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Old 02-07-2022, 11:48 AM   #1
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Fuel gauge and DEF guage incorrect

On our trip from VA to FLA the fuel guage was inaccurate and the DEF guage never left full for 700 Mike's. Of course I filled both every 300 miles. I'm thinking a ground issue. Any suggestions?
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Old 02-07-2022, 02:08 PM   #2
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On our trip from VA to FLA the fuel guage was inaccurate and the DEF guage never left full for 700 Mike's. Of course I filled both every 300 miles. I'm thinking a ground issue. Any suggestions?
All I see is you have a diesel. Is the problem with the tow vehicle? Or do you have a diesel class C or A?
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Old 02-07-2022, 02:24 PM   #3
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On our trip from VA to FLA the fuel guage was inaccurate and the DEF guage never left full for 700 Mike's. Of course I filled both every 300 miles. I'm thinking a ground issue. Any suggestions?
The fuel gauge on the M2 chassis is known to be inaccurate, even Freightliner says "nothing we can do". A few customers had the sending unit replaced but reportedly it didn't help much. The sending unit is only in the driver's side tank, but when you did get fuel did the tanks seem close in their levels? Our rigs use the "Equiflo" system to even out the tank levels, there is no crossover line like trucks used to have. Too prone to damage from road debris causing an (expensive) environmental mess. So if the two tanks are significantly different in level when you stop there might be an issue affecting the Equiflo system. Now understand the driver's side tank is 6 gallons smaller than the passenger side (the DEF tank takes up room) so gallon-wise I always have to add less on the driver's side compared to my passenger side. The Equiflo balances fuel level, not quantity. So a given level is more gallons in the passenger side tank.

Now the DEF gauge is a different story. I've not heard of any other Seneca owners complaining about that issue. Not that it hasn't happened, just not something I have seen here or the two Facebook Seneca groups I participate in. I am assuming your DEF system is working since it is consuming fluid and you did not mention any warning lights or a derate. You certainly would be aware of a derate, 5mph down the road gets everyone's attention!
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Old 02-07-2022, 02:25 PM   #4
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2016 Seneca HJ, 6.7 CUMMINS
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Old 02-07-2022, 02:29 PM   #5
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2016 Seneca HJ, 6.7 CUMMINS
That's a M2 chassis.
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Old 02-07-2022, 02:50 PM   #6
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I can not speak to anything on the fuel gauge. However on the def gauge and this may not apply at all to your chassis as I have no idea on the setup but I can say on my 2017 ram with the 6.7 the def tank is well known not to come off full for well over a gallon and with a 5.5 gal tank you go through approx 20% of the tank capacity before it even moves off of full. I can say that even towing our fiver with that truck 300 miles would not be enough to budge the gauge if it was full as even towing I could get around 400 miles per gallon of def. My 22 ram does not do this it is much more linear still somewhat top heavy but nothing like the 17.

I realize the applications are entirely different but just wanted to throw it out there as a possibility
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Old 02-07-2022, 03:09 PM   #7
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I can not speak to anything on the fuel gauge. However on the def gauge and this may not apply at all to your chassis as I have no idea on the setup but I can say on my 2017 ram with the 6.7 the def tank is well known not to come off full for well over a gallon and with a 5.5 gal tank you go through approx 20% of the tank capacity before it even moves off of full.
Good post, also true with a 2019 Ram 6.7. Traveling in the mountains last summer, Idaho, Colorado, Utah, back down to Vegas I used 7/1/2 gallons of DEF around 5500 miles. Seems excessive, but that's what it was. Round trip from Michigan's Upper Peninsula around 5500 miles.
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Old 02-08-2022, 06:00 AM   #8
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Yes it is consuming DEF at its normal rate. No other DEF issues have occurred. Thanks for your input. I'm gonna get under it today just to make sure I didn't knock a wire off the sensor.
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Old 02-08-2022, 06:51 AM   #9
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Yes it is consuming DEF at its normal rate. No other DEF issues have occurred. Thanks for your input. I'm gonna get under it today just to make sure I didn't knock a wire off the sensor.
I did a little digging last night and did find a Freightliner Service Bulletin 49-32 that is applicable to the M2 chassis as well as other Freightliner models. Might be helpful in your troubleshooting.

