Wednesday, November 29, 2023


It’s out there – a DEF sensor workaround

By Russ and Tiña De Maris
If you’ve been following the saga of stranded RVers, it reads like a Shakespeare tragedy. But unlike the outcomes for Cleopatra or Macbeth, some of you may find light at the end of story. A group of intrepid, like-minded, never-say-die RVers in two months have put together a solution that some may find gets their RVs on the road again. From all appearances, it’s a failed DEF sensor workaround.

Not a moment too soon

For some, it couldn’t come a moment too soon. A couple of weeks ago we wrote that the EPA (Environmental Protection Agency) and diesel engine manufacturers had come up with a “fix” of their own. In our opinion, the fix wasn’t their idea. It was, rather, the result of bombardment by RVers and others affected by the DEF sensor debacle. Admittedly, a world-wide shortage of microchips has exacerbated the situation. But not until the EPA and industry were bullied a bit by RVers who’d been sidelined by the problem did they ever come to the decision to take action. Action, we add, that was originally suggested by RVers themselves. Their suggestion was to simply write a piece of software code that would allow rigs with defective DEF sensors to continue to operate without the mandatory “de-rating” that would slow them down to a snail’s pace five miles per hour.

The government solution? A statement issued by the EPA says, in part, “The Engine Manufacturers Association (EMA) on behalf of its member companies has proposed an industry wide approach that would provide a software solution for vehicles with failed parts to enable them to operate temporarily while the industry works to produce more replacement parts and that, long term, would provide replacement parts through a recall program … The manufacturers must still develop new software code and test it to ensure the software can be installed on vehicles in the field. The companies expect that they will be able to begin fixing some vehicles with failed sensors as soon as this week.” Yeah, you read it right: a software patch – just like RVers had suggested on their own.

Cummins’ talk: “An appropriate time”

That EPA statement was issued 11 days ago. To date, we’ve not heard of any engine manufacturer, Cummins or other, who has come forward to fix ANY vehicles. Last Friday one of our readers received this statement from John Tyner, Cummins’ “Customer Advocacy Leader”: “We are awaiting full approval of the regulatory agencies and are working on the communication strategy in tandem. You will receive a communication at the appropriate time according to the strategy determined between Cummins and the OEMs.”

While Cummins, the EPA, and others were hearing cries from sidelined RVers and apparently dragging their feet, other RVers weren’t just sending emails to them. They were working behind the scenes to come up with a solution. From all over the country, these folks heard about the problem and found each other on the internet. Many of them were tech-savvy, and in less than two months, working peacefully together, they developed a practical DEF-sensor workaround. It didn’t require a boatload of money, nor near-fistfights over approaches. In the end, the efforts of their labor won’t be garnering them motorhomes full of cash. Today, their DEF-sensor simulator is being released free to the public.

What’s it do?

What is a DEF sensor simulator? Simply put, it’s an electronic device that plugs into your RV. If your DEF sensor has gone bad and is telling your engine computer that something is wrong with the DEF system, the engine computer will send you into de-rate mode. If you’ve experienced it, you know it means trouble. You’ll soon lose engine power, and you’ll be forced to get off the road. You’re stuck waiting until whenever parts become available.

The DEF sensor simulator tells the engine that all is well with the DEF system. As a result, the engine computer won’t take that nasty de-rate action. Yes, you’ll need to keep DEF in the system. And you’ll need to check it manually, as you won’t be getting a warning that your DEF level is low. Once the EPA and industry get it together, you can get their software patch – then hope that parts become available soon.

Easy to follow

The DEF sensor workaround group has set up a website that’s rich with easy-to-follow instructions, videos, photos, diagrams, and part sources. Anyone can access the website. You don’t need a membership, and you won’t need a VISA card to get the information you need. What do you need? Here’s a lift from the “Quick Build” page:

“While there are many variations of hardware and software for this project, this page focuses on one method that is proven to work on the majority of tested motorhomes and endeavors to keep the construction process as straightforward as possible.

“Only basic electrical and DIY skills are required for the hardware assembly, no soldering is needed. The software installation in this procedure requires a Windows system and only involves typing some simple commands.”

Run into trouble? You’ll be able to contact the developers for advice in getting a working DEF sensor simulator.


To those who charge that this DEF sensor workaround is illegal, here’s a statement from the development group: “Modifying emissions systems to defeat their purpose is not legal. The DSS [DEF Sensor Simulator] is NOT a means to defeat the DEF system, a DEF system ‘Delete’ or in any way provide a means to discontinue use of the emissions system on your diesel powered equipment.” The developers are not offering any legal advice, as they say this should be viewed as a temporary fix. They strongly recommend that users get a new sensor when available or to take advantage of the Cummins solution as soon as possible.

