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Old 08-02-2021, 08:03 AM   #1
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Another Cummins DEF problem looming.

Contributing to the DEF sensor failure in Cummins engines is a view that doing the normal Quick Start of these engines is a partial or major reason for the sensors seeming to fail. Apparently the ECU logic needs to know that all the sensors are present and reporting correctly before the software can trigger an emissions "OK" message. So, if you jump in your coach, hit the brake and punch the button, its possible (or even probable) that the emissions sensors including and particularly the DEF sensor will not have reported in before the starter goes to work. Eventually this will lead to an ECU triggered elimination of the presence of the DEF head sensor which in turn will trigger a limp mode protocol and you are effectively stuck.

The answer for now seems to be, keep you foot off the brake, punch the button once and get the system energized, then punch it again and wait for the engine ECL light to extinguish. Now the ECU is ready and all the sensors have been detected and found reporting good data. Now put you foot on the brake and start the engine. Do this EVERY TIME not just the initial start of the day, season, or whatever.

In the meantime no one else that drives your coach cares, knows or is bothered by a problem that may never happen so do not expect Dynamax, your shop or dealer to do this until so ordered by Cummins/RAM which is not likely to happen until the litigation/EPA has been completed in (say) three years and another software recall is issued.

I should add that this is all hearsay and another curse or blessing courtesy of the Internet. But it seems that the Class A Cummins folks with the same ECU systems that we have in the Isata and other FR products, have been so extensively affected by these Limp Mode transitions, that matter has bubbled to the surface the way Internet ground swell seems to when there is a "smoke vs fire" process. SYMMV.
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Old 08-02-2021, 08:10 AM   #2
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good info and seem logical
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Old 08-02-2021, 08:48 AM   #3
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We will follow your advise to avoid "Limp Mode", thank you.
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Old 08-02-2021, 09:07 AM   #4
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We will follow your advise to avoid "Limp Mode", thank you.
Not my advice - just an Internet consensus. There are lots out there that say they have been starting their 2019+ Cummins diesels by kicking the tires and lighting the fires since 2019 and are not going to change ( or get vaccinated ) but there are also a significant number whose coaches are essentially side lined waiting for new DEF sensor heads which are not available.

They have deluged their Congressional reps, the EPA, NHSA, and the BoD of Cummins to the extent that they are getting responses. So this is a BIG ISSUE - but from the silence on this forum may not have Isata or DX applicability.

I do not pretend to know the answer - just reporting the news - which could be fake...
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Old 08-02-2021, 12:32 PM   #5
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Thanks for the suggestion. I don't have a Cummins motorhome, but I will do this with my Cummins truck to possibly avoid the same issue.
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Old 08-02-2021, 01:11 PM   #6
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Is this an issue on RAM P/U truck diesels?
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Old 08-02-2021, 01:17 PM   #7
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I will say that while the Class A's and C's share "some" motor/transmission combinations, they are vastly different in many ways.

FCCC builds the Class A's, different plant, different lots of things. Not saying it won't be the case, but I know on a Freightliner it won't even start until you have cycled the key...gauges sweep, then you can fire it up.

Ram 5500 not the same, but totally different animal than diesel pusher.
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Old 08-02-2021, 01:21 PM   #8
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I will say that while the Class A's and C's share "some" motor/transmission combinations, they are vastly different in many ways.

FCCC builds the Class A's, different plant, different lots of things. Not saying it won't be the case, but I know on a Freightliner it won't even start until you have cycled the key...gauges sweep, then you can fire it up.

Ram 5500 not the same, but totally different animal than diesel pusher.
That seems to fit the evidence to date inasmuch as I cannot find any firestorms on the RAM truck web sites. And those guys do not mince words in their comfort or discomfort with RAM and Cummins. I was expecting a sh1tstorm from them but nada...so far.
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Old 08-02-2021, 03:55 PM   #9
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I don't know, but there seems to be a lack of error checking in SW for cars. That said, a few more lines of code to verify each sensor when a missed signal happens is not too hard, but that is money. Just be glad aircraft is different.
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Old 08-02-2021, 04:22 PM   #10
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I don't know, but there seems to be a lack of error checking in SW for cars. That said, a few more lines of code to verify each sensor when a missed signal happens is not too hard, but that is money. Just be glad aircraft is different.
Aircraft are different and thus way more expensive. If autos were built to aerospace standards, the equivalent of a Lexus 450H would sell for $1.5 million plus at the equivalent volume. They are still revising the code for the F-35 and the B-787.
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Old 08-02-2021, 04:41 PM   #11
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You really think so?