https://static.nhtsa.gov/odi/tsbs/20...46782-4930.pdf
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Old 02-08-2022, 07:57 AM   #10
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On our trip from VA to FLA the fuel guage was inaccurate and the DEF guage never left full for 700 Mike's. Of course I filled both every 300 miles. I'm thinking a ground issue. Any suggestions?
Normal DEF consumption for our rigs is supposed to be 2% per gallon of diesel consumed. So, you would expect to consume only 1.5 gallons of DEF for a full load (75 gal) of diesel. As you stated, you are topping off the DEF tank every 300 miles (30-35 gal of diesel consumed, roughly). That would be about .6-.7 gal of DEF consumed. I would expect the gauge not to move.
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Old 02-08-2022, 12:55 PM   #11
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I normally fill up fuel at 350-450 miles and then fill DEF every other fill. I usually have one or two lights out on the def gauge. I seldom see one light out before 300 miles after def fill.
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Old 02-08-2022, 06:00 PM   #12
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Something I noticed in the first 1k miles of owning our '22 Seneca (S2RV). The DEF gauge is 4 LED's. Even if 3/4 LED's are lit indicating 75%, it may be just above 50%. Seems like the actual fluid level in the tank has to hit the the next lower quartile before it turns off the corresponding LED. That, and it might have a little room at the top of the tank too. Seems to take a long while for that first light to turn off and indicate 3/4 tank DEF left.
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Old 02-08-2022, 07:23 PM   #13
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Something I noticed in the first 1k miles of owning our '22 Seneca (S2RV). The DEF gauge is 4 LED's. Even if 3/4 LED's are lit indicating 75%, it may be just above 50%. Seems like the actual fluid level in the tank has to hit the the next lower quartile before it turns off the corresponding LED. That, and it might have a little room at the top of the tank too. Seems to take a long while for that first light to turn off and indicate 3/4 tank DEF left.
Yep, another reason I love my Bluefire module and dash, the DEF guide on it reads like a gas gauge and has the actual percentage level on it.
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Old 02-09-2022, 06:03 AM   #14
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Thanks, appreciate the feedback. Be safe out there.
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Old 02-16-2022, 02:57 PM   #15
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Good post, also true with a 2019 Ram 6.7. Traveling in the mountains last summer, Idaho, Colorado, Utah, back down to Vegas I used 7/1/2 gallons of DEF around 5500 miles. Seems excessive, but that's what it was. Round trip from Michigan's Upper Peninsula around 5500 miles.
My 2016 Ram sucks def when pulling my 5rh wheel but when empty I thought my gauge was broken. Big difference in consumption
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Old 02-16-2022, 03:42 PM   #16
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I can not speak to anything on the fuel gauge. However on the def gauge and this may not apply at all to your chassis as I have no idea on the setup but I can say on my 2017 ram with the 6.7 the def tank is well known not to come off full for well over a gallon and with a 5.5 gal tank you go through approx 20% of the tank capacity before it even moves off of full. I can say that even towing our fiver with that truck 300 miles would not be enough to budge the gauge if it was full as even towing I could get around 400 miles per gallon of def. My 22 ram does not do this it is much more linear still somewhat top heavy but nothing like the 17.

I realize the applications are entirely different but just wanted to throw it out there as a possibility
The gauge in the DEF tank ( at least on my 2016 RAM ) is not a float type gauge like in the fuel tank. It is some sort of sensor strip attached to the pump module in the tank. And that does not reach the top of the tank. So as you say, you need to burn about 20% of the DEF volume before it even touches the top of that strip ( which will now indicate FULL, even though you're NOT full ).
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Old 02-16-2022, 04:20 PM   #17
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The gauge in the DEF tank ( at least on my 2016 RAM ) is not a float type gauge like in the fuel tank.
It is a float in the OP's 2016 Freightliner M2 Seneca.
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Old 02-16-2022, 04:45 PM   #18
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I can not speak to anything on the fuel gauge. However on the def gauge and this may not apply at all to your chassis as I have no idea on the setup but I can say on my 2017 ram with the 6.7 the def tank is well known not to come off full for well over a gallon and with a 5.5 gal tank you go through approx 20% of the tank capacity before it even moves off of full. I can say that even towing our fiver with that truck 300 miles would not be enough to budge the gauge if it was full as even towing I could get around 400 miles per gallon of def. My 22 ram does not do this it is much more linear still somewhat top heavy but nothing like the 17.

I realize the applications are entirely different but just wanted to throw it out there as a possibility
I'm going to add my 2 cents worth here as well. I have a 18 Ram 2500 with the 6.7 and summer of 2020, we towed our Jayco hybrid from California to South Dakota. I filled my DEF tank before departing home. We ran 65 or so most of the way to SD. Drove around for a week before heading for home. DEF Gauge read half. I added a 2.5 gallon jug and it filled the tank. We drive from SD to Hill AFB in Ogden UT. On that run, I was buck a 30 mph headwind most of the way across Wyoming. We got to Hill and the DEF gauge was back to half. Added another 2.5 gallon jug and drove the rest of the way home. When we got home, DEF gauge was reading 3/4. Talking with some trusted diesel techs, I became informed of a few details. The DEF system will use more fluid the harder the engine is working. And two; treat DEF like milk, it will go bad it left stored too long. As such, I was advised to only add DEF when the low fluid light comes on. I have noticed that even though Ram says the tanks holds 5.5 gallons, and when the light comes on you should be able to add 5 gallons. I've 50 miles and 100 miles after the low fluid light came on and added 2 jugs and overflowed the tank both times. Since then, I've decided that when the light comes on, I'm only adding 1 jug. Doing that brings the gauge to 3/4. When I'm at home, I buy DEF, 1 jug at a time. When we're leaving for a trip, I'll top off the tank before leaving home and take 4 or 5 jugs with me. I'm starting to rethink that as many truck stops now have DEF at the pump for less than what I can buy it for even at work.
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Old 02-16-2022, 06:41 PM   #19
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Thanks Rob and gang. I may be over thinking the DEF guage.
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