Saturday, December 2, 2023


Will a DEF head problem ruin your trip?

By Russ and Tiña De Maris
For Robin and Ken, it was the trip of their dreams. Leave Florida in their motorhome, take four months, sightsee the Midwest, then on into Yellowstone National Park. Less than 100 miles into their dream trip they got a “check engine light.” Their motorhome’s DEF (diesel exhaust fluid) system tossed a code that could have “derated” their rig – meaning, don’t drive too far, and don’t drive faster than five miles per hour. They turned around and headed home. Their rig’s DEF head (sensor) put their plans on hold.

Problems keep getting bigger

In the last few days we’ve received e-mails from other motorhome owners with similar complaints. It’s bad enough for a DEF head to go on the blink, but it seems the problem gets MUCH bigger when you try to replace it. Chris has his own story: His rig’s DEF head has given up the ghost twice. “In the middle-of-nowhere Washington,” 250 miles from home, he too got “the dreaded check engine light.” Driving through triple-digit temperatures, he wasn’t sure what to do – but he knew he didn’t want to get stuck. He took his chances and managed to get safely home. The chassis’ builder dealer, International, told him the bad news: It’ll be a while before they can get a replacement DEF head.

How long is “a while”? Depends on who you ask. T.W. said his dealer first told him it could be three weeks before they can get another DEF head. Then they told him, at least another two weeks. Every week, says T.W., he gets an e-mail update from the dealer. Every week they tell him another date. Other owners say they’re being told it could be as late as August, even September, before the DEF head they need is delivered to the dealer. Then the clock starts for waiting for a technician to install the replacement.

More than an inconvenience

For Robin and Ken, it’s more than just an inconvenience. If you have already made reservations along with your plans, the cost of “cancellations” can ring up an additional financial burden. “We have cancelled an extensive range of reservations up through July 23,” they tell us. “If the part comes by next week we can take a more direct route to Minnesota and continue our trip as planned from there. If not, I’ll be making more calls to cancel reservations and we will lose more deposit money. We have lost about $150 so far and stand to lose as much as $1000 if we must cancel the entire trip, as some reservations at popular areas are non-refundable or require significant deposits.”

What is it with the long wait for DEF heads? We contacted Cummins, the engine manufacturer for the rigs we’ve heard the most about. They were quick to tell us that Cummins isn’t responsible for the DEF heads – the chassis manufacturers procure and install their own DEF heads.

Spartan speaks

Spartan, a manufacturer of a huge number of chassis we’ve heard about, has published its own explanation. “As a result of the global shortage of semi-conductors currently impacting all major vehicle manufacturers, Spartan RV is experiencing long lead times for some parts and accessories, including DEF sensors that play a role in controlling vehicle emissions.

“Due to this shortage, we have worked diligently with our supplier to secure a finite allotment of DEF sensors to meet the needs of customers who are experiencing failures. If your DEF sensor order was recently denied because your coach was not down/out-of-service during transit, our team will be reaching out to you to assist with getting service scheduled. We are committed to doing everything in our power to keep our customers on the road and are working diligently to return to normal inventory levels.”

Supply chain issues are top issues for many manufacturers today. But what’s the cause of these DEF head issues to begin with? Chris, who we mentioned earlier, said his first DEF head failure came with just 6,000 miles on the odometer. The next one failed at 14,000 miles. Just 2,000 miles later, he’s still waiting for the third replacement.

No voodoo, or violations of federal laws

We’ve asked Spartan to tell us the reasons behind the failures, and just what RVers can do to perhaps ward off the problems, short of employing voodoo or some method that will violate federal Clean Air Emissions laws. Some “enterprising,” or is it “questionable,” suggestions have been made on how to work around the problem. One frequently floated idea is to simply disconnect the rig’s speedometer and duck the “engine derating” problem. Not such a good idea. Some who’ve tried it report their transmissions have refused to shift, and in some cases, the engines have shut down altogether.

Others are suggesting another DEF head failure workaround. Investing in an advanced code-reader. Using the tool, they suggest that “clearing” the DEF system codes might allow an owner to continue on their way without the dreaded derating problem. We’re not sure how well it works – some worry the code will simply come back repeatedly. We’ll keep you informed.

In the meanwhile, we’d like to hear from anyone who’s suffered the dreaded DEF system problem. Has your DEF head died? Are you on a waiting list for a replacement? While the large number of folks we’ve heard from have been owners of motorhomes with secondary market chassis, we know of at least one instance where a Dodge Ram pickup truck owner likewise was cursed with the DEF head problem. We need to hear from anyone with a DEF head problem, regardless of what kind of rig. Please drop us a line,

We’ll keep the fire lit under the chassis manufacturers, and see if there any practical workarounds for this paralyzing problem.


Is it safe to run that cheaper Walmart DEF?
VIDEO: What You Need To Know About DEF


Russ and Tiña De Maris
Russ and Tiña De Maris
Russ and Tiña went from childhood tent camping to RVing in the 1980s when the ground got too hard. They've been tutored in the ways of RVing (and RV repair) by a series of rigs, from truck campers, to a fifth-wheel, and several travel trailers. In addition to writing scores of articles on RVing topics, they've also taught college classes for folks new to RVing. They authored the book, RV Boondocking Basics.