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Originally Posted by SQROOT View Post
I don't know, but there seems to be a lack of error checking in SW for cars. That said, a few more lines of code to verify each sensor when a missed signal happens is not too hard, but that is money. Just be glad aircraft is different.
You really think so?

The crashes of the 737-MAX were caused by a failed angle-of-attack sensor that suddenly appeared as a change in pitch from nearly-level to 75-degrees-nose-up. Nothing in the software checked the previous reading to realize that it is physically impossible to move an aircraft from level to nearly vertical in between two samples milliseconds apart. And nothing in the software checked the other sensor on the other wing!

The fly-by-wire software decided the plane was really pitched up and forced the control yokes forward so strongly that both pilots pulling with all their strength could not overcome the resultant dive into the ocean.

Boeing's review of the software will take a couple of years to complete. Already several flaws in Boeing's development process AND the FAA's review process have been revealed.

Sadly, high-quality software is a dying art.
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Old 08-02-2021, 06:02 PM   #12
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Just me being anal, but I have owned at least one each of the big 3 diesels, and ALWAYS turn on ignition and wait for all the clicking and beeping to stop before starting engine. 10/15 seconds tops. I like to let the ECU/ECM wake up and get it's bearings before start up. Really angers DW when she is in a hurry. Just sayin!
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Old 08-02-2021, 10:10 PM   #13
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I was surprised at how quickly the truck started. I just thought it was quick glow plugs, my 2008 grand cherokee with the diesel engine was a very quick start as well, push button and it started. My 2017 ram 3500 takes a few seconds before it starts, guess I will play the acc game before starting the motorhome just in case.
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Old 08-02-2021, 11:13 PM   #14
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Just goes to show that even in AC there needs to be error checking.
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Old 08-05-2021, 08:26 AM   #15
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Quote:
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I was surprised at how quickly the truck started. I just thought it was quick glow plugs, my 2008 grand cherokee with the diesel engine was a very quick start as well, push button and it started. My 2017 ram 3500 takes a few seconds before it starts, guess I will play the acc game before starting the motorhome just in case.
FYI the cummins in the Ram chassis doesn't use glow plugs. It has a heating grid in the intake to warm the incoming air. It even will cycle that heater to preheat incoming combustion air when the engine is running.
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Old 08-12-2021, 06:19 PM   #16
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What sensor is the big issue?
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Old 08-12-2021, 06:46 PM   #17
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What sensor is the big issue?
Apparently 2: the one that detects whether there is enough DEF and occasionally another that detects the flow of DEF. Low cost items but unavailable at the moment.
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Old 08-12-2021, 07:30 PM   #18
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Quote:
Originally Posted by Larry-NC View Post
You really think so?

The crashes of the 737-MAX were caused by a failed angle-of-attack sensor that suddenly appeared as a change in pitch from nearly-level to 75-degrees-nose-up. Nothing in the software checked the previous reading to realize that it is physically impossible to move an aircraft from level to nearly vertical in between two samples milliseconds apart. And nothing in the software checked the other sensor on the other wing!

The fly-by-wire software decided the plane was really pitched up and forced the control yokes forward so strongly that both pilots pulling with all their strength could not overcome the resultant dive into the ocean.

Boeing's review of the software will take a couple of years to complete. Already several flaws in Boeing's development process AND the FAA's review process have been revealed.

Sadly, high-quality software is a dying art.
From what I read in the NTSB report was that both pilots violated Flight Deck Protocols in that they switched to manual to regain control of the aircraft and were successful, but then switched back to the automated system and lost total control. Once you go to manual due to a fault you don't go back automated.
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Old 08-12-2021, 07:32 PM   #19
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Apparently 2: the one that detects whether there is enough DEF and occasionally another that detects the flow of DEF. Low cost items but unavailable at the moment.
That's odd if people can't get the urea pump, just replaced one on a truck last week. Had the part the next day.
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Old 08-12-2021, 08:12 PM   #20
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Just got a DEF pump replaced, updated- 2 design. Truck marked OTR for 3 weeks. 2016 RAM 3500 @ 43K miles.
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