DEF Gauge Inaccurate

[Mike Wenrich]

Since owning my 2014 I have always added DEF when the gauge showed 1/2 and it always took 2 1/2 gallons no problem. Couple weeks ago and after sitting much of the winter I wanted to run the DEF down as much as I dared to get the old stuff out. So the wife and I went on a 200 mile drive with my gauge showing a hair below 1/2. For some reason, I threw a box of the stuff in the back. Got over onto the 5 FWy heading toward Stockton when all of a sudden I got a check engine code and a message saying something to the effect that DEF was not being detected and to go the dealer. Kept throwing the code and dinging about every minute. Annoying !!!! I finally found an off ramp and added the box I had in the back. Reset the code and drove another 100 miles returning home, with the gauge showing full.

Got to thinking...I wonder how much more I could have added? Bought another box and was able to add two gallons. So the gauge was/is waaaaay off. Those that fill at the truck stops and use the bulk hose probably know how accurate their gauge is but I don't have one of those near me. Since I am sheltering in place and maybe you are too, I thought someone else might want to know. Yes I'm bored.

 

[sag2]

Mike, it would be helpful to know what code(s) you had before you cleared them.

 

[MtnRider]

Yeah the gauge is not linear, all of them are like that. Probably just a random glitch if it cleared. I had the same thing happen last year, added more DEF, cleared the fault and it never came back. I wouldn't worry too much about it unless it pops up again

 

[AH64ID]

The owners manual even talks about how inaccurate the gauge is and may not move for 2 gallons of use.

I fill at the pump and it’s fairly consistent so far, but I’ve only filled it a handful of times in 13K miles.

 

[BarryG]

There is a video on YouTube about the inaccuracy of the readout. Iirc it still shows as full well past a gallon of use. That with a 5 gal tank 20 + percent used before it even starts showing a decline on the gauge

 

[Wiredawg]

My 2017 Ram 5500 holds 9 gallons... at the half mark, it takes 2.5 gallons to bring it to full. Mine sat for several months while is was recuperating from surgery. I haven't had any codes. Drive it every week or two now to keep er running.

Cheers, Ron

 

[Mike Wenrich]

Sag....I do wish I had written the code down before clearing. At the time I was more concerned about getting home without being on the "hook". But I do recall it was something very different. If this makes any sense, it might have been a Q code with numbers. Without my readers on the Q might have been a P though. I'm certain the code was thrown because I was out of DEF even though the gauge was showing nearly half and that is the reason I posted this issue. At this point I don't believe it was any other issue. And probably if I had one of the better code readers I could call the code back up.

 

[Fmilford]

My 2017 gets around 5k before I need to refill the DEF. About 6 months ago I noticed that my gage is stuck on full. I have ran 5k and the gage is still showing full. I have been told that once you get down to less than a 1/4 tank of DEF that your engine will not let you go over 35mph. What sensor sets that off? If it is the gage, then I can run forever and not need it anymore.

 

[sag2]

My 2017 gets around 5k before I need to refill the DEF. About 6 months ago I noticed that my gage is stuck on full. I have ran 5k and the gage is still showing full. I have been told that once you get down to less than a 1/4 tank of DEF that your engine will not let you go over 35mph. What sensor sets that off? If it is the gage, then I can run forever and not need it anymore.

Nice try, but not exactly correct. Technically you could run forever with the gauge stuck on full, but the NOx sensors would set a CEL and eventual derate once the NOx conversion did not meet the requirements. Consider yourself lucky that it is stuck on full and not empty, especially out of warranty. The new tank/sender is around $2,000 to replace. When they are stuck on empty it will also go into a derate eventually.

 

[Fmilford]

$2000 WTH? The truck only has 52k miles on it. I guess I will just keep track and keep it filled every 4k miles. It was weird, this happened right after I used a pump to fill it up instead of the blue bottles.

 

[AH64ID]

$2000 WTH? The truck only has 52k miles on it. I guess I will just keep track and keep it filled every 4k miles. It was weird, this happened right after I used a pump to fill it up instead of the blue bottles.

Maybe it's fuller than you think... thou the best I have gotten is 1K miles per gallon on DEF.

I have only filled with a jug once, the rest has been pump fillups.

