Broken DEF Header and possible workaround

[Jim]

There has been a lot of notice given to the DEF header recently, mostly because so many of us are experiencing DEF Header failures and having to replace them. I’m in that group, and during the days that it took me to sort through the workings of this beast, I’ve learned some things that could have saved me considerable money, both in repairs and in lost bookings.

I’m not an expert by any means, so what I’m passing on is what I’ll refer to as “on the job training”, and you need to do your own research before using anything that you read here. Also, the solution that I have chosen may/may not be the best one, but it is allowing me to continue with my trip until I have time to replace the DEF header correctly.

Before the failure, I had no idea what a DEF header was, what it did, or what it looked like. For all I knew, it could be the size of a piano, I had no idea. So for those who are in that same boat, the DEF header is about the size of a thermos, and here is what it does.

The DEF Header

A DEF Header performs several functions including,

• Measuring the level, or the amount of DEF that is left in the DEF tank,
• Monitoring the temperature of the DEF in the tank,
• Warming the DEF when the outside temperature gets into the freezing levels,
• Monitoring the quality of the DEF in the tank.

In the case of freezing temps, the monitor opens a valve that allows engine coolant to flow through the heating tube in the header, which warms the DEF and keeps it from freezing. The problem is with this valve, which has a tendency to fail, and when it fails, it generally fails in the “open” position. This allows the flow of heated engine coolant to flow through the heater tube in the DEF header, and results in overheated DEF, which produces a “Check Engine” light and in some cases, a derate situation.

The picture below is the top of my DEF header (2016 London Aire) and shows where the fluid goes into the header and where it comes out. To remedy the problem of overheating the DEF, I simple removed the hoses from the header and using a 5/8 brass connector, I connected them together which bypassed the header completely.

I’ll probably cover the entrance/exit connectors on the DEF header, but to be honest, I don’t know if it makes any difference whether I do or not. Also, 4 clamps (two on each side) are probably overkill, but I’m funny that way.

Again, I believe this (temp) solution will work for me, but it may not be the the right solution for everyone. I would rather replace the part and move on, but after 4 days of nonsense from the Ocala Freightliner shop up the road, it was this or an extended stay at the Holliday Inn Express.

I am open to questions and suggestions, so fire away!

To be sure and give credit where credit is due, @Rich W. was instrumental in helping me through this diagnosis.

 

[Neemer]

@Jim , if that resolves your immediate problem, I’m all about it. I believe I have read that DEF won’t freeze until you get down to somewhere around 11degF. Someone will correct me if I’m wrong I’m sure. *cough* @Rich W.

Personally, I would want to cap off those coolant fittings on the DEF header, but I don’t know that it’s necessary.

This is all to say I don’t know crap anything, but I’m glad you’ve found a way to remain viable.

 

[Buster]

Thanks for the pictures and description, good info and very helpful @Jim

I'm not sure I'll ever drive when temps are colder than 11F, so I may do the same unless there are downstream risks others may know about.

 

[jaydee325]

Failure of the temperature control valve in the coolant lines to/from the DEF header are well known. Temporary fix is to just clamp off the coolant lines until a proper fix can be done.

There are other failure modes as well and there is a def head simulator that can be built that can be plugged in in place of the DEF header and get you home or to a shop.

I don't like to link out to other RV websites but this post is but one of several that discusses the DEF header and problems as well as reference the simulator. Inmate Archer2 is a wealth of knowledge there. He mentions the simulator in post 4.

 

[Jim]

Failure of the temperature control valve in the coolant lines to/from the DEF header are well known. Temporary fix is to just clamp off the coolant lines until a proper fix can be done.

There are other failure modes as well and there is a def head simulator that can be built that can be plugged in in place of the DEF header and get you home or to a shop.

I don't like to link out to other RV websites but this post is but one of several that discusses the DEF header and problems as well as reference the simulator. Inmate Archer2 is a wealth of knowledge there. He mentions the simulator in post 4.

