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retnasaguy · 01-27-2021, 12:34 PM

I know this subject has been discussed but, I can't find an answer to the problem.
Problem: when DEF goes into regen mode, shortly after that, truck goes into limp mode and remains there until power is removed at the battery. This only happens when towing a travel trailer, solo it's fine.
I have been to Ford and have been told I must replace the entire system($$$$), various other less expensive fixes, to just drive it solo until regen is complete. Needless to say, none of these are practical solutions. Any Super Duty diesel wizards out there??
Truck is a 2016, 6.7l, F-350, CC, long bed with automatic transmission. TIA
Cheers

jimcumminsw · 01-27-2021, 05:33 PM

Will first off DEF has nothing to do with regeneration.

Second DEF is used in the SCR emission system.

"Selective Catalytic Reduction (SCR) is an advanced active emissions control technology system that injects a liquid-reductant agent through a special catalyst into the exhaust stream of a diesel engine." IE: DEF

What goes into the regen cycle is the DPF.

Now what CELs or ECM codes are being displayed that could be stored in the ECM. This will point you to the proper component to fix.

TMyers17 · 01-27-2021, 05:55 PM

To clarify, when your truck goes into regeneration, shortly after, your truck goes into limp mode until you pull the battery cables resetting the system. Is this correct?

My first thought is your truck's computer is getting a signal from the Diesel Particulate Filter (DPF) that it is full. There are pressure sensors at both ends of the DPF. The computer measures the difference in the exhaust pressures between both sensors. When the pressure shows restriction at around 50% in the DPF, it triggers a regeneration.

The process of regeneration is pretty simple. When triggered, the computer sends diesel fuel through an injector directly into the already hot DPF. This causes the DPF to super-heat up to approximately 1200 degrees. The built up DEF and soot gets cooked into white ash.

Lots of short trips and idling for long periods is hard on our diesels.

Either your DPF is nearly full or you have a faulty pressure sensor making the computer think it's full. This would cause the limp mode.

Diesel Exhaust Fluid (DEF) can cause a limp mode but only by running out of it. If you run out of DEF, your truck will start a mileage count down. Ram's is 150 miles, not sure if Ford is the same but would guess so because it's an EPA thing, not a brand thing.

I would get someone to do a Forced Regeneration on your truck. This is done where the truck is stationary. The dealer can do it but most shops with a higher end scan/diagnostic tool can do it as well. DON'T park beside the truck or do it over grass. It will get hot!

Gary RVRoamer · 01-28-2021, 11:09 AM

It may be academic, but regeneration is part of the DPF system. DEF is associated with the SCR (catalytic reduction) system. Both are part of diesel emissions management.

retnasaguy · 03-04-2021, 08:44 AM

Update:
Turns out it was a faulty EGT sensor that was sending false readings to the computer causing a regen condition. New sensor, no more problem.
Cheers