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#1 2021-02-01 17:20:46

Registered: 2016-03-18
Posts: 368

DPF Regeneration process

Elsewhere I have written about my DPF woes, and the one thing that I discovered was how much general misunderstanding there is, on how the system is supposed to work in practice. I argued with the master tech at the dealership to get some figures as to what is normal - but they refused to tell me.

So here is what I now know based on logging my (nearly) new system, hopefully it may help someone.

The ECU calculates the volume of soot in the DPF - there is no sensor.
Once a pre-determined limit is hit, in my case at 5g/l after 550 miles, the active regeneration process is initiated. At this point the "distance since last regeneration" counter freezes.
Assuming that there is enough load on the engine to drive the exhaust temperature high enough, the soot will be burnt off in about 10 minutes, the process will stop, and the "distance since last regeneration" counter resets to zero.
However if the temperature does not stay high enough then the process can stop early. For example I got caught in slow moving traffic, and the process stopped at 3.5g/l. So in this case the next regen happened again at 5g/l, but after 125 miles this time.

The ECU maintains an average of the last 10 regeneration cycles, however it does not really tell you much, if, as in the example above, the regeneration often stops before it has finished clearing the soot, the average will be lower.

One last point, the differential pressure measurement across the DPF is a backstop. In my case this was the primary mechanism for activating the regeneration, at calculated soot levels sometimes below 1g/l after 50 miles.
Clearly this was wrong, however the master tech failed to pick up on it.


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