The dpf system consist of a doc-dpf-catalyst.
doc catches the soot from the engine and a regen burns that soot to ash and is caught and stored in the dpf,the catalyst just takes care of nox.
at the outlet of the doc is a tube with rubber on it and nother tube goes to the outlet of the dpf, the sensor the tubes hook to is called a differential pressure sensor and when pressure between the 2 cans reaches a threshold it trigger a parked regen,now 2 things could be wrong either the differential sensor is bad or the dpf is plugged with ash, I have also found that the clamp that holds the pressure sensor gets loose and let the sensor slide down the dpf and when that happens water that forms from condensation cannot drain off and plugs the port giving a false reading,the tubes should be angles up to the sensors at about 10deg you should be able to look at that and rule it out for free,any question I would love to help .
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