 

[bcbender]

I filled my DEF tank for the first time and it took 5gal.. This was after the light came on, then about 100mi dn the road it said "200mi left to 5mph limit". Like many I plan to fill at the truck stops and only carry a box in the 5er for just in case situations, ( I used Loves on I85). After I got home and cleaned the little bit that leaked onto the filler door and was white and chalky, I saw a decal on the filler door saying "I believe" not to fill it completely??.. I cannot find anything in the OM about it, is it OK to fill it to FULL? I let it pump until the pump clicked and called it "good". Logged the Miles and was going to track the usage using the same method as the main fuel tank. Just asking since I have never had a DEF system yet, and don't need any problems.. My 20' has a DEF gauge, it took it a few min to come up to full; and was much slower than the diesel gauge response, but seems to be working as I'm at 7/8 tank now.

 

[R.Taylor]

Don't overfill the DEF otherwise the computer will FTHO and tell you to see service and it will do the limp mode count down due to an erratic DEF tank level sensor code. Draining the excess out is a PITA as there is no drain on the tank. I always top off at the half tank mark... Almost one box. Sometimes it takes a bit for the gauge to show 100% after filling it... I figure there's so much crystalized urea on the innards that it's taking a little time to dissolve.

 

[bcbender]

So how do you really know if its "overfilled" You cant count on the gauge as it is slow to respond and from what Ive read can be more of a "general" idea of fill, it is demarked in %fill not actual fill. I assumed that FCA would've out an airspace in the tank so that the pump would stop prior to overfilling (same as a fuel tank and I know what happens when you ASSUME)? That's why I was asking as I can see potentially overfilling via gravity with the box vs. pressure filling with the DEF pump and utilizing the expansion area designed into the tank (hopefully).

 

[DonFitzwater]

Don't overfill the DEF otherwise the computer will FTHO and tell you to see service and it will do the limp mode count down due to an erratic DEF tank level sensor code. Draining the excess out is a PITA as there is no drain on the tank. I always top off at the half tank mark... Almost one box. Sometimes it takes a bit for the gauge to show 100% after filling it... I figure there's so much crystalized urea on the innards that it's taking a little time to dissolve.

I disagree. Overfilling won't hurt anything or cause any abnormalities. If it does, something is wrong with your truck. The only real problem with filling to the top is in cold weather as the filler neck can freeze solid and won't thaw out while the tank does and then you can't add more!

 

[Ltngdrvr]

Don't overfill the DEF otherwise the computer will FTHO and tell you to see service and it will do the limp mode count down due to an erratic DEF tank level sensor code. Draining the excess out is a PITA as there is no drain on the tank. I always top off at the half tank mark... Almost one box. Sometimes it takes a bit for the gauge to show 100% after filling it... I figure there's so much crystalized urea on the innards that it's taking a little time to dissolve.

I disagree. Overfilling won't hurt anything or cause any abnormalities. If it does, something is wrong with your truck. The only real problem with filling to the top is in cold weather as the filler neck can freeze solid and won't thaw out while the tank does and then you can't add more!

Yeah, definitely not true, I fill mine all the way to the top of the filler neck every time I fill at the truck stop pump, never any issue and the ecm never throws a code or sets a warning message.
The only possible issue that you might face by completely filling to the top of the filler neck is if you then don't drive it and the temp falls below the freeze point of DEF, 10 degrees F or -11 degrees C, and the DEF freezes up, it will then split the filler tube because of the expansion. This is not an issue for the tank, it is designed with frozen DEF in mind, but the filler tube isn't made to take the expansion.

 

[DonFitzwater]

it will then split the filler tube because of the expansion. This is not an issue for the tank, it is designed with frozen DEF in mind, but the filler tube isn't made to take the expansion.

It won't hurt the filler neck either, I have 7 years of winters and have been filling to the top regularly.

 

[Ltngdrvr]

It won't hurt the filler neck either, I have 7 years of winters and have been filling to the top regularly.

With DEF frozen in the filler neck???
If so, you've been lucky.

 

[R.Taylor]

Well... My 19' threw a code and went to countdown cause I overfilled it... Guess Y'all are lucky.

https://www.turbodieselregister.com/threads/code-p203e-service-def-system-message.269553/

P203E - Reductant (DEF) Level Sensor Circuit Intermittent/Erratic

 

[R.Taylor]

So how do you really know if its "overfilled" You cant count on the gauge as it is slow to respond and from what Ive read can be more of a "general" idea of fill, it is demarked in %fill not actual fill. I assumed that FCA would've out an airspace in the tank so that the pump would stop prior to overfilling (same as a fuel tank and I know what happens when you ASSUME)? That's why I was asking as I can see potentially overfilling via gravity with the box vs. pressure filling with the DEF pump and utilizing the expansion area designed into the tank (hopefully).

Overfilled is when no more bubbles come out of the filler and it's DEF all the way to the top.