DEF Gauge A Bit Wacky.
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More Turbo
Joined: Aug 2005
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DEF Gauge A Bit Wacky.
I kept getting a message on the dash screen today that my DEF was getting low. First message said I could go around 500 miles. The gauge on the dash said I had just under 1/2 tank and my ForScan gauge said same thing. So right away I figure something isn't right.
I kept getting updates of that message throughout the day, each time saying I had fewer and fewer miles before I would be out of DEF. Meanwhile the gauges were going down slightly but never much past 1/2.
The last notice was that I had 99 miles to go and when I clicked "OK" to clear the message the DEF gauge suddenly dropped to almost empty. Wham - just like that; almost like some float in the DEF tank had been stuck at the half way point but suddenly dropped.
How weird is that? Gauges (both dash and ForScan) say no less than 40% but truck somehow knows the level is getting low. Huh??
And when I filled it, it only took just over 4 gallons and it says it's full. Go figure!
I already had a service appointment for another problem, so I guess I'll have this checked to.
Just wondering if anyone else has seen anything similar.
I kept getting updates of that message throughout the day, each time saying I had fewer and fewer miles before I would be out of DEF. Meanwhile the gauges were going down slightly but never much past 1/2.
The last notice was that I had 99 miles to go and when I clicked "OK" to clear the message the DEF gauge suddenly dropped to almost empty. Wham - just like that; almost like some float in the DEF tank had been stuck at the half way point but suddenly dropped.
How weird is that? Gauges (both dash and ForScan) say no less than 40% but truck somehow knows the level is getting low. Huh??
And when I filled it, it only took just over 4 gallons and it says it's full. Go figure!
I already had a service appointment for another problem, so I guess I'll have this checked to.
Just wondering if anyone else has seen anything similar.
Lead Driver
Joined: Nov 2005
Posts: 8,466
Likes: 4,962
I kept getting a message on the dash screen today that my DEF was getting low. First message said I could go around 500 miles. The gauge on the dash said I had just under 1/2 tank and my ForScan gauge said same thing. So right away I figure something isn't right.
I kept getting updates of that message throughout the day, each time saying I had fewer and fewer miles before I would be out of DEF. Meanwhile the gauges were going down slightly but never much past 1/2.
The last notice was that I had 99 miles to go and when I clicked "OK" to clear the message the DEF gauge suddenly dropped to almost empty. Wham - just like that; almost like some float in the DEF tank had been stuck at the half way point but suddenly dropped.
How weird is that? Gauges (both dash and ForScan) say no less than 40% but truck somehow knows the level is getting low. Huh??
And when I filled it, it only took just over 4 gallons and it says it's full. Go figure!
I already had a service appointment for another problem, so I guess I'll have this checked to.
Just wondering if anyone else has seen anything similar.
I kept getting updates of that message throughout the day, each time saying I had fewer and fewer miles before I would be out of DEF. Meanwhile the gauges were going down slightly but never much past 1/2.
The last notice was that I had 99 miles to go and when I clicked "OK" to clear the message the DEF gauge suddenly dropped to almost empty. Wham - just like that; almost like some float in the DEF tank had been stuck at the half way point but suddenly dropped.
How weird is that? Gauges (both dash and ForScan) say no less than 40% but truck somehow knows the level is getting low. Huh??
And when I filled it, it only took just over 4 gallons and it says it's full. Go figure!
I already had a service appointment for another problem, so I guess I'll have this checked to.
Just wondering if anyone else has seen anything similar.
Gauge is working pretty much just like mine does.
And, when you say you "filled" it and was just over 4 gallons, how did you fill it, at the truck stop pump or by jugs?
Because the gauge will show full even when it will hold another 1.5 gallons.
The gauge doesn't use a float like a fuel level gauge, it has sensors that make it drop as the contacts are uncovered, so it does not operate in a linear fashion.
Mountain Pass
Joined: Oct 2021
Posts: 192
Likes: 59
Is this truck new to you?
Gauge is working pretty much just like mine does.
And, when you say you "filled" it and was just over 4 gallons, how did you fill it, at the truck stop pump or by jugs?
Because the gauge will show full even when it will hold another 1.5 gallons.
The gauge doesn't use a float like a fuel level gauge, it has sensors that make it drop as the contacts are uncovered, so it does not operate in a linear fashion.
Gauge is working pretty much just like mine does.
And, when you say you "filled" it and was just over 4 gallons, how did you fill it, at the truck stop pump or by jugs?
Because the gauge will show full even when it will hold another 1.5 gallons.
The gauge doesn't use a float like a fuel level gauge, it has sensors that make it drop as the contacts are uncovered, so it does not operate in a linear fashion.
Thread Starter
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More Turbo
Joined: Aug 2005
Posts: 687
Likes: 215
Is this truck new to you?
Gauge is working pretty much just like mine does.
And, when you say you "filled" it and was just over 4 gallons, how did you fill it, at the truck stop pump or by jugs?
Because the gauge will show full even when it will hold another 1.5 gallons.
The gauge doesn't use a float like a fuel level gauge, it has sensors that make it drop as the contacts are uncovered, so it does not operate in a linear fashion.
Gauge is working pretty much just like mine does.
And, when you say you "filled" it and was just over 4 gallons, how did you fill it, at the truck stop pump or by jugs?
Because the gauge will show full even when it will hold another 1.5 gallons.
The gauge doesn't use a float like a fuel level gauge, it has sensors that make it drop as the contacts are uncovered, so it does not operate in a linear fashion.
I filled it at a truck stop with the DEF pumps out back (truckers lane). I pumped just as I did with '18. It shuts off when full. The gauge went from near empty to completely full (dash gauge and ForScan reads 100%). It might hold a bit more, but it seems the fill should have been more than 4 gallons if it was really empty.
