RVers face enough trip interruptions already. Now there’s one less for some. The EPA is making changes that will affect anyone who drives a diesel-powered pickup, motorhome, or tow vehicle. New guidance for diesel exhaust fluid (DEF) systems aims to stop trucks from suddenly losing power when DEF runs low—a problem that has frustrated RVers, farmers, and truckers for years.
Many modern diesel engines use DEF in the selective catalytic reduction (SCR) system to nearly eliminate harmful nitrogen oxide (NOx) emissions. Without enough DEF, most trucks automatically cut power, dropping into “limp mode” and sometimes leaving drivers stuck far from help. For RVers, that can mean being stranded miles from the nearest service station or campground.
EPA DEF rule changes for diesel rigs
EPA Administrator Lee Zeldin announced the changes at the Iowa State Fair, saying the agency heard from small businesses and everyday drivers who’ve lost valuable time and money when their diesel-powered equipment failed due to DEF system rules. “It is unacceptable that farmers, truckers, construction workers, and many other small businesses continually experience failures of diesel-powered equipment when they need it most,” Zeldin said.
Under the new guidance, truck makers will be urged to update DEF software not only on new models (starting in 2027) but also on existing vehicles. The updates will allow much longer run times before a truck’s power is restricted.
For example, heavy-duty pickups—including RV tow rigs—will now be able to run 80 hours or 4,200 miles on low DEF before being limited to 45 mph. Semi trucks get even more leeway: up to 10 hours or 650 miles before a 15% power drop, and a full 160 hours or 8,400 miles before the 25-mph cap kicks in.
Matters for RVers
This matters for RVers because many modern motorhomes also run on DEF. That includes most Class A diesel pushers built after 2010, Super C rigs based on medium-duty truck chassis, and Sprinter-based Class C models. If you have a Cummins, Caterpillar, Ford, Ram, Freightliner, or Mercedes diesel from the last decade-plus, chances are you have a DEF tank.
The changes mean RVers will have more time to get to a store, truck stop, or service center if they run low on DEF. For “roads less traveled” RVers, it’ll be a blessing when traveling in rural areas where DEF can be hard to find. Instead of a sudden slowdown or speed cap ruining a day’s drive, the updated rules build in a much bigger cushion.
GM’s Duramax diesels already give multiple warnings before DEF runs out, starting at 500 miles remaining. But if you do hit empty, it still takes adding about two gallons (half a tank) to get back to normal. Now, with the EPA pushing for software updates, more diesel rigs will offer the same kind of “get there before it’s too late” window.
For RVers who count on their diesel to pull a heavy fifth wheel, push a big motorhome, or handle mountain passes without drama, these changes could mean the difference between finishing the trip as planned and spending an unexpected night on the side of the road.
DEF tips for RVers
- Check before you roll: Always know your DEF level before starting a long travel day.
- Carry extra: A sealed 2.5-gallon jug of DEF is cheap insurance, especially in remote areas.
- Mind the shelf life: DEF typically lasts about a year if stored cool and out of sunlight. Heat can shorten that time.
- Use the right fluid: Look for DEF that meets ISO 22241 standards—it’ll be labeled on the jug.
- Keep it clean: Use a funnel if your DEF fill port is awkward to reach, and don’t let dirt or fuel get in the tank.
With the EPA’s rule change and a little DEF prep, RVers can head out knowing they have more time—and miles—before a low DEF level becomes a trip-stopper.
Sources include gmauthority.com
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RVT1222b
Sure would have been nice to have these upgrades when I had the truck. I had major problems with it and this new fix was around $700.
i traded for a new gasser. Less power but more reliable
don’t miss the repair bills
Didn’t know that it took that long for common sense to kick in.
Sounds to me like one more deep-sixing of environmental regs that were designed to put the brakes on climate change. Why is this any more an issue than expecting diesel drivers to stay on top of their fuel consumption? Why is it unreasonable to expect diesel drivers to stash a 2.5 gallon can of DEF “just in case”? And what the hell is reasonable about allowing 80 hours of running time in which the oblivious or devil-may-care can continue spewing nitrogen oxide? This is the sort of ruling that will only harden attitudes toward RVers by those who already see them as a pampered, self-centered bunch giving lip service to the glories of the great outdoors.