So how can you get the information you need to build and install this DEF sensor workaround? Here’s the link to the DEF Sensor Simulator webpage.

One final note. If you’re somebody who’s retired from their “old job” and feeling a bit like the horse that’s been put out to pasture, think about this. The folks that developed this simulator that may help hundreds, if not thousands, of RVers out of a jam are not 30-something techies. They have an average age above 60. Look around. There may be ways you can put your skills to work for others, too.


RVers stranded with bad DEF sensors. What does this mean? Are you affected?

EPA speaks out on failed DEF heads, promises relief – but when?


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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RIVAN54 (@guest_236887)
6 months ago

I own a 2017/16 TIFFIN ALLEGRO 32BR. It is presently at Cummins for repairs, the SCR has failed again for the second time and parts are not available, when? Who knows! I also had 🛑 ENGINE LIGHT inside UHAUL storage and was De-rated, had to replace the Tank Sensor $1400 from Tiffin and then was able to travel to Cummins for repairs . I have a motorhome that has approximately 32000 miles and have spent 45 days in the shop, Cummins and Tiffin discontinued this 5.0ISV ENGINE and are reluctant to help in any capacity. They new the problem with the DEFF/SCR SYSTEM was and is a failure. IF ANYONE HAS PROBLEMS WITH THIS MODEL. Please post it. I’m getting ready to USE THE LEMON LAW if it helps. I’m tired of not enjoying this motorhome and I don’t have the funds to buy another.

Mike Oates (@guest_201903)
1 year ago

I see the tons of info for Cummins engines. Is there anything for us Ford 6.7 Powerstroke engines? I tow a camper and dont want to have the problems with the derate.

John Pierce (@guest_201558)
1 year ago

This happened to me recently on a trip coming back from Telluride to Denver. I saw a weird error message saying power was being reduced because of an “error” — not descriptive at all. I thought it might be a regen, but it sounds like it was this DEF sensor issue.

I was pulling my Escape 21′ foot camper with my 2021 GMC Canyon AT4 duramax. For about an hour it reduced my maximum speed to about 25mph. We were kind of out in the middle of nowhere when it happened. When we reached Grand Junction, we stopped for fuel and lunch and I was hoping it would resolve. When I started my truck I saw the error again, but this time it let me maintain highway speed and I made it home to Denver with no further issues. The error showed up every time I started my truck for a couple of days and then disappeared.

I had a nearly full tank of DEF when all this happened.

Does anyone know if this DEF simulation fix will work on the baby duramax? This was SUPER stressful!!

Ronald Johnson (@guest_182435)
1 year ago

Also, a master/slave NOx sensor set. To simulate it would have to generate some level of plausibility maybe by watching the DEF injector and SCR temps. Again, not to defeat the system but be able to get the thing somewhere to get parts. Oh, and cummins prices for the Chinese sensors are SKY high.

Recently had a PACCAR fail and it had codes 3714 and 3712. If you get these codes they can go on to reciprocate themselves requiring a complete ‘calibration’. No one wants to work on these trucks either due to Davie4 and Insite software requirement. The temperatures these system achieve in less than friendly environments means broken marman clamps, corroded DEF injectors and gaskets.

When the DEF system actually works that exhaust comes out clean as a whistle.

Cummins Repower Guy (@guest_161951)
1 year ago

Did you know all Emergency Vehicle’s with Cummins Engines have a (NON DERATE PROGAMMED ECM) No matter what gets mad or fails to a point they WILL NOT DERATE. Imagine fighting a fire with the water hose, engine screaming and it goes to idle because the DEF sensor is mad!! 🤯 I hope this helps someone’s defense. There is usually a cure but there wouldn’t be any money in a cure it’s the treatment for all that’s it $$$$ I would be happy to help anyone needing guidance with there rv if your around orange county CA. I have the tools RICH and I can make you a cable I have lots of j1939 data cable and Deutsch connectors.

Rich (@guest_149787)
2 years ago

Be aware…after purchasing the parts to do this, (and realizing that I ordered the wrong cable), this will not be easy to do with a Freightliner chassis. The plug has to be manually put together and special tools are needed. I also think that training and/or experience is needed in this area to accomplish this with confidence and not burn something out on your motor home. As expensive as repairs are, I cannot risk any errors.

I am sure there are folks out there who can do this in their sleep, but I am not one of them. I would advise anyone who wants to do this, to thoroughly read all instructions before purchasing these parts.

