Wednesday, December 7, 2022


Cummins comes through: A DEF sensor software patch now available


By Russ and Tiña De Maris
While the shortage of microchips has turned auto manufacturing upside down, RVers, too have been hit. If you’ve been following our coverage about how so many RVers have been stranded by DEF (diesel exhaust fluid) sensor failures, you know we’ve been harping on industry to come up with at least a temporary fix. We wrote early this month that Cummins, the EPA, and other industry types had announced they would allow a software patch. That patch would allow affected rigs to get back on the road, even before microchips could “ride to the rescue.” At the time, we wondered how long it would take for the software patch to materialize.

It seems the answer is – nearly a month. But we’re happy to report that Cummins is now issuing the temporary fix to “eligible” Cummins engine owners. Here’s how it works.

First, you have to qualify

Cummins, other industry interests, and the EPA have agreed on what they’re calling “a temporary calibration” to be loaded into Cummins’ engine control systems. We say “eligible” engine owners, because not everyone with a Cummins engine under the hood will be able to get the software patch. How do you know if you qualify?

First, your vehicle must already be disabled, that is, with the DEF system warning light showing up on your dashboard. If you’ve been hiding at home in the driveway, fearing to take your motorhome out on a trip lest it break down, hear this: If your DEF light isn’t illuminated, you don’t qualify for the patch.

Another condition may also rule out the software patch. Not all DEF sensor manufacturers are “fresh out” of DEF sensors. Cummins will NOT be able to provide the software patch UNLESS the DEF head in your rig is one that can just be readily replaced because of a shortage. How do you know where you stand? Here’s the official word from Cummins: “We encourage [owners] to inquire by emailing and include their engine serial numbers when emailing. For those OEMs that are not currently participating, we encourage customers to reach out to their vehicle manufacturer to secure a DEF sensor replacement because Cummins is not permitted to provide the calibration fix.”

A couple of hoops to go through

Here are some “ifs.” If your DEF system is already displaying an error message, and if your DEF head manufacturer can’t supply a replacement, then you can probably get the software patch. How do you do it? Ensure that you’re on the “OK list” by sending off an email to Cummins. Next, schedule an appointment with a service facility. Cummins has provided an internet link to a system where you can locate facilities anywhere in the U.S.

How much will it cost you? To Cummins’ credit, the software patch installation is a freebie. We’re hopeful that the lineup to get in and get the job done will be short, and hopefully painless. Once the patch is in place, the engine de-rate that has grounded so many will go away. Be alert though. You’ll have to manually check your DEF levels, as you won’t get any warning that you’re low on DEF. If you run your rig without DEF, you’ll soon be de-rated and in a world of hurt.

California “fly in the ointment”?

There is one more possible “fly in the ointment.” Here’s a quote from an email from Cummins to a reader. “Once the supply of DEF sensors becomes available, you will be contacted and required to make a service appointment to replace the DEF sensor and restore the original engine calibration. Please note, once the replacement parts are available, the repairs must be completed as the vehicle cannot be operated in the state of California without the original engine calibration.”

Let’s read that r-e-a-l  s-l-o-w. “The vehicle cannot be operated in the state of California without the original engine calibration.” It was too late in the news cycle for us to clarify this statement. Has California not signed up for this software patch? Does it mean those who do get the software patch best stay out of California until they have a new DEF sensor? Meaning they’d be violating the law? We’re not entirely clear on this, but we’ll update you once we know for sure.

And for those who may not qualify

DEF sensor work-aroundWhat about those of you who haven’t received the dreaded DEF sensor of death dashboard denunciation. Fearful of leaving the yard, lest you de-rate your diesel and end up in the ditch? We’ll point you back to the alternative DEF Sensor Simulator. If you build one, keep it with you. If your warning light comes on, plug it in. You can then go merrily on your way until you can get the software patch.

We’re happy that Cummins has stepped up to the plate with the software patch. But we’re still of this mind: The reason they did so is that the RV community kept after them to get off the dime. There is power in your words.


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

Edit note: Included working link to Cummins locator service. 9/26/21 1048hrs


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Lyndon Stiffler
9 months ago

I’m thinking my shut down was due to ice in my DEF tank:) the sensor couldn’t read fluid level. Let me just put this out. Every fluid in all vehicles now and has been always freeze proof to what like 20 to 30 degrees below zero????
So imagine my surprise when I found out DEF starts freezing at 12 degrees above zero 🤬
DEF in all Diesle’s has been mostly problematic since it was it was politically put in place by government.
Many people don’t know but the DEF fluid Paton is owned by NANCY PELOSI California’s biggest problem.