I’ll dip in for a 4th scoop of Russian caviar and contemplate the changes to the climate on Venus. So nice sitting here in my monogrammed Balenciaga lawn chair, sipping on my glass of 40 year old scotch. Mmmmm, sooooo good. Now where did I put that darn cigar cutter? I think I left in the pocket of my silk smoking jacket…. there it is. Cheers, to the good life. 🥂🍾
Happy trails ✌️ 😎
Make it an aged Kentucky bourbon and my LazyBoy and I’ll join you.Cheers back to you!
Ah, yes. Fiddling away while Rome burns. . . .
Not a single objective scientific study using accepted scientific methodology has ever found a correlation between mankind’s activities and climate. Climate change has however been an amazing tool to make people change behaviors and a great narrative for scientists to get funding. Fear moves money pieces around the board. Hopefully, with the dissolution of DOEd, we will no longer indoctrinate children into the church and cult of climate change and we can let this myth go the way if the dinosaurs…. which BTW, lived on a planet over 9 degrees C, warmer than ours.
Amen.
Sounds to me that you were fiddling away while you poured more fuel on the fire.
Some people never learn when to stop fiddling.
Andy,
Go check your science books from the 60s. Climate change is always with us. We came out of a mini ice-age in the late 1800s. Climate ALWAYS changes and not just because humans are on the planet. In fact, scientists are saying that we are coming out of the global warming phase (unless you believe those “scientists” who are power hungry). Think about why Greenland is called “Greenland” when it was covered in ice as we were growing up. When the Vikings settled there, it wasn’t covered in ice.
Climate Industrial Complex.
a) Would “extreme and extremely rapid” climate change make a difference to you?
b) “Greenland” was a deft marketing ploy to get people to move to a large ice-covered mass that was millennia in the making.
c) You’re right about one thing: those power-crazed scientists are rubbing their hands in glee over their success in taking over the world.
Thank you for the voice of reason and critical thinking (the other national deficit)
Perhaps you can explain to all of us trogs, how the climate on Venus is changing at the identical rate as earth? Most of us Trogs think it has something to do with the sun but perhaps it is mankind?
If you choose to look at some real science, you will find that our atmospheric CO2 levels are at historically and almost catastrophicly low levels compared to periods when our planet was in its healthiest state.
Happy trails ✌️ 😎
Actually Greenland was covered in ice during the Viking days. Eric the Red called it Groenland (Greenland) to give it a favorable name in order to get others from Scandanavia to settle there.
And in fact, Erik the Red lived about 300 years before the Little Ice Age which spanned from mid 14th century thru the 19th century. It got real icy 300 years after his death for about 500 years. I’m glad we are coming out of that ice age even still, and thus warming up a little. 3 cheers for some natural planetary warming.
Happy trails ✌️ 😎
Nice try, Jim, but you won’t make any headway with folks who make up whatever facts suit their narrative, tossing in non sequiturs like Venus and a “little ice age” to account for thousands (not hundreds) of years of sheet ice accumulation. They’ll still be babbling about “objective scientific findings” that they don’t begin to comprehend, but which they believe will give their views some authority if they just express themselves forcefully enough. No fool like an old fool with just enough education to be dangerously wrong. . . .
I think you might be in over your head a little here Andy. You are saying that:
1. A 500 year long Ice Age in the last millennium is a non sequitur in the study of climate science?
2. A lack of an objective scientific study on climate change causation is a non sequitur in climate science?
3. The Sun’s impact on planetary climate in our solar system, is a non sequitur on climate? You know, that burning ball of gas in the sky with a core temperature of 27,000,000 degrees F.
That’s kind of like saying hydrogen has nothing to do with water and that oxygen has nothing to do with fire.
Happy trails Andy ✌️ 😎
I would agree about carrying DEF fluid. But I had problems with 2 sensors at 2 different times that gave me the warning that I had 200 miles before going into DEF mode. Read my reply above.
“If you have a … Caterpillar … from the last decade-plus, chances are you have a DEF tank.”
Cat stopped producing on-highway engines in 2010. It lost around a half billion $ on its gamble of which tech would win for cleaner engines and pulled out of that market, so NO ONE has a Cat DEF engine.
The issue hasn’t been people “forgetting” to keep DEF in the tank. The major issue was sensor failures from the 2015 EPA rules requiring monitoring of DEF urea concentration and temperature. Certain sensor manufacturers had high failure rates with low availability during the pandemic for replacement sensors.
If the new rule doesn’t address that, it isn’t much help.
