Regen issue followup

2637 DOC face plugged.
4214 DOC temp increase below desired during a regen

The temp increase is not happening across the DOC. You have to watch a regen with Insite to see what is going on. Usually it is dirty or malfunctioning aftertreatment injector. Other more serious issues if the system is not getting hot enough to allow the injector to fire in the first place. Basically the engine itself creates about 550 degrees of exhaust heat by closing the turbo and increasing RPM. If during a regen the temps never get hotter than about 480 something is wrong with the engine. A good cheap place to start is removing your intake pressure sensor and seeing if it is plugged. Clean it out. Then replace your exhaust back pressure sensor and retry. The aftertreatment injector will not spray until the exhaust is at least 550 or so. Once the injector starts to spray the DOC will covert that 550 into 1100 or so. The fault is being set because this temp increase to 1100 is not happening at all. If the engine can make 550 then you are looking at cleaning or replacing the aftertreatment injector. (I recommend to just replace it). There is more you can do, but only if you have access to Insite and able to perform a forced regen and watch data.

 

The DOC is made just like the catalytic converter in a car. The DOC has a cell structure made with a precious metal coating that reacts with the fuel that is injected during a regen. The heat of the exhaust from the engine, plus the fuel makes a catalytic reaction to create the extreme heat needed for a proper regen. What happens is, over time this precious metal coating simply wears away and degrades to the point where it is no longer effective. So unfortunately, there does come a time when it needs to be replaced. This is no test for this or visual indication to confirm the health of the metal coating that I know of. Replacement is just kinda a last resort type of thing. We always remove and clean BOTH the DPF and DOC when servicing is needed. The DOC can also get just plain dirty and need a good cleaning. If you have never had the DOC simply cleaned, I would recommend that before spending the big bucks on a new one. The DOC should be cleaned in a proper machine just like the DPF.

 

You can graph temps within the after-treatment system to get an idea if the DOC is bad, this is not always accurate though. Lately, we've seen a few DOC's failing on units with roughly 300K on the clock. A unit that has had a long history of coolant usage usually fails a DOC sooner.