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DEF DTE calculation issue.

1231 Views 3 Replies 4 Participants Last post by  EDank
So I've had my 18 platinum F150 diesel for about 5 months now. I filled it full of DEF when I first got it as the dealer did not and it was about empty according to the gauge, filled it up and took 4-4.5 gallons so gauge was reading correct. I have put on about 3-3500 miles since owning it doing some towing with it. My DEF level according to the gauge was showing between 1/4 and 1/2 and then I got a warning saying my def level was low and I had 400 miles to refill as I had just left on a fishing trip pulling my enclosed trailer 230 miles one way. I brought with a 2.5 gallon jug of DEF just in case but figured the dte calculation would change along the way, it did not. On the way home I got a message saying the def tank was empty and I had 100 miles to go until the speed would be limited to 50mph. My def gauge still showed above 1/4 tank, but the next town I pulled over and poured my 2.5 gallon jug in and truck was happy instantly. Def level jumped to 3/4 full and now the dte calculation was up to like 6000 miles. So the gauge was working correctly but I am wondering why it was telling me the tank was empty when it clearly was not. Anyone have any experience with def level and dte calculation being off?
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I can’t speculate why this happened but I do know that I don’t let mine get below 1/2. I was in NMex on a trip and was driving on a rough side road with my DEF sitting at just under 1/4. Got an error code and slipped into limp mode. The truck was new so I took it to a local dealer on a Sat. The place was a zoo and wouldn’t be able to get to it til Monday. But, he asked if he could read the code. It was a DEF squirt error, missed one I guess. The he asked me if I wanted to erase the code. Uhhhhhh, YES!. Filled up the DEF and the code never came back. The rough road must’ve caused the DEF to slosh and miss a cycle. IMO, the whole DEF and EGR setup is made to fail. It’d be nice if we could do like the Canadians and delete this stuff forever. Isn’t it a huge penalty to be towing something and your truck is going to limit you to 50mph because of the DEF? On a major highway that’s a real safety concern.
I guess I'm in the minority but based on my experience original-owner Volkswagen and the Oasis report on my previously-owned F-150, I am at 180,000 combined miles without a single DEF-related hiccup. I don't do anything special; fill it up when I have 1000 miles of range left and store the DEF in the basement to extend its life.

I live in a near-Arctic climate, which is a harsh environment. To function properly, the tank heater has to thaw the DEF to at least -11 def F. After shutting down, the system also has to purge any DEF that remains in the pump/line/injector so that doesn't freeze. In addition, DEF can crystallize, plugging the injector or causing the level sender to get stuck in one position. Working it its favor is the low NOx generated b a cold engine, giving the heater time to catch up. It's a pretty impressive system that is similar to the ammonia injection systems used on many industrial power boilers. Like almost any system, if it is not carefully engineered, it will come back to bite you.

I twitch a bit at the thought of a malfunction code triggering a reduction in engine output or a programmed no-start, but what bothers me more are ignored check engine lights. My work has me riding in probably 100 airport shuttles and taxis every year. The engineer-in-me always looks at the odometer and the instrument panel in general. I am being conservative in saying that 90% of these vehicles have CELs. As long as the engine runs, the driver/owner does not care. Frankly, I wish more cars had automatic limp modes for generic CELs.
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Towing the last few weeks my DEF gauge was very strange. Was at 1/2 full when I went to top it off it would only take 2 gal and one quart. Halfway to Fla from Nj I get the DEF low 500 miles to limp mode. Just before I got the message the gauge was showing 1/2 full. I top put in a 2 1/2 gal jug and the gauge only comes up to 3/4 full. I used over 8 gal of DEF for my 3600 mile trip. Seems a bit excessive compared to the 2013 RAM I replaced with this F150.
All in all I’m very happy with this truck. It’s towing ability really surprised me.
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