I'll keep it simple as I can (don't know much more)
You are discussing TWO seperate systems on our trucks.
The OP's original question was about the Diesel Particulate Filter or DPF.
Then, the Diesel Exhaust Fluid - DEF - came into the thread.
Both are smog items required by the government. MANY of us cannot "Delete" either of these and get license plates in our states. Also, deleting the DPF would be very costly in the great reduction your truck would have for trade-in/sale value. The DPF is very, very expensive to replace so a truck without one would be worth far less in states that require them, and that list of states continues to grow. (thanks EPA)
OK, the DPF collects the solid particles that are part of diesel exhaust. You have seen them as black smoke. A stock 6.7 Powerstroke does not blow any black smoke if it is working correctly. The DPF looks like a large muffler with sensor wires coming out the sides (look under your truck). I believe they are made of a honeycomb ceramic stuff.
As the diesel works the DPF collects carbon particles until it "fills up". Sensors tell the computer the DPF needs cleaned and thats when you get the info in your read-out on the dash "cleaning exhaust filter". Extra diesel fuel is introduced into the exhaust flow and burns. This causes the DPF to become very hot (like a self cleaning oven) and burns the collected particles into harmless ash which is blown overboard.
This cleaning cycle lasts up to 20 minutes which include heating up, burning clean and then cooling back down to normal temp. If possible, try to run your truck long enough for the cycle to finish - - but you do not have to do this.
If you shut down before the cleaning cycle finishes, it will begin all over again the next time your truck is at operating temp. If you shut down during a cleaning cycle you will prolly smell the "heat" of the exhaust system as it has not got to the cool down portion of the cycle. Do not touch any part of the exhaust as it will be extremely hot!!
Now, on to the DEF, , , , ,
DEF is injected into the exhaust as the truck runs. The amount injected varies with load, temp and other factors but it is injected most of the time the engine is running. DEF reduces the vapor emissions in the exhaust.
There you have it - - DEF is for vapor control and the DPF collects solids. TWO seperate systems but both are in the exaust plumbing.
I have to say these systems both work well. I can run my truck in the garage and never smell diesel oder. If you watch your mirror while you are at full throttle, you will not see any smoke (unless you are lucky enough to be able to delete these systems).
As far as the cost of the DPF - I'm not sure but I have heard 10 grand!! I do know they are not cheap and you do not want to throw a good one away. I have also heard Ford expects the DPF on our trucks to last at least 100k miles so it is not something that will ding our pockets often. Just don't toss it away in the garbage if you take it off!!!