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John Casey (@guest_134767)
2 years ago

Two days ago Tiffin told me it might be 3 weeks. This morning got the sensor from Tiffin, overnight delivery. it is 22″ long, plus the pig tail…appears 21″ will be inside the tank. no idea what “GEN’ it is. “Sensor kit 325-0086-22-k” is on the package….Ebay has one that appears identical but with 13-k on the end. google search turns up little…Anyway, I have my weekend project set up now….LOL.

Keith B (@guest_134686)
2 years ago

Furthermore, you will get people claiming that “the DEF was too old, or too hot or the owner was too cheap to fill the tank or whatever” none of which are the cause of the vast majority of the failures. The cause is shared between the sensor manufacturer whose product is unreliable but then Cummins shares a lot of the blame for not having a plan for what to do in the case of a sensor failure. If the fuel tank level sending unit failed they don’t just blindly shut down the fuel pump and disable the engine ( after all if there’s no fuel then there’s nothing to pump, right?) do they? No. They engineer a fault tolerant system that allows for some common sense and judgement.

Keith B (@guest_134684)
2 years ago

The problem is that the sensors are having widespread failures. No one including the engine or sensor manufacturers know why they are failing. When they fail, sensors basically report to the Cummins ECM that the DEF tank is simultaneously: 1. Out of DEF fluid, 2. Full of water, diesel fuel or something else that’s not DEF 3. That the DEF fluid that is in the empty tank is not 32.5% Urea/67.5% water and 4. That whatever is in the tank or not in the tank, whatever, has no temperature at all!!The Cummins ECM should interpret those sensor readings as indicating CLEARLY that the sensors have failed since the readings are nonsensical. Instead Cummins interprets them as representing several independent, simultaneous, out of tolerance conditions and imposes a derate to “induce” (official EPA term) the operator to remedy the condition. Which, of course, can’t be done because there are no parts. Ironically, the emissions control continues to work normally. No increased emissions whatsoever.

John Casey (@guest_134582)
2 years ago

2020 37AP 5,000 miles, DEF Head sensor light is on. Ricky at Tiffin put us on the list. Part is back ordered….(you would think they would order 5000, based on what i have read)
Anyway, probably have to install it ourselves, no big deal. Got a trip planned. Hope all goes OK…You would think, Tiffin would make a work around for this. My code is DEF properties, 3521, what a dumb sensor….

Karen W (@guest_134294)
2 years ago

Mercedes Benz has a class action lawsuit regarding the emissions on Sprinter vans with Bluetec. Readers might want to call their local dealer to see if their vehicle qualifies for emissions work.

Wayne (@guest_133587)
2 years ago

Delete delete delete.
Our MPG are much improved by having deleted all the emissions stuff.
There is nothing that comes out of a tail pipe that didn’t come from the ground in the first place.

Neal Davis (@guest_133515)
2 years ago

Our recent week-long trip to the beach was short-circuited and included being towed twice and spending 10 days dry-camping in Freightliner parking lots. A part of the emissions system on our diesel pusher is a diesel exhaust filter (DPF). They are expected clog after 300k, or so miles of use. Ours got clogged at 39,000. They currently are a 44-day back order with Cummins. The first Freightliner dealer (Rocky Mount, NC) installed a 3rd-party filter to get us operational, but failed to search for a cause for the clogging. We limped to a second dealer (Greensboro, NC) where the problem was generally identified (exhast gas recirculation (EGR) manifold cover, EGR sensor, or EGR valve) and remedied (all were replaced). Along the way we were advised to buy DEF only at truckstops to avoid getting old DEF, which can cause severe engine problems. Yikes! I now understand why pre-DEF RVs are so highly valued and sought.

Last edited 2 years ago by Neal Davis
Tom Huyck (@guest_133511)
2 years ago

i’m relatively new. What is a DEF head ?

Drew (@guest_133525)
2 years ago
Reply to  Tom Huyck


It’s a cylindrical device with components inside that dispense diesel exhaust fluid to the exhaust emission side at the engine. It contains some sensing equipment that is the center of the problems being talked about everywhere.

Thomas B (@guest_133497)
2 years ago

I have had def troubles from the first 3000 miles
it’s been back to chev 8 times
ive found a mechanic that will delete def
next time it goes out I will pay him a visit
often it’s a poor quality def message but there is no drain on the tank to dump it and add fresh
bad engineering

Magee Willis (@guest_133784)
2 years ago
Reply to  Thomas B


Drew (@guest_133490)
2 years ago

I’ve heard that disconnecting the speedometer sensor has nothing to do with the trans or any other component…and there are plenty who have already done this ahead of any derate- saving them lots of grief. I don’t own a diesel but have done a lot of reading about this.

Bob M (@guest_133489)
2 years ago

Maybe the best thing to do is quit buying anything with a diesel engine that has Def Head problem. Our government is out of control with mandates.

Tony (@guest_133528)
2 years ago
Reply to  Bob M

Yea it is silly for our government to mandate against engines that poison the air that we breathe.

