winds) because I drove both north and south on the same road.

The only time the car has ever been this low fuel economy is either when it is in a regen cycle (engine is fully up to temperature), or when it's right after a cold start and there is excess fuel being burned to warm up the exhaust emissions systems.


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## MRO1791 (Sep 2, 2016)

Barry Allen said:


> I entirely disagree with this. There is zero reason my car would be at 30 mpg whole doing 55 mph in 6th gear on flat roads. There wasn't any weather factors (driving into high winds) because I drove both north and south on the same road.
> 
> The only time the car has ever been this low fuel economy is either when it is in a regen cycle (engine is fully up to temperature), or when it's right after a cold start and there is excess fuel being burned to warm up the exhaust emissions systems.


Disagree all you want, the fact remains that Regen is active only when a set of parameters are met, the big one being temperature. Actually having 3 of these cars (Gen 2s, and also one Gen 1), and the ability to actually monitor them with a real time display of active regen, I can say from observation that it will not stay in active regen when the conditions are not met, but it will still be trying to ramp up EGTs to get back and complete the regen. That process lowers MPG. For instance, the throttle valve is partially closed to cause actual vacuum in the intake in an effort to bring up EGTs. I've seen it. I recommend if you really want to understand what is happening you invest the about $200 (or less) to get set up with BiScan for GM and Torque, or the Gretio app from Snipesy. Then you will see it's far more complicated that just paying attention to MPG.


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## Barry Allen (Apr 18, 2018)

MRO1791 said:


> Disagree all you want, the fact remains that Regen is active only when a set of parameters are met, the big one being temperature. Actually having 3 of these cars (Gen 2s, and also one Gen 1), and the ability to actually monitor them with a real time display of active regen, I can say from observation that it will not stay in active regen when the conditions are not met, but it will still be trying to ramp up EGTs to get back and complete the regen. That process lowers MPG. For instance, the throttle valve is partially closed to cause actual vacuum in the intake in an effort to bring up EGTs. I've seen it. I recommend if you really want to understand what is happening you invest the about $200 (or less) to get set up with BiScan for GM and Torque, or the Gretio app from Snipesy. Then you will see it's far more complicated that just paying attention to MPG.


I think we are talking semantics.

What I experienced was an unreasonable extended period of time where the fuel economy of the car was hovering around 30 mpg because it was either in regen, or heating the exhaust to try to regen. This is unexplained for my car because it was at least 4-5x longer than any other regen cycle. There was no reason that a car fully up to temperature (and not in extreme cold weather) for an hour would be stuck in regen or heating for over 30 minutes.

I won't spend $200. I'll just shut the car off and restart like I did, because that fixed the problem. It was just very weird.


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## MRO1791 (Sep 2, 2016)

Barry Allen said:


> I think we are talking semantics.
> 
> What I experienced was an unreasonable extended period of time where the fuel economy of the car was hovering around 30 mpg because it was either in regen, or heating the exhaust to try to regen. This is unexplained for my car because it was at least 4-5x longer than any other regen cycle. There was no reason that a car fully up to temperature (and not in extreme cold weather) for an hour would be stuck in regen or heating for over 30 minutes.
> 
> I won't spend $200. I'll just shut the car off and restart like I did, because that fixed the problem. It was just very weird.


You'll spend quite a bit more than the $200 on the monitor the first time it needs a Service Regen at the dealership, something you can do yourself at home with that set-up. But, you are free to do as you wish obviously. The mystery of what your car was doing will remain a mystery as you won't have the data to get an idea of what the issue mihgt have been, just know that is the decision you have made. 

My manual Cruze did something strange also, and I'm still under 30K miles. It had a short interval of only 90 miles between regens.. then the next regen is appearing to be a bit longer than normal (for this car).. but without a clear way to see what is going on, the MPG method would only cause confusion. 

I've also been able to observe that for whatever reason, the Manual vehicle does almost twice as many regens as the autos, and in similar driving patterns. My theory is that the lower final drive ratio of the auto transmission leads to higher sustained EGTs at highway speeds, which I can observe becuase of that ability to monitor, this in turn does more passive regen of the DPF.. but it's an educated guess.


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## Barry Allen (Apr 18, 2018)

MRO1791 said:


> My theory is that the lower final drive ratio of the auto transmission leads to higher sustained EGTs at highway speeds, which I can observe becuase of that ability to monitor, this in turn does more passive regen of the DPF.. but it's an educated guess.


I think the MT cars do just fine at highway speeds. I drove cross-country to Seattle and back, and I observed a single regen cycle somewhere in the middle of Montana, immediately after a refueling stop.

I've observed that my car routinely does that. I'll be driving at highway speeds with everything at hot temperatures, stop to refuel, and then when I pull back to highway speeds the car immediately does what appears to be a shortened regen cycle. I believe the ECU programming looks for certain conditions like that: everything up to temperature, a stop where the fuel tank is filled up, and then if you are up to sufficient speed it immediately kicks into regen to clear the DPF even if it's only a short regen cycle.

From my observations, it seems that highway speeds keeps the DPF below a certain soot load. I can say that my trip across Montana was with the cruise control set at approximately 95-100 mph, so that's high enough speed to keep the DPF lit and burning up just fine.


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## MRO1791 (Sep 2, 2016)

Barry Allen said:


> I think the MT cars do just fine at highway speeds. I drove cross-country to Seattle and back, and I observed a single regen cycle somewhere in the middle of Montana, immediately after a refueling stop.
> 
> I've observed that my car routinely does that. I'll be driving at highway speeds with everything at hot temperatures, stop to refuel, and then when I pull back to highway speeds the car immediately does what appears to be a shortened regen cycle. I believe the ECU programming looks for certain conditions like that: everything up to temperature, a stop where the fuel tank is filled up, and then if you are up to sufficient speed it immediately kicks into regen to clear the DPF even if it's only a short regen cycle.
> 
> From my observations, it seems that highway speeds keeps the DPF below a certain soot load. I can say that my trip across Montana was with the cruise control set at approximately 95-100 mph, so that's high enough speed to keep the DPF lit and burning up just fine.


My observation remains. The 2 Gen 2 autos I have average far fewer regens than does my Manual. This is very similar driving patterns. I've had the manual go into a regen with mostly highway miles at 90 miles from prior regen. The lowest on either of the autos was like about 300 miles, with mixed driving, mostly they go 600 miles between regens, the manual about 300 miles. I also monitor the EGTs, since I can see tons of data with my set up. The EGTs on the autos at highway speed is HIGHER, and that is almost certanly due to the lower final drive ratio. This can also be seen in boost pressure, the manual will be clost to zero, the autos run a constant 3-5 psi boost at level highway speed.. that is a difference.. and the regen behaviour is almost certainly due to that. 

Now I don't drive 100 mph, but that would certainly boost EGTs!


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## Carminooch (Mar 23, 2018)

Not sure if this helps but above 65mph and if I’m driving at steady speed, my soot levels _generally_ don’t increase much unless I drive hard briefly. I’m surprised with how well the car seems to passively regen as I drive on the highway. It’s only when I drive around town that I notice my soot levels increase. I can confirm by the Bluetooth obd2 adapter I use.


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