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Billdozer2 · 01-13-2017, **(Subject: Fault code 3751 )**

So, I'm doing a forced regen for giggles and ha ha's after I changed my engine oil today. Numbers are looking good. DPF pressure is 0.5. About an hour passes and it stops. I'm thinking everything is A-O-K. So, I check active faults just to see if anything was logged. No check engine lights. Just a hunch. I find code 3751 is active. Using Quickserve, I find that 3751 is a code used only to help diag other fault codes. Using the diag tree, it basically says check the ECM software and delete the code. Anyone ever seen this fault before? Apparently, it does nothing to the "performance" of the engine. No other codes active nor inactive were logged.

BTW, 3751 is Aftertreatment SCR Catalyst System-Mechanical System Not Responding or Out of Adjustment

I think my truck is trying to tell me something. Like, Help! I want to breathe properly!

Rawze · 01-14-2017, **(Subject: Fault code 3751 )**

On a CM871 engine, it should take 40 minutes exactly for a forced regen to finish if it is even somewhat healthy.

Not sure about a 2250, but an hour seems excessive like something is wrong.

Billdozer2 · 01-14-2017, **(Subject: Fault code 3751 )**

(01-14-2017 )Rawze Wrote: Not sure about a 2250, but an hour seems excessive like something is wrong.

I think the 2250's take at least an hour. Every time I've done a forced regen on my truck using Insite, its taken between 60 and 90 minutes.

I've never known why it takes that long, but it seems to go through ok.

Anyone else done a forced regen on a 2250? How long did it take?

01-14-2017, **(Subject: Fault code 3751 )**

can take up to a hour. that code basically means your SCR is not working. it measures nox inlet and outlet and its seeing its not reducing nox enough. that is a very serious code which will come with serious derates after about 50 engine hours if it not solved.

It can be nox sensors, bad scr, exhaust leaks, bad urea injector, bad urea, bad urea pump, etc, etc. that is not a nuisance code its your truck telling you its scr isnt working.

gemarsim · 03-14-2018, **(Subject: Fault code 3751 )**

It s not being much activity on this topic recently but I'm having similar issue right now. Same codes with No Check engine light on. Code 3751 spn 4792 is active and force regen does not come to an end by itself after 90+ minutes in two consequential tries.
Recently I am getting 3383 inactive EGR system date a valid but above normal operating range moderately severe level.
I have never tried to do something with the DPF or catalytic converter never open the tubes.
Never had an issue with clogged filter after almost 200,000 miles which I put on the truck for couples years now is close to 600k miles.
Am I wrong if I think I have to replace the catalytic converter which is close to three thousand dollars and bake the filter?
Any other suggestions will be greatly appreciated.

Rawze · 03-15-2018, **(Subject: Fault code 3751 )**

Since it has not been apart in a long time, I would start by replacing the sensors, pull off the DOC and DPF, take pictures of their faces and post them here,.. then send em off to have baked out and flow tested. Use your cellphone to take pictures inside the decomp tube to ensure it is not partially blocked and snap a picture of the face of the SCR element too.