Magee Willis (@guest_133783)
2 years ago
Reply to  Bob M


Crowman (@guest_133479)
2 years ago

Most of these problems come from the owners of these vehicles that don’t understand the DEF fluid lifespan. DEF can deteriorate in hot weather sitting in your DEF tank causing the system to fail within months. On YouTube look up the “MotorCity Mechanic” channel he has 2 video’s on the lifespan of DEF that everyone should watch that owns one of these systems. I have gone over 53,000 miles with mine without a problem. He shows you that you can clean the head yourself to fix it.

Gary (@guest_133500)
2 years ago
Reply to  Crowman

Tried but couldn’t find it in his videos.

Craig (@guest_133846)
2 years ago
Reply to  Gary is the link to his videos. He’s a former Chrysler dealer mechanic who now runs his own shop. I happen to follow him on Facebook. Btw, I have a 2016 RAM Cummins Diesel with over 82,000 miles. When we first bought it, we had a high rate of DEF consumption which required a few software/firmware updates to the system before the issue was resolved. We have had no other issues with the DEF system however, I try to only buy fresher DEF. DEF goes bad in hotter temps and should be stored at cooler temps. Like I said, mine is in a pickup and it gets driven daily. I can see an issue in a motorhome where it sits unused for a long period time and heat will cause the DEF to deteriorate. There should be a way to easily drain and change it.

Ken (@guest_133473)
2 years ago

Been there. Done that. April 2019. I got all kinds of warnings, “low DEF” light, until I couldn’t add any more DEF fluid to the tank. Reno to Klamath Falls was cautious. Derated to a stop just 37 miles east of Medford, OR. Spent 2 nights in the yard. The codes and re-setting codes were baffling the young men on the third day. We were back on the road by 1 PM. Ours is a 2017 Fleetwood Discovery, 380 Cummins on a Freightliner chassis. Knock on wood!

Montgomery Bonner (@guest_133458)
2 years ago

Huge discussion on multiple threads of this issue on here. Spartan Chassis seem to be affected more so than freightliner, so if FL, not too much worries. Lots of reasons affecting solution, “chips” being only one part of issue. (10) Newmar Owners Club |

Don (@guest_133447)
2 years ago

The DEF Head issue is just the latest in a decade-long list of EPA Mandate debacles. They arbitrarily issued new, very stringent diesel emission controls requirements in 2007 that caused engine manufacturers to start improvising in an effort to meet them. In ’08 they came out with the infamous DPF/Regen systems which have caused (and continue to cause) major problems for owners. It was SO bad that Caterpiller, one of the most reliable engines on the market, simply pulled their over-the-road engines from the line-up because they’d failed to develop a reliable emissions system. Those of us who have those ’08-’11 Cat engines can attest to what a debacle this has caused. Then in ’11 the DEF system came into use, and as this article shows, that too is far from a perfect solution.
If I ever replace my ’08 Country Coach, you can be sure it will be with an ’07 or earlier model. Good luck with all those EPA mis-designed rigs!

Tony (@guest_133526)
2 years ago
Reply to  Don

EPA does not design. EPA sets emission standards that engine mfg need to meet so that the OTHER humans on the planet can breathe. If you have any doubts about the EPA regulations being necessary just visit cities in China where they have no regulations on diesel engines.

Dan (@guest_133439)
2 years ago

DEF is just another federal mandate purportedly saving the environment, and maybe it does help, but how do you measure it? The one sure thing is that manufacturers support these additions to our vehicles because they get to charge for them and charge us again when they need service. Diesels aren’t alone with these new features. I had to spend a bundle of money on our Class C to have the EVAP system repaired because it wasn’t venting properly and became extremely slow to fill with gas. There are shops out there that will eliminate these mandated features for you, but of course they are breaking the law. I have to admit that I replaced expensive catalytic converters with ‘test pipes’, but only my own stuff. DEF, EVAP, TPMS, examples of our government hard at work getting fat on political contributions.

Ed Day (@guest_133563)
2 years ago
Reply to  Dan

Truth That! Simple minds want simple fixes and someone else to tell them what to do. All the EPA mandated environmental regulations for modern engines; gas, diesel and alcohol, could be eliminated by simply producing high tolerance efficient engines.

Dr. Michael (@guest_133426)
2 years ago

Do you want horror stories?????

Go to IRV2 and look under the Entegra owners forum.
From the Forum, it sounds like it is not Spartan, but a company called Shaw Development that cannot seem to make a quality product. Add the EPA BS and you now have a perfect recipe for disaster.

Take one company with a very poor proprietary product
The EPA mandates
Chip shortage
Chassie manufacture who does not want to take any responsibility
No workaround to avoid being stranded for months
All the people who lost an entire summer of use because of this.

Stir in a lot of anger and resentment from owners of semi-truck, construction equipment, and motor homes- just about any diesel vehicle (Except emergency vehicles) that use a combination of a Spartan chassis and DEF equipment from Shaw.

Something really should be done. At the very least, Shaw, Spartan, Cummins, and Allison should get together and come up with a temporary solution to the problem so the owners of the vehicles are not stranded.

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