Unusual DEF Behavior

TMac99 · August 28, 2017

I now have 6,000 miles on my 2017 Duramax. Twice now I have had the 30% DEF caution come on and at the same time have had DEF mileage remaining warnings showing only 130 miles and 160 miles. On both occasions, the DEF level went from 30% to reading "Low" after about 50 miles, along with the caution that says something like "DEF Low - engine will soon be speed limited". In my 2015 Duramax, 30% DEF corresponded to approx 1000 miles remaining, now it seems to correspond to about 150 miles remaining. Also, assuming that the DEF tank was full when I got the truck and again full after a service where they said they topped up the DEF tank, both times I got the 30% DEF light after about 1000 miles of towing a 7500 lb travel trailer. I have now used 4 tanks of DEF in 6,000 miles (most of those miles towing the 7500lb travel trailer)

Is this normal? Anyone else seeing this behavior?

P.S. The first time this happened, I had to find DEF in the middle of nowhere, Montana, and filled up with some unknown brand of DEF. Shortly after I got a CEL The code was P0821). This happened again 3000 miles later. The fix, applied after the second incident) according to Chevy dealer was to reprogram the TCM and ECM.

2017HD · August 29, 2017

I went through 5 +gals of DEF (assuming the dealer filled it to start with) in about 3800mi with about 500mi of towing and a couple of road trips but mostly around town driving. I was towing when I got the 1000mi warning. I dismissed it and noted the mileage - thinking I had some time. I put another 100 mi or so on a road trip without the TT and then when towing the TT home (about 150 mi) I got two more mileage warnings. I did not get to the speed/power reduction warning. I added a full 5 gal of DEF and all the warnings went away and the "gauge" says OK.

I know that your DEF usage is related to your MPG - the higher the MPG the less DEF is used - therefore my towing and around town usage would probably go through more DEF than flying down the road empty.

I would love a real DEF gauge

Colossus · August 30, 2017

Just used up 4 gallons of DEF in my 2012 in about 3000 miles. Sometimes it's 5000 miles, sometimes it's less. Just the way it goes with the diesel. no logic to it, get used to it I suppose.