6 months ago

Where can I find articles about Nancy Pelosi owning DEF fluid patent or other government officials owning DEF fluid patent or raping for profits?

RV Staff(@rvstaff)
6 months ago
Reply to  smkraft

Hi, smkraft. Just for kicks I Googled the patent on DEF fluid. Here’s a link to information on it: I don’t see Nancy Pelosi’s name on there anywhere. 😆 Have a good night. 😀 –Diane

Jim L.
1 year ago

I purchase used moho’s for a large RV dealer. I have been sidelined twice recently because of the DEF problem. Once towed into Oklahoma City where it sat for 2 weeks waiting for a part. This last time I limped into a Cummins shop in Amarillo where they reprogrammed “the fix”. The fix lasted about 500 miles and it began the derating process again. At that point I was 40 miles from home base but I made it back. Perhaps I should carry one of those software plugin kits.

Darin Severns
1 year ago

Thanks again for all of your efforts on this issue. I am on my first replacement DEF head and will be driving to CA from KCMO in a few weeks. I hope I don’t have to play “find the Cummins dealer that actually has the patch and can do it” dance on the way there, but at least it exists! Great work.

1 year ago

Well that’s good but…What is someone suppose to do when your 500 miles from the nearest Cummins dealer? I don’t plan my trips around Cummins locations! So Cummins only went half way. Again, we the people get screwed.

John A Battistoni
1 year ago

Thank you for your pursuit of this solution and getting the attention of the ‘right people’.
Your handling and effort related to this effort, is a huge WIN for all of us.

From the bottom of my grateful heart, thank you for all that you have done getting this solution pushed through.

1 year ago

I think you guys are inflating your ego a bit that it’s only RVers that pushed this through. What about the fleets of 18 wheelers that can’t get UQS sensors? Don’t think their fleet managers weren’t yelling at their suppliers?

Paul Smith
1 year ago
Reply to  Kevin

My understanding was that the trucking industry was a) getting first dibs on whatever supply was available and b) not willing to expend the political capital to get an EPA waiver. In early June the EPA told me that the truckers had not yet asked for a waiver. The conventional wisdom was they didn’t think a waiver was possible so why bother. In early June the EPA was vaguely aware of the problem calling it a “mess” but they had no data about how big the problem was for RVers or truckers. To the best of my knowledge I was the first to formally petition the EPA for a waiver on June 23, I personally posted about the RV communities efforts on trucker forums hoping to get some attention because I though they would have more leverage. I never got traction. It wasn’t until the RV community made a bunch of noise that things started moving. If not for the RV community making pests of themselves I doubt there would be a solution today. Of all people I would know.

1 year ago

Is this a Cummins only issue? What about other Diesel engines such as my Mercedes Benz?

Greg Surratt
1 year ago

I’ve seen articles on FreightWaves that this DEF sensor issue is also affecting the trucking industry, contributing to shortages of consumer products along with the driver shortages and port congestion.

1 year ago

I’d just go with the sensor simulator. Why mess with Cummins, etc?

Bill Semion
1 year ago

All modern diesels have the same issue eventually. What about the others?

1 year ago

So I have to breakdown in the middle of nowhere and maybe towed a hundred miles to get the temporary software ! That’s reassuring, not !!!!!! Typical, idiots left a lot of people exposed

Bill Wooginowski
1 year ago

California has a law pertaining to outlawing system tuning. In most cases this tuning reduces mileage and impact emissions. If an RV has been tuned, it must revert back to the factory tune before the Cummins fix can be applied. Since the fix is coming from Cummins it would be considered a factory setting.

1 year ago

Wrong, it’s a Def sensor issue so they tweak emissions settings as a bypass. Meaning these vehicles will be polluting more than factory software vehicles.

Keith B
1 year ago
Reply to  Bob

Can you explain what you mean by “these vehicles will be polluting more than factory software vehicles”? How are they going to pollute more?

Marc Rodstein
1 year ago
Reply to  Bob

How do you conclude that they will be more polluting? If the problem is the “alarm” sensors wrongly reporting a problem and is not in the exhaust treatment system, the vehicle’s pollution would be no different than 10 minutes before, when the sensors were working.

1 year ago

Great job everyone!

Not affected by this but still sent emails and texts to help out.

Wondering how owners are supposed to get in for service if they are already in limp mode?

BTW what clown decided limp mode was appropriate for any issue that is not a serious IMMEDIATE safety or mechanical damage issue!

1 year ago

How is the patch applied?

1 year ago
Reply to  Rich

Like a software update I’m sure.

Dave Pellegrino
1 year ago

Bravo Zulu to Russ & Tina, RV Travel and all else who had a hand in moving mountains….

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