Thursday, January 27, 2022


Stranded motorhomes. Is Cummins to blame?

By Russ and Tiña De Maris
Earlier this month we wrote about the plight of flocks of RVers, sidelined or scared-to-death by their Cummins-equipped motorhomes. Imagine yourself far from your home base when your dash warning light alerts that there’s a problem with your diesel exhaust fluid (DEF) system. You have 100 miles to go to get help, or your engine will progressively “derate.” That means, you’ll reach a point where your maximum speed could be as low as five miles per hour. You know your engine maker: Is Cummins to blame?

How DEF works

A little history is in order. Diesel engines have a nasty habit of producing unhealthy byproducts in their exhaust stream. These emissions include nitrogen oxides and particle emissions which are linked to lung and heart problems, some of them chronic. In 2010 the Environmental Protection Agency (EPA) mandated reductions of both these exhaust products in medium- and heavy-duty vehicles, which included plenty of diesel-fired motorhomes.

The smog treatment system of choice utilizes DEF, which is a fluid that’s largely water with added urea. The beauty of a DEF pollution control system is that engine manufacturers can build a big, powerful engine and not have it stifled by air pollution control equipment, as the DEF system is an “after treatment” system. After your engine has roared out plenty of horsepower, the nitrogen oxides and particulates are blasted down the exhaust pipe, and sprayed with DEF. When DEF comes into contact with the nitrogen oxides, it converts them into harmless water and nitrogen. Seems like everyone should be happy: Motorhome drivers have engine power, and there’s less harmful pollution released in the atmosphere.

“DEF head” issues

In the last few months, however, scores of motorhomes, delivery trucks, and other DEF-using engines have been having issues. The pollution control devices that monitor the condition, use, and presence of DEF in systems, often equipped with Cummins engines, have been acting up. Monitoring systems are reporting a variety of “faults” with the DEF equipment. When that happens, the dreaded sequence of events begins. Get that DEF system fixed, or find yourself “de-rated,” maybe stuck in a repair facility. Is Cummins to blame?

Our initial contact with Cummins representatives regarding what many call “DEF heads,” or the DEF monitoring assembly, yielded this response: “This is not a Cummins part and my understanding is that it is procured by the chassis manufacturer, so you should probably ask them about this particular part.” True enough, chassis manufacturers like Spartan and Freightliner have their own sources of DEF monitoring assemblies, so to a degree Cummins is not to blame. We attempted contacting Spartan for comment, but the company never bothered to respond.

But there’s more here than just a monitoring assembly. A Nexus Ghost owner, who asked to not have his name used, approached us. He and his family were headed out on vacation in their motorhome, and a few hundred miles from home got the dreaded DEF sensor failure light on their dashboard. They ended up parked in an International dealer’s parking lot. “Sorry, but we don’t have that part available, and we’re not sure when we can get it.” The family had to make their own way home, and the motorhome languished on International’s back lot.

The real cause of the problem

Not satisfied to sit on his hands, this RVer posted his experience on an internet forum. In a flash, other Nexus owners responded that they, too, had been sidelined with DEF sensor problems. Not all were stranded – some had made it safely to their home base. But all had one thing in common: None of them could get the needed repair parts, and most got only vague answers as to when they might get them.

What’s the problem? It seems that many chassis builders were concerned that since DEF is largely water, when ambient temperatures go down, the danger of the DEF freezing rises. If the DEF freezes it may degrade, and potentially we could imagine expansion of liquid in a reservoir might cause physical damage. To avoid that issue, these DEF systems are fitted with a valve that allows hot water to be pumped through the system to keep the DEF from freezing. Sad to say, these valves are prone to failure. In the “fail” mode they are stuck open, allowing hot water through the system regardless of ambient temperature. How does that lead to a DEF sensor failure?

The heart of the DEF sensor system is a silicon microchip. Microchips are particularly sensitive to high temperatures. That’s why when you fire up your computer, you’ll hear a fan or two running – cooling those persnickety microchips. In the height of an engineering “Duh!” you’ll likely find your DEF sensor chips nestled right next to one of those hot water lines. Too much heat, and the chips give up the ghost. For our Nexus Ghost owner, chip failure meant a quick stop, waiting for a replacement.