I will be reaching out to the vendors to see what I can return as much of it I did not open.

I have learned my lesson and will not waste my money again.

Just beware!

Keith B (@guest_149846)
2 years ago
Reply to  Rich

Hi Rich. I’m truly sorry if you bought components and then decided you couldn’t build the device. If you just post what you have and what you want for it either here, on one of the discussion threads at IRV2.COM or at the boards someone will be happy to take it off your hands. While the original suggested hardware quickly sold out and the vendor quickly raised the price (the developers have no relationship whatsoever with any of the vendors. We provide information, advice and free software) we have since tested and recommended alternatives with each iteration getting less expensive. The current preferred circuit board is available for less than $20. There are detailed instructions for how to put each alternative together. That includes the Freightliner-compatible connector which can be, and has been, assembled with no tools other than a crimping tool but even a set of pliers will work.
Do you feel that you were misled in any way?

Tim Hardy (@guest_200774)
1 year ago
Reply to  Keith B

Ham radio operators frequently use Raspberry Pi and Arduino boards for projects. A Ham Radio store/supplier might be a ready source of boards and other hardware.

George (@guest_142853)
2 years ago

Delete it!!!

Bob M (@guest_142771)
2 years ago

Those who worked on developing the DEF Sensor workaround need to be commended and thanked. We can’t count on our government officials and politicians.

Drew (@guest_142708)
2 years ago

This sure is welcomed news, thanks to everyone who was involved.

Wolfe (@guest_142696)
2 years ago

I was going to complain about the jab at 30something techies …and then realized i’m about 50 myself…crap! And yeah, us old guys still have serious tech value since the “kids” i work with think “LoL” components are funny instead of “Loss of Life”-critical, and get lost when military hardware doesn’t have a web page.

Hearing about the failed sensor issue, I immediately thought “couldn’t someone spoof the sensor with an arduino… pretty simple I think…” so it’s amusing they called it a simulator but otherwise did exactly what i’m thinking.

As for legality… $&@$^*%! lawyers. Its your property and life. I’m all for the environment so fix it when you can, but this isn’t something law should ever get involved with – find “DEF Sensor” in the Constitution. I CAN find plenty of freedom and non- interference references, and that’s the only law that applies.

Uncle Mike (@guest_142793)
2 years ago
Reply to  Wolfe

You can tell the project is run by adults because the authors write clearly, in complete sentences, and without emojis. Nice to know that technical competence, along with an ability to communicate in writing still exists.

Chris Mead (@guest_142689)
2 years ago

Russ has been all over this since the beginning. Thank God for a free press.

Paul Smith (@guest_142699)
2 years ago
Reply to  Chris Mead

I’ll second that. Thank you Russ and RVtravel.

RV Staff
2 years ago
Reply to  Chris Mead

Thanks, Chris. Yes, Russ and Tina are doing a terrific job on this topic! Lots and lots of time and research. Thanks, Russ and Tina! 🙂 –Diane

1HasBeen (@guest_142662)
2 years ago

Don’t hold your breath waiting on Cummins. They have gone 100% “woke”, and Linebarger is too busy delving into political issues, and signing onto “woke” letters to the government to worry about diesel engines, or the folks who rely on them.

Thomas D (@guest_142661)
2 years ago

How about my 2011 chev duramax? First year def was used in GM vehicles. A LOT of trouble.

William Semion (@guest_142646)
2 years ago

How does this apply to other owners of other Diesel engine systems?

Glenn stimpson (@guest_142835)
2 years ago
Reply to  William Semion

I have a Ford transit powerstroke diesel in a 23′ Thor gemini. Def low fluid light came on, & added 21/2 gal Def fluid, however, warning never went away. I paid it no attention until warning came on that in 35 miles, I would be slowed to 49mph. I added 4 Gallons of Def at that time, but at 36 miles, I was limited to 49 mph! After many calls, a Ford dealer told me they would “work me in”.– after 2 days at dealership, they told me they had replaced the Def pump, & a wiring harness & the cost was $1356.00, I paid it, & was happy to be on my way!
How will I ever know what the truth was? I’m stunned to find it may be a common problem! (Cummings told me they didn’t have Ford codes, & could not work on my powerstroke!)

Bob (@guest_144887)
2 years ago
Reply to  Glenn stimpson

Why did the extended Ford DEF warranty not kick in. No way you should have paid for this.

tom (@guest_142570)
2 years ago

Crowd sourcing at work. Government inaction at work. Pick your poison.

Tommy Molnar (@guest_142607)
2 years ago
Reply to  tom

RV’ers taking matters into their own hands. I love it.

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