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I have been using DEF from Walmart lately and it had been 4-5 weeks since I had filled it up. Taking the message to heart, I added more DEF to dilute what was in the tank. I'm guessing it only took 2-3 quarts to fill. That didn't fix the issue within the first step of mileage countdown to 55 mph. I was going to drain the tank and totally refill it with 2 fresh jugs of DEF . . ..
In the future I'd suggest running the DEF down to maybe 10-15 percent and then only put in one jug. Unless you're putting a ton of miles on that amount of DEF will last quite a while, and the average age of DEF in your tank will be less on average.
 

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Discussion Starter · #83 ·
Hmmm....does this suggest that the limp countdown could be stopped by simply unplugging the NOx sensor? Or would that just trigger another dreadful situation?
I doubt it. Other calculations depend on the readings coming from the NOX sensor, so if it's not there, these calculations will yield results that would likely trigger the countdown.

For the other nerds in the house: Something I noticed when poking around the stock file parameters in EFILive (seriously just looking to understand better - nothing illegal) is that the DTCs have tags for DTC Type, and DTC MIL:
  • DTC Type
    • X: Not Reported
    • A: 1 Trip, Emissions Related
    • B: 2 Trips, Emissions Related
    • C: Non Emissions.
  • DTC MIL
    • MIL
    • No MIL
My hunch is that these bits, or some combination thereof, get used to trigger the limp mode countdown. My hypothesis so far: anything with DTC Type A or B ("Emissions related") will trigger limp countdown, and the operating system prevents any DTC with these Types from being ignored or simply cleared to indefinitely reset the clock.
 

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Not knowing where the heaters are in the DEF tank, my thinking was and is that keeping it 2/3 or better full would be a good thing. We do get below the DEF freezing point (12 deg F) up here in Vermont. I had a friend who had a Ford F350 that the DEF tank froze up and busted (very expensive he said).
 

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Not knowing where the heaters are in the DEF tank, my thinking was and is that keeping it 2/3 or better full would be a good thing. We do get below the DEF freezing point (12 deg F) up here in Vermont. I had a friend who had a Ford F350 that the DEF tank froze up and busted (very expensive he said).
I suppose that might justify filling it full around November.
 

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Filling the DEF tank full can lead to "crusty cap syndrome". I find that following an adding a 2.5 gallon jug at 30% screen routine has stopped the stuck cap issue. It does not hurt to twist the DEF cap while fueling up to keep it free either, just don't stick the fuel hose in there :)

Fortunately my truck doesn't often see super cold temps as it is garaged.
 
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Filling the DEF tank full can lead to "crusty cap syndrome". I find that following an adding a 2.5 gallon jug at 30% screen routine has stopped the stuck cap issue.
Not on my truck! I've never added more than 2.5 gallons and 30% is probably as full as it's ever been before I have added DEF. Still get crusty cap somehow.
 

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Not on my truck! I've never added more than 2.5 gallons and 30% is probably as full as it's ever been before I have added DEF. Still get crusty cap somehow.
Oh, that darn crusty cap :LOL:

I did spray my cap with a tiny bit of silicone lube, that might have helped too. Was really worried for a bit there that I might strip out it's internal plastic teeth, as I had to use a vice grips to get it off one time.
 

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Oh, that darn crusty cap :LOL:

I did spray my cap with a tiny bit of silicone lube, that might have helped too. Was really worried for a bit there that I might strip out it's internal plastic teeth, as I had to use a vice grips to get it off one time.
I think the opening every tank of fuel really helps.

BTW, I was able to snag a warranty replacement of my cap after the incident where the dealer couldn't remove it. They just gave me the cap without requiring another trip to the service department. The concern was it might have been weakened due to the force required to remove.
 

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Interesting. GM does sell a lot of relatively emissions uncorked 2.8s in Brazil.

Love how these trucks smoke their EPA numbers. Admittedly tuned and do quite a bit of highway driving, but my '17 is averaging 27.7 MPG over the last 46K miles per the DIC. Even with a slightly optimistic DIC, it is probably doing 26.5 to 27. Used to hand calculate and found the DIC was not that far off.
 
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I'd take that window sticker with a grain of salt, they are notoriously inaccurate for model years just coming out. GM still lists the only assembly location as Thailand.


Sent from my SM-G986U using Tapatalk
 

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I'd take that window sticker with a grain of salt, they are notoriously inaccurate for model years just coming out.
I thought it was wrong due to having too low of fuel mileage, but then I looked at my LT's sticker and they were the same. Amazing out much the EPA understates fuel mileage on diesels.

But maybe after GM entered into a contract to sell the Thailand plant they quietly in the middle of the night moved all the equipment to Brazil. ;)
 
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