Thank you for the news, Russ and Tina! One interesting aspect of Canada (at least BC and Yukon, if not more broadly) and Alaska is the absence of truck stops and, along with that, the absence of DEF dispensers at the fuel islands. Instead, DEF is only available in the 2.5-gallon jugs. Thus, far less convenient to add DEF to ones RV north of the lower-48. Have a great day and safe travels!
I always carry extra DEF. Walmart has it and sometimes Costco does too. Nevertheless, I do worry about the tank sensor failing. That limp mode delay equates to improved safety. I do have a question: when the sensor fails is DEF still being dispensed to the exhaust system?
Yes. If the sensor fails the system is still functioning. The failed sensor is not reporting to the ECM the correct data, so the ECM “thinks” there is an issue, but there isn’t.
A few years ago a group of RVing techie guys developed a sensor “simulator” so that if a sensor fails (you can tell by the codes it throws) you can unplug it and plug in the simulator. The simulator sends a set of data to the ECM that kills the derate so you can safely get your rig to a repair facility.
I must have missed the important part of WHERE & WHEN can we get the update!
Snoopy
I’ll be asking my mechanic. I’ll let you know what he says.
Nobody is towing anything with a Cat engine “from the last decade” unless their tow rig is a piece of heavy equipment.
And no, low DEF Limp Mode isn’t some random thing to protect penguins.
It’s there to prevent damage.
The DEF pump isn’t designed to run on air no more than your engine can run long without oil. The SCR isn’t designed to operate without occasional DEF injection anymore than your toilet seal likes to see some water on it.
Love it or hate it, the engine is designed and tuned to include the usage of DEF. Running it without DEF isn’t good. Running it longer is worse as it only adds to the degradation of your engine.
The problem is not running out of DEF but the failure of the sensors in the DEF system that can get you limited to 5 MPH in the middle of nowhere even with a full DEF tank. The old rule was stupid and can get you in a very dangerous situation, for you and those driving near you. The new guidance makes sense.
But Bosco, de-rating doesn’t occur instantaneously my friend. Yes, if you drive 80 miles with a fault code, deration will start but it isn’t without warning. Repeated warnings….
Short sighted and shameful. DEF exists for good reason. There is no “back road” traveler who should ever run afoul of DEF shortage. No different than keeping fuel filled and planning your stops, as we all must. And there is absolutely no farmer or worker who would have any other problem with DEF besides negligence…it’d much more likely the desire to just save money. And this “convenience” and saving comes at the expense of the environment we all are out there RVing to enjoy. Crazy that RVers, of all people, should be backing these unnecessary rule changes. And yes, I drive a diesel rig.
I agree with most of your comment. I also like that my deisel exhaust is no longer black smoke. I, like many, was inconvenienced with a bad head sensor but no issues since replacing in 2021. I do carry an extra jug of DEF. I’m all for improving air quality but then, who isn’t?
I’m not sure shameful is correct however, sometimes life just happens. Maybe the new regs swing too far but perhaps the old regs were a bit too punitive.
The old regs were too punitive. The new regs will be their own punishment if individuals try to run these systems with no DEF for that long a time.
As I said in my above post, the thought that people have to wait extensive periods of time to find and fill their DEF tank is ludicrous. During the pandemic, the shortage of replacement sensors was a BIG deal. But, not so much anymore. That was the real reason the short derate time was painful…perfectly working system with a bad sensor killed the vehicle. For truckers, a huge income hit.
Complete agree. I spent just over $4k to tow my rig home and wait for a new sensor head. I would have driven it if I thought I could go 500 miles without a derate so I opted to tow. Zero chance I will ever run out of DEF, not any more than running out of fuel. Not my style.
Cheers Mikal.
Once again, the problem is not running out of DEF but the failure of the sensors in the DEF system that can get you limited to 5 MPH in the middle of nowhere even with a full DEF tank. The old rule was stupid and can get you in a very dangerous situation, for you and those driving near you. The new guidance makes sense.
That’s great news but the questions I have is when does it go into effect and when can us older RV’s get our units updated.
It’s not only when DEF fluids run low, but when sensors go bad. I have a Nissan Titan XD Diesel. After about 15,000 miles, the sensor in the DEF tank went bad. You can’t just replace the sensor, you must replace the whole tank. Then a few years later, the NOX sensor went bad. Both times I got the warning that I could only drive 200 miles. I had to wait a few days to get both sensors replaced. If you’re heading home from vacation and towing a trailer, that could be a big issue. Thanks to the new EPA Administrator for thinking of us.