# Def percentage going down



## Sloverado (Aug 14, 2019)

I top off def every other week as I check car over. The percentage keeps going down and now I’m about 18% and won’t be home for 3 more days. I’ve unhooked battery for a couple hrs and still didn’t change anything. The tank is full with a fresh jug so I know it’s not low. It sits in a heated garage so frozen isn’t it I don’t think. Anything I can do?


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## MRO1791 (Sep 2, 2016)

Sloverado said:


> I top off def every other week as I check car over. The percentage keeps going down and now I’m about 18% and won’t be home for 3 more days. I’ve unhooked battery for a couple hrs and still didn’t change anything. The tank is full with a fresh jug so I know it’s not low. It sits in a heated garage so frozen isn’t it I don’t think. Anything I can do?


Sounds like you need a DEF level reset. Also, it's a bad idea to frequently top off DEF. The system calculates level and only has a couple of actual level sensors. It's probably thinking your full sensor is stuck and forcing a lower level by calculation.


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## oregon_rider (Jul 21, 2017)

Manual states you are to add at least two gallons if engine power reduced.. my daughter ran into this issue on trip to California. She only added a gallon and nothing changed with reduced power etc.... It didn't seem to recognize new level unless you add at least two gallons.

Def goes bad quickly so you are not supposed to keep it topped off as you are....

Let it get down to where you get a notification or warning. Then top off adding more.than 2 gallons.

You may need to go to dealer to have reset on level in order to not get reduced power.even though your tank has plenty of fluid. Me, I would do this as a precaution....

And going forward only fill when def tank will take at least a 2.5 gallon jug of def...

With a 3.8 gallon capacity, refilling when it hits 20 percent will allow.you to safely refill using 2.5 gallon jug of def without risk of overflow.

Jeff


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## Snipesy (Dec 7, 2015)

Honestly it should be fine. As long as there is DEF in the reservoir next to the heating element it should not give any warning message, even if it says 1%.


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## MRO1791 (Sep 2, 2016)

Also, if you get the Torque Pro app, have an android device, OBD 2 bluetooth adapter and BiScan for GM, you could do your own DEF level reset without the dealership. I can do my own with this set up. The BiScan for GM is an amazing add-in for Torque Pro for these cars


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## MRO1791 (Sep 2, 2016)

Snipesy said:


> Honestly it should be fine. As long as there is DEF in the reservoir next to the heating element it should not give any warning message, even if it says 1%.


Will it reset on it's own at some point? My Gen 1 was not resetting, so I did a DEF level reset with your app, that got it back to 100%, now ironically it never lowers, so I just check and top off by dipstick!


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## Snipesy (Dec 7, 2015)

MRO1791 said:


> Will it reset on it's own at some point? My Gen 1 was not resetting, so I did a DEF level reset with your app, that got it back to 100%, now ironically it never lowers, so I just check and top off by dipstick!


Over a long time.
I don’t know if the def level reset works on the gen 2s because GM disabled it unless you’re in programming mode. Which is as silly as it sounds.


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## Barry Allen (Apr 18, 2018)

Sloverado said:


> I top off def every other week as I check car over.


Why? Run it down to near empty (when it starts giving you warning messages) and then refill.


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## Sloverado (Aug 14, 2019)

Ok guys I’ll pry swing into the dealer if it doesn’t do something here soon. When I say top it off it means when the warning say 980 miles tell empty. There is times I will travel 2500 miles in a couple weeks time frame


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## DavGr (Dec 12, 2019)

Topping off the DEF isn’t the best idea, I add whenever it gets to just below 20% & add the full 2.5 gal jug. When you have partial jugs of DEF you can have urea crystals form in the jug due to exposure to air which will plug the dosing injector. 

Seen it happen on our larger trucks at work. Once the urea crystalizes on the walls of the jug it won’t go back into solution. Takes warming up the deionized water and agitation to put the urea backs into suspension.


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## Sloverado (Aug 14, 2019)

Ok had dealer reset def sensor and it reads 20% and I know it is full. Hope it climes up after while


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## Sloverado (Aug 14, 2019)

Nope didn’t work went to empty. Reset it again and only went to 20% again. We are going to try it again without filling to run it down. May have to setup a time for them to look into it further. Everything checks out fine when hooked up to computer. They have no idea.


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## Snipesy (Dec 7, 2015)

Sloverado said:


> Ok had dealer reset def sensor and it reads 20% and I know it is full. Hope it climes up after while


I don’t think you can reset the def level on the gen 2s. Yes your dealer has the option to do it, but it doesn’t work because GM.

The only thing you can do is replace the def heater really.


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## phil1734 (Aug 30, 2019)

I had to replace my def heater/level sensor at about 7,000 miles. It was pretty much bad from the factory, along with the EGR cooler. 

However, I had a check engine light on for "service after treatment system" or something to that extent. Maybe you only get the warning if the heater is out? Even if the part is still bad?


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