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Old 12-13-2019, 09:10 AM   #1
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Low def

Greetings.... looking for answers from FREIGHTLINER chassis owners only please.....

2017 Berkshire 38A, ISB340 It's COLD outside, as in 20's overnight. Def in the tank is less than 6 months old.

After a few miles from startup Low DEF warning on LBCU.... Gauge on the tank says 1/4. Two out of four green lights in the fuel gauge on. Amber engine outline warning light.

Have ordered DEF, will top off and see. However, I've been lower, much lower, with no warning. In fact I've never seen the warning.

Does anyone have SPECIFIC information, hopefully with a diagram or two, on the quantity sensing system?

Any other words of wisdom on THIS system.....? (No, I don't care about Aunt Millies tractor.... )

Thanks.
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Old 12-13-2019, 10:06 AM   #2
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if less than 3 years old it’s covered under warranty. Could be the DEF Header or the computer or both. For mine, the header was bad and replaced. IMO, the important part of it is to not let it freeze. If you have ever spilt some and when it dried you get that white powdery stuff. When it freezes and thaws, expands and turns to a solid, then thaws and turns back into liquid, it leaves all that white stuff, the urea on all the sensors inside the tank. I bought mine used from Minnesota. Yours says 1/4 tank, so adding may help. It helped mine while we where on the road, my tank was at 3/4 full, and a Gal and a half turned the low def light off. As mine is in storage it is below 1/4 tank. Nothing worse than your coach going in limp mode from a sensor.
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Old 12-13-2019, 10:20 AM   #3
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Quote:
Originally Posted by RWDJR. View Post
IMO, the important part of it is to not let it freeze.
Not much choice as I don't have a heated garage...... But thanks for the insight.
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Old 12-13-2019, 01:00 PM   #4
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I don’t either, that’s why I’ll keep it as low as I can while in storage.
Add a couple gallons and see what happens. The freezing idea is just my 2 cents. You don’t here about it much with semi’s, then run everyday. Pickups won’t freeze because the def is in a bladder in the fuel tank. My info on the freezing came from a large farmer who has newer equipment that sits during the winter months. Like I said earlier, as long as it’s under warranty, any Cummins or Freightliner shop that will work on RV’s will repair it. Mine was a 14xx.00 bill that was covered.
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Old 12-13-2019, 01:40 PM   #5
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Whats the critical low temp for def fluid?
1 more thing to add to the "had no idea about this owning a DP" list.
Im in myrtle beach until jan.15th. Has gotten down to low 30's a few nite but then back up during the day
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Old 12-13-2019, 02:07 PM   #6
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Oscarvan --

I have some discrepancies between my dash DEF gage and the tank gage. When the tank gage reads ~60% full, the dash gage still has three green lights. When the tank gage drops to ~40% full, the dash gage drops to two green lights at which time I pour a 2-1/2 jug of DEF into the tank to bring it back to near full.

With regards to DEF freezing, it has a freeze point of 12 F. If your motorhome is in the northern half of the U.S., then you may wan to take some action to help assure the DEF will not freeze. Cummins has a good Q&A document about DEF that is useful --> https://www.cumminsfiltration.com/africa/sites/cumminsfiltration.com.africa/files/MB10033.pdf