The chips are down

Is Cummins to blame? Not directly, but in the end they might be the folks with the ability to make a fix. Point the finger at COVID-19, but you’ve heard the cry of complaint from auto manufacturers to appliance makers: We can’t get the chips! This is the same problem for the scores of unhappy motorhome owners. There is a genuine shortage of microchips, and the end of the shortage is not in sight. If you can’t get the chip, then your chips are down.

Cummins doesn’t build the sensors. Cummins doesn’t install the sensors. How is Cummins to blame? Or how can they help? We go back in history. When the EPA trotted out its rule that led to the manufacture of oceans of DEF, someone recognized a fly in the ointment. Imagine you’re on the golf course and have a heart attack. Somebody calls 9-1-1, and the paramedics jump in their diesel-fired ambulance to come pick you up. Oh, dear! That dreaded DEF system failure light comes on and your ambulance engine is de-rated. Would you get to the hospital in time at five miles per hour? Or if your house were burning, how long would it take fire engines to arrive at the same speed?

Cummins’ “solution” for emergency vehicles

Cummins was concerned that emergency responders could not be hampered by a DEF issue, or other emissions control issues. The EPA issued a “Direct Final Rule” that provided relief to emergency vehicles. Essentially, the rule said emergency vehicles could not be slowed down, nor have their torque reduced, simply because of one of these issues. Cummins’ response, in their own words, was that they “developed a new engine software specific to fire and emergency vehicle calibrations … This new calibration eliminates all emissions related vehicle speed or engine power (torque) derates. This includes derates associated with low level Diesel Exhaust Fluid (DEF), incorrect and SCR faults that some customers may experience ….”

Cummins isn’t building fire trucks and ambulances leaving out essential pollution control equipment. They’re simply programming their monitoring systems so that in the event that something goes buggy with the sensor (or even if someone failed to fill up the DEF reservoir), the engine will continue operating at full speed. Warning lights still indicate the system has a problem.

Your motorhome isn’t a fire truck. If it’s sidelined with a DEF sensor issue, is Cummins to blame? No. But Cummins, who is the holder of the proprietary rights to the DEF monitoring control software programming, might be able to help. Our Nexus motorhome owner, who works in the tech industry, thought perhaps they could. Why not have Cummins do a “software patch” that would do the same thing for motorhomes that it does for emergency vehicles?

What industry and government say

Our source approached both Cummins and the EPA. He tells us that high-level officials in the EPA admit they are aware there is a serious problem for RV users who are being sidelined by DEF sensor fault issues. He also told our source that as far as he could see, the EPA would be happy to consider issuing a temporary waiver that would allow industry to issue such a software fix – long enough for the microchip industry to catch up and allow a more permanent and less-polluting solution. But, he said, Cummins would have to petition the EPA to start the ball rolling.

Our Nexus friend reached out to Cummins, eventually reaching Tony Satterthwaite, Cummins’ Vice Chairman. He explained his own problem about his sidelined motorhome. He brought up the suggestion of Cummins asking the EPA for the waiver. Something that could possibly get these stranded RVers back home, or out of their yards. To his credit, Satterthwaite assigned a Cummins engineer to the case. The engineer’s “workaround” investigated using a different DEF sensor. Not the specified sensor, but one that might “make do.” Sad to say, the one that was located was a bit too tall to fit his motorhome. But a sharp-eyed mechanic at the dealership recalled they had a DEF tank and sensor. It had been taken out of another piece of equipment. Lo and behold, it was the exact DEF head he needed. He now has his motorhome back home after weeks of waiting.

Cummins’ answer to RVers

But what about the suggested waiver request? After a great deal of back-and-forth, Cummins’ Satterthwaite wrote back: “During our communications, you suggested that Cummins should seek a temporary waiver from the EPA to allow for the deactivation of engine de-rate protection for the DEF quality level sensor, given the supply constraints affecting the industry. We appreciate your suggestion, and we will continue working to ensure that our customers have timely access to parts like the DEF quality level sensor.” In corporate-speak, “NO.” Is Cummins to blame if your motorhome is sidelined? We’ll let you draw your own conclusions.