Thanks for the info on the sensors. I'm going to guess something is not right with mine. The whole idea of a gauge reading half but the truck knowing it wasn't is really not right.
I'll follow up at the end of next week after the service call. Thanks for the help so far.
Mountain Pass
Joined: Oct 2021
Posts: 192
Likes: 59
I've never let mine get much below half. I meant works just like mine as it doesn't show every incremental drop in level. It just has sensors at full, half, quarter, very low etc.
Hotshot
Joined: Oct 2015
Posts: 19,698
Likes: 12,825
From: Wyoming
Someone on the forum put forth the theory that if the level in the tank was low it allowed DEF to crystalize on the sensors that are higher up in the tank and that threw off the gauge. I can't say one way or another.
My standard operating procedure is to put in a 2.5 gallon jug just after the gauge shows below 1/2 full. I've had no problems when following that. Where I ran into problems once was when the truck stop I was planning to stop at had their DEF pumps shutdown and I was planning to fill up there. My DEF level dropped down far enough to get the 500 then 50 mile warnings. I added a 2.5 gallon jug sometime between the two warnings but it took quite a few restarts for the system to recognize the new level. I was sweating bullets as I was in the boonies pulling my RV.
It's a goofy system for sure.
My standard operating procedure is to put in a 2.5 gallon jug just after the gauge shows below 1/2 full. I've had no problems when following that. Where I ran into problems once was when the truck stop I was planning to stop at had their DEF pumps shutdown and I was planning to fill up there. My DEF level dropped down far enough to get the 500 then 50 mile warnings. I added a 2.5 gallon jug sometime between the two warnings but it took quite a few restarts for the system to recognize the new level. I was sweating bullets as I was in the boonies pulling my RV.
It's a goofy system for sure.
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Thread Starter
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More Turbo
Joined: Aug 2005
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On my 2018 I would get the 500 mile warning at around 1/4 tank. Then I'd put in 2.5 gallons (Blue DEF) until it was down again. But if I was towing and traveling I would fill it (usually at a truck stop).
Nothing here still explains how at 1/2 tank I would get a 500 mile warning, get repeated warning after than about every 80 miles without the gauge moving, and then get a 99 mile warning and the gauge suddenly drop to less than 1/4.
I went back and look at my receipt when I filled at the truck stop. It was 4.8 gallons. That's close to 5. So maybe it was full at that point and that is why I couldn't get more in with the pump.
Nothing here still explains how at 1/2 tank I would get a 500 mile warning, get repeated warning after than about every 80 miles without the gauge moving, and then get a 99 mile warning and the gauge suddenly drop to less than 1/4.
I went back and look at my receipt when I filled at the truck stop. It was 4.8 gallons. That's close to 5. So maybe it was full at that point and that is why I couldn't get more in with the pump.
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5th Wheeling
Joined: May 2019
Posts: 30
Likes: 4
A couple weeks ago I got the DEF low warning so I topped it off next time I was at a truck stop (400 miles left to go) with 6 gallons put in. However my heart sank when I turned the truck on and the warning was still on and the miles were still counting down (even though the gage showing about 3/4 full). Had to run a few errands so a few starts of the ignition still didn't clear the warning. My truck had never done that before - previously EVERY time I topped off DEF, the warning would clear immediately and the gage would show full. About 5 starts later, the gage JUMPED to full and the warning cleared. Been fine since but I haven't had a need for more DEF yet. I guess I'll try to watch more closely now and refill before the warning comes on.
Hotshot
Joined: Jul 2013
Posts: 14,266
Likes: 2,188
my indicator shows full all the time. every oil change I add a few gallons even though the indicator says full.
I have to be careful as winter approaches....I dont want to full it ...there has to be room for cold weather freezing and expansion.
it would be nice if there was a way to flush this def tank once in a while.
I have to be careful as winter approaches....I dont want to full it ...there has to be room for cold weather freezing and expansion.
it would be nice if there was a way to flush this def tank once in a while.
Mountain Pass
Joined: Sep 2021
Posts: 104
Likes: 56
I have a little over 5K miles on my new F250 and the gauge (Banks gauge and truck gauge) shows 33% still remaining (my gauge acts like my fuel gauge and drops a percentage at a time rather than in big increments). Since I don't put a lot of miles on my truck, a full DEF tank could last me 9 months or more. To keep the DEF "fresh" my plan was to wait until it dropped to around 20% and then just add 2.5 gallons at a time. However, I also worry about the crystalization issue above the liquid level. Has there ever been any evidence that this occurs? It does make some sense that it "could" happen.
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More Turbo
Joined: Aug 2005
Posts: 687
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I have a little over 5K miles on my new F250 and the gauge (Banks gauge and truck gauge) shows 33% still remaining (my gauge acts like my fuel gauge and drops a percentage at a time rather than in big increments). Since I don't put a lot of miles on my truck, a full DEF tank could last me 9 months or more. To keep the DEF "fresh" my plan was to wait until it dropped to around 20% and then just add 2.5 gallons at a time. However, I also worry about the crystalization issue above the liquid level. Has there ever been any evidence that this occurs? It does make some sense that it "could" happen.
Lead Driver
Joined: Nov 2005
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You can flush the tank, pull the hose off and drain it and refill.
As to percentages shown and how the gauge drops during use, I believe the PCM extrapolates the levels based on use estimates rather than exact measurements.
As to percentages shown and how the gauge drops during use, I believe the PCM extrapolates the levels based on use estimates rather than exact measurements.
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More Turbo
Joined: Aug 2005
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The PCM May need to go back to math school. This is a photo I took today. The gauge hasn’t moved in over 400 miles.