The fifth question on page 5 of the document states that SCR systems are designed to provide heat to keep the DEF system warm and/or thaw-out a frozen system.
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Old 12-13-2019, 02:38 PM   #7
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Same problem occurred with our 2017 Dutch Star, with a FL chassis, while traveling south this past January. Called FL when the “low def” activated. The Rep told us to stop ASAP since the engine may shut down. Eventually the red warning “Stop Engine” light came on. Coach was towed to a local FL dealer, where after waiting three days for the part, the “def head” (top of the tank) was replaced. FL concluded it was a defective def head, possibly impacted by the cold Michigan wind chill temps of 30 - 40 below. Additionally, I later learned this was a common problem this past winter. I plan on taking the following preventative measures: keep def in house where it will remain warm, erect a wind barrier around the rear of the coach, and depending on the temps, insert a small ceramic heater in the def tank bay. Note our coach is and was connected to shore power.
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Old 12-13-2019, 07:42 PM   #8
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Thanks for the replies. I'm at the house right now, but we're supposed to go on a trip in January. I assume that if the condition goes away, whatever it is, the fault will reset itself.....
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Old 12-13-2019, 08:20 PM   #9
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Quote:
Originally Posted by RWDJR. View Post
Pickups won’t freeze because the def is in a bladder in the fuel tank.
1: My Chevy 3500 had a separate tank for DEF.
2: The fuel tank is no warmer than ambient, at least on startup. The return fuel MAY raise the temp a little, but that's a big tank out there in the open.
3: The DEF tank on my coach is heated.
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Old 12-14-2019, 02:07 AM   #10
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OK, looking at the FCCC website it appears the Emissions warrantee is 5/50 not 3/50. I am well within 5/50. So maybe the 24/7 tech I spoke to this morning was ill informed.... I will call them again with the "evidence"....
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Old 12-14-2019, 05:43 AM   #11
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With respect to the concern about freezing:

“Q. How do I keep the DEF from freezing? What happens if the DEF freezes
in the tank on the vehicle?
A. During vehicle operation, SCR systems are designed to provide heating for the DEF tank and supply lines. If DEF freezes when the vehicle is shut down, start up and normal operation of the vehicle will not be inhibited. The SCR heating system is designed to quickly return the DEF to liquid form and the operation of the vehicle will not be impacted. The freezing and unthawing of DEF will not cause degradation of the product.”

Source: https://cumminsfiltration.com/sites/...es/MB10033.pdf
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Old 12-14-2019, 08:56 AM   #12
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In and of itself, I would not worry at all about DEF freezing. From top to bottom, the system is designed with the probability of freezing not causing a problem. in addition to the tank and line heaters already mentioned, the specific mixture of urea and water is what is known as a “eutectic” mixture. Meaning that as the mixture freezes, the water and urea contents freeze at the same rate (so the concentration of the remaining liquid does not change. Same for the reverse during melting).

Residual powder might be a problem ... when i fill my def tank, the readings read low for maybe a mile or so of driving ... but then “bounce up” to full. I have always put that down to the time it takes for the residual crystals on the float to dissolve, and allow the thing to freely slide upward.

In this case though, weird that your sensors indicate reasonable def level, yet the warning light is on. I am not sure if there is a separate sensor for the computer? If so it might be that sensor. Otherwise, my guess would be its the computer...
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Old 12-14-2019, 01:06 PM   #13
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The only issue I've seen is the DEF injector in the exhaust stream will crystal up when the unit sits... than it will not inject correctly and throws a code....

I hate the dealer and decided that maybe a search might lead to an answer... so I pulled the injector and found a gob of crystals at the end of the injector.... washed them off completely and than reinstalled...

I can't figure out how to force a fluid flow test.... with the injector hanging on the hose.... this would confirm good operation....

However I than put the thing back together and within a few starts the code dropped off... the light went out... and all's been good....

What I learned was to check this after the units been in storage for several months. just my 2 cents worth on what I've learned...
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Old 12-14-2019, 02:54 PM   #14
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Quote:
Originally Posted by jelag View Post
The only issue I've seen is the DEF injector in the exhaust stream will crystal up when the unit sits... than it will not inject correctly and throws a code....

I hate the dealer and decided that maybe a search might lead to an answer... so I pulled the injector and found a gob of crystals at the end of the injector.... washed them off completely and than reinstalled...

I can't figure out how to force a fluid flow test.... with the injector hanging on the hose.... this would confirm good operation....

However I than put the thing back together and within a few starts the code dropped off... the light went out... and all's been good....

What I learned was to check this after the units been in storage for several months. just my 2 cents worth on what I've learned...
Interesting..... any help as to where to find said injector? In the exhaust system I assume? Just follow the hose?
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