Let’s be clear: The EPA won’t necessarily grant the waiver that could put sidelined motorhomes back on the road. They might – they might not. But to its credit, the agency is evidently at least open to the suggestion. The ball is decidedly in Cummins’ court.

You can share your thoughts with Cummins management

Would you like to share your thoughts with Cummins management? Cummins’ Director of External Communications is a gentleman named Jon Mills. He’s assured us that if you direct your messages to him, he will “ensure that the leaders are made aware as appropriate.” You can e-mail him directly at

That this problem isn’t something that will go away soon is witnessed to by the plaintive email we received this past Friday afternoon. It’s from one of our readers, Bill N. He writes, “We had the dreaded three codes signifying the DEF head failed while starting the RV one morning. We have 18,000 miles on our 2018 Entegra Anthem, and are stuck 850 miles from home.” It’s too far for Bill to walk home. Maybe Cummins could buy him a bus ticket.

This article did not write itself. It took valuable time. And it is only possible because of the support of our voluntary subscribers. Every contribution, no matter how much, makes a difference. Are we worth more than “Free?” Do you appreciate in-depth articles like this that make a difference to you and other RVers? Then please consider a voluntary subscription now. You choose the amount, big or small. Do it here. Thank you.


Is it safe to run that cheaper Walmart DEF?

Revision notes: 07/28/21 2130 PDT, revises Cummins’ contact information, per their request. 



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Roger Becht
5 months ago

This article was titled wrong. There should be no mention of Cummins being to blame. Put the blame where it belongs, with the EPA. Look back at the evolution of diesel pollution controls, there is a great video on youtube. After the initial attempt they just stuck on more bandaids instead of going back to the beginning and and redesigning the entire system.
The chassis manufacturers should be where a large part of the responsibility is placed.

John Boy
5 months ago

Hi all @ RVTravel.
After reading the article and most of the post I thought I look at the JAYCO owners forum and I found 2 threads regarding this issue. We own a 2017 Jayco Seneca pre S2rv Chassis. Our 2017 has the M2 Chassis. From reading ALL the comments in the 2 threads it seems the issue is occurring on the Freightliner S2rv chassis and the cause is the DEF coolant lines were installed backwards. On majority of all the issues posted that was the main caused which entailed replacing the DEF Header and another sensor. Also all of the people having the issues are not involving Cummins, they are working with Freightliner.
Here are the 2 links if you’re interested. I don’t believe you need to be registered on the Forum to read, only to post comments

From Jayco’s site


crane man
5 months ago

I work for a crane hire rental company and all of our crane engines that use DEF are Cummins QSB 6.7 liter engines. This is the industrial version of the Ram truck engine. We have the same failure problem. Loss of the DEF head sensor signal to the ecm results instant derate for these engines. Imagine a crane opertator holding a 30,000 lb load and suddenly with no warning loses all throttle response. These engines come from Cummins Central Power in Indiana. And the head is made by Shaw Development. We have discovered that when DEF codes pop up, we remove the entire tank assembly. Remove the sensor & head assembly. Drain the tank. Rinse the tank and the sensor completely with distilled water. Place the sensor in a clean bucket and fill with distilled water and soak for about an hour. Reassemble with fresh new def fluid. This has worked on at least two of our machines this month. So far the machines are on rent and no faults yet.

crane man
5 months ago
Reply to  Russ De Maris

Please check your email.

5 months ago

I’ve heard of the issue but this article gives understanding. Glad my CAT is pre dev.

Mark S
6 months ago

Cummins does not supply the urea QLS sensor. It’s not their responsibility. There is only a few different companies that make the sensors. They are all very tempermental. The problem is if you program the engine ecm to not derate anymore, when will they be put back to factory configuration? Because the reason for this is to save the afterteatment system from self destruction and to make sure it will get fixed. These systems are very expensive to replace bad components. If any part has to be replaced it is several thousand dollars.

Keith B
5 months ago
Reply to  Mark S

How exactly would disabling the derate cause damage to the SCR system? Also note that even in an emergency vehicle with the firmware that eliminates the derate installed, they still will have all kinds of lights and alarms if there’s no DEF in the tank. And even with derating disabled every single component of the emissions control systems continue to operate exactly as they are designed to. Do you understand that the failure is in the system that only monitors and reports the amount and condition of the DEF fluid in the tank, not the systems that pump the fluid, inject the fluid into the exhaust, monitor NOx emissions, filter particulates, etc.?