I wanted to go with the "simulator” but the fellow I spoke with said it only works on 2017 and above. Mine is a 2016.

 

[flyboy013]

Your temporary solution is a good one and will work as long as you aren’t driving where the ambient temperature is below 12°F. I’ve read of folks installing a ball valve so that they have the option of heating the DEF when needed. Obviously the right answer is to replace the OEM valve just in case you will be driving in freezing temperatures. Even better would be to replace the OEM valve and install the ball valve just in case the OEM valve were to fail again. Keep the ball valve closed except when you expect to be driving in freezing temps.

On my 2018 MADP (and I suspect your 2016 LADP) you can have Silverleaf display data on the console screen (the one where the rear camera is typically displayed). One of the parameters that can be displayed is the DEF temperature. Folks were surmising that the DEF temperature was getting too high due to the proximity to the exhaust. For a while I would monitor the DEF temperature to see if that was the case, but I personally didn’t see that happening. Here is a picture of my display with the DEF temperature and level shown. I took this picture with the engine off, so the values are not valid.

 

[Rich W.]

I wanted to go with the "simulator” but the fellow I spoke with said it only works on 2017 and above. Mine is a 2016.

Actually it‘s compatible with 2016 and later emissions systems, but some of us 2016 coach owners are lucky enough to have a 2015 chassis, so while the DSS wont work for us, we have less reasons to need it.

https://www.apta.com/wp-content/uploads/APTA_Presentation-Diesel-Aftertreatment-Systems.pdf

 

[Rich W.]

@Jim , if that resolves your immediate problem, I’m all about it. I believe I have read that DEF won’t freeze until you get down to somewhere around 11degF. Someone will correct me if I’m wrong I’m sure. *cough* @Rich W.

Personally, I would want to cap off those coolant fittings on the DEF header, but I don’t know that it’s necessary.

This is all to say I don’t know crap anything, but I’m glad you’ve found a way to remain viable.

unnecessary but it would prevent any possible contamination should you ever want to restore the system to OE specs. A couple slip on rubber 5/8“ caps would do it.

 

[Rich W.]

Thanks for the pictures and description, good info and very helpful @Jim

I'm not sure I'll ever drive when temps are colder than 11F, so I may do the same unless there are downstream risks others may know about.

It’s actually a good idea to do this proactively because you have no idea if or when the valve will fail, and when it does, as Jim has found, it fails in the “open” position, an EPA mandated condition to make sure that DEF can never freeze. Unfortunately what they failed to consider is that heat is also the enemy of DEF and renders it ineffective causing DTCs and possible derate.

So while failing in the open position will prevent DEF freezing (at under 12°F) it will also cook your DEF in higher temps, rendering your SCR ineffective and stranding you. What fun. It may also lead unsuspecting and innocent victims of all this insane oversight to spend upwards of $4k correcting a situation that, as Jim found, can be addressed for around five bucks. Think about that for a moment.

There are no other down stream risks - the system will never know the difference unless you are driving in sub 12°F temps. If you anticipate such conditions, the appropriate solution is to install a manual valve on the input side rather than a by-pass. That way you can activate or delete the heater as you feel necessary.

 

[Rich W.]

“Obviously the right answer is to replace the OEM valve just in case you will be driving in freezing temperatures”

You can’t just replace the OEM valve because its part of the DEF header. So as @Jim found, this replacement comes at a considerable cost: $1200 or so for a new header, and whatever the shop you happen to land at thinks is “fair” - in Jim’s case a couple more thousand bucks! Insane in my estimation if not criminal!!!! (note that I borrowed several of @Kevin D Pem ‘s exclamation points).

You can replace the entire DEF header and hope that the valve in new unit doesn't fail, or you can just by-pass the valve. Since it is totally unnecessary for 99.768% of RVers, it only makes sense to by-pass it and forget it.