Dr. Michael
6 months ago

This article was written very well in plain language. But I see you left out the biggest obstacle in the room- Shaw Development. Shaw and their sorry excuse for engineer’s design and manufacture of a very poor product.
What makes this interesting is that they (Shaw) know they have a problem on their hands and I think they also know that the law suits will be coming. What did they do? Sold out to a private equity firm (Monomoy Capital Partners ( to relieve the burden of their poor quality. The contact at Monomoy is Justin Hillenbrand. Perhaps he can assist in increasing the quality and expedite the shipping of the DEF products to the owners/dealers.

Roger V
6 months ago

Best summary yet of why I will Never own a Diesel engine on any vehicle. My gasser may not set any land speed records going up mountains, but it gets us where we want to go every single time!

Last edited 6 months ago by Roger V
Terry Burnett
6 months ago

Easiest way to avoid def issues is to delete it out of the ecm and block off all the bs. And run it like a pre egr motor

Jeffrey Millikan
6 months ago

I believe that GM trucks have
had recalls also related to blue def issues

6 months ago

Isn’t emissions equipment warranted for 100,000 miles.

Terry Burnett
6 months ago
Reply to  Gary

It dosen’t matter about warranty if the manufacturer can’t get the parts to the distributor and they cant get them into the hands of the techs that are waiting for the parts to get the vehicle back in tbe road. I run into this on a weekly basis working on over the road trucks and trailers.

6 months ago

I can tell you that getting a waiver from the Epa is going to cost money. Is Cummins expected to foot the bill? The mechanic won’t install that software for free. Nor should they. Then, months later once the supply chain is sorted out, who is going to ensure those engines are returned to factory configuration? Is Cummins supposed to cheerfully pony up for everything? Remember, they didn’t create the problem. Yes they can do a lot to relieve it, but don’t think for a minute that this would be cheap and easy for them. The best way to make this happen is communicating to Cummins that you ( the RV owner) would chip in. And don’t forget, the epa will be expecting proof that those vehicles get returned to factory spec. Even the ones living in areas without emissions testing. They are likely to hang that responsibility on the manufacturer, since the Epa knows where to find them.

Keith B
6 months ago
Reply to  Russ

Who said anything about free? What does Cummins charge for any other software patch to fix a problem. I bet its a lot cheaper than renting a hotel room in West Undershirt, Texas for a month or two while you wait. Again, in case you didn’t read the comments before you jumped in, this software has been around since 2014. it’s in every Cummins-powered firetruck, ambulance, forest fire fighting vehicle (including the tractors to pull the flatbeds that carry the dozers to the forest fire). It’s not exactly like Cummins would have to re-engineer the space shuttle.
As far as your assumption that owners would never have the sensors replaced remember that even with the “no derate” patch, the vehicle is still going to have a veritable New Years Eve party of flashing lights and squawking alarms every time the engine is started. I’m pretty sure the owners will be sprinting to the dealers to get the fix done when parts are available.
i don’t think you really understand either the problem or the potential fixes.

Donald N Wright
6 months ago

Wherever I went on vacation, I heard the same story. “You cannot tow that trailer with an F-150 gasoline engine, you need a one ton truck with a diesel engine”. Heh, heh, no problem.

6 months ago

Rather than blame Cummins, or any other manufacturer, why not bring chip manufacturing back to the United States where we can control the quantity and quality.
Then the DEF head issue can be resolved quickly and cheaply.

5 months ago
Reply to  Barry

The bringing back manufacturing part would be great, but we made our bed so now we sleep in it.

John Klein
6 months ago

Once in awhile I think a new truck would be nice…but I think I will keep my 2006 3500 Cummns with the 5.9L and no DEF issues or concerns.

Magee Willis
5 months ago
Reply to  John Klein

Likewise. Like my dually and it is probably going to last as long as I do. Has been extremely reliable for 200,000+ miles.

Bob M
6 months ago

Glad you provided the Cummins management contacts. Hope those with DEF issues contact then and let them know how they feel. Would be good to provide management contact information to others that have issues with their RV’s. We need to stick together to improve quality and safety with RV’s and their parts/equipment.

Miller B
6 months ago

Another reason for DEF sensor failures is the coolant lines running to the DEF heater were connected at the factory in reverse. This causes the DEF tank to be heated ALL the time, this is what happened to mine. There is even a service bulletin bout it…”SS 1034491 False DEF Fault Codes”

R Pollock
4 months ago
Reply to  Miller B

Just curious, if the coolant lines keep the def from freezing , what happens when you shut the engine off for the night in cold climates.

Tom Janzen
6 months ago

That was a really well-written article. I understood it completely the first time through even though I’ve had no experience with a diesel engine, ever.

6 months ago

How many coaches are sidelined due to DEF sensor failure? How many DEF equipped vehicles are there in the US. Asking Cummins to fix another manufacturer’s defective hardware is a real stretch. Cummins would be responsible for 100% of the Governmental red tape, monitoring, modifying, certifying, installation, tracking of replacement sensor; then reprogramming units after the problem vanishes. How many owners of modified coaches would actually allow the mod to be removed???…….a real pipe dream that comes from arm chair engineers….turned writers IMO

Keith B
6 months ago
Reply to  Engineer

First, nobody has (yet) said that the proximate cause, the failed sensors, is Cummins fault. Nor has anyone suggested that Cummins has a legal requirement to ask for waivers. What IS being suggested is that Cummins and the EPA are the only parties involved who can deliver some equitable relief to their innocent customers. You aren’t seriously suggesting that Cummins never does anything that it’s not required to do legally? I would suggest that they spend millions of $$ on customer and investor relations. Have you ever seen the presence they have at the Indianapolis Motor Speedway during the Indy 500?
The firmware used in emergency vehicles for years that eliminates the most draconian “inducements” is already written. The implementation is no more complex than having the tech who gets assigned to repair the disabled vehicle use the Cummins INSITE tool (PC) to install the EV Calibration instead of changing the currently unavailable sensor until a permanent fix is available.

Keith B
6 months ago
Reply to  Keith B

Also, nobody has said that it should be free and it should be noted that nothing being suggested would affect the performance of the SCR emissions control system at all. Let me repeat that. The emissions controls remain the same and actual emissions from the tailpipe are not affected.
I don’t know what kind of engineer you are but the ones I know, including myself, don’t usually respond to a problem by saying “don’t even try to solve the problem, it’s too hard”

Ron Lane
6 months ago

I’ve read somewhere that the sensor (head) was added to the DEF units in 2017 and that prior DEF units did not have this sensor and therefore is not subject to this problem. It indicated that pre-2017 units could not distinguish the UREA/water solution from just plain water and that owners/users were bypassing the system by just using water. Once the new sensor was installed on all engines manufactured in 2017 and later, the sensor problem came into being. Any truth to this?

John D Jorgenson
6 months ago
Reply to  Ron Lane

As a diesel technician my self. I can say that is not the case. The reason for the change is more grounded in the money department. The older system would use the two nox sensors, one before and one after the scr to decide efficiency. If it was low the tech would be directed to check Def quality and dosing amount first and then test the scr etc. By adding a sensor for Def quality they can now diffentiate between scr efficiency and Def quality so they pay lower warranty repair bills. Sadly enough for the bean counters the Def quality sensor is crap so there warranty cost has actually skyrocketed. I work for a peterbilt dealer and the rule as of today is we can order 1 sensor per dealer per day. So 20 trucks come in we can order 1 sensor. So 20 days to get the last truck back on the road. I get the rv thing but think about the trucks owned by people who use them to make a living and it takes 20 days to get a sensor. I personally am surprised we don’t have more violent melt downs from people when explaining this. The epa is killing small trucking companies. Just my opinion.

Terry Burnett
6 months ago
  • And i bet you understand completely when someone brings a deleted truck in 
Chris Mead
6 months ago

Russ, well written article. We’re all in this together. I will write Cummins today with a respectful email. I suggest all reading this and operating a Cummins motor do the same.