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Apparently it's not expected by some readers that the gen2 diesel may provide no DEF warnings until there are just 300 miles to go. Another owner here indicated surprise, and I too expected way more than 300 miles warning.

Top off the DEF before you roadtrip!
Otherwise the car might decide that the first DEF warning (with 300-miles-to-go) and your enthusiastic first tentative clumsy DEF refill will be mandated to occur when you are in the middle of subzero windy blizzard conditions at a service area on I-90 near Erie & Buffalo.
 

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I would think the real lesson learned here is to know how to top off the DEF before you go on any road trip or expect bad weather.
 

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When fuel stops are more than 300 miles apart, yes.

But I thought it would say "35% full" before it would say "300 miles remaining".
The DEF tank does not need to be filled as often a the fuel tank. It is not like fuel will go 700 miles but DEF only 300. The opposite is the case.
 

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Mine always tells me the percentage that is left, usually around 37%. Other than that it's says full. I bought the VW AdBlue off Amazon to get the cool unspillable bottle. It's only half gallon, so it would need to be refilled 4 times to get the 2.5 gallons in that the 37% indicates. Lot better than spilling it all over the side of your car lugging the 2.5 gallons jug around by that tiny hose.
 

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The DEF tank does not need to be filled as often a the fuel tank. It is not like fuel will go 700 miles but DEF only 300. The opposite is the case.
Right.
So there's no reason not to tell the driver 'I need DEF in 1000 miles', so that the driver can include it in his next fuel stop.
 

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Right.
So there's no reason not to tell the driver 'I need DEF in 1000 miles', so that the driver can include it in his next fuel stop.
Is DEF usage linear with respect to miles driven, or is it based on engine speeds and miles driven?
 

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Is DEF usage linear with respect to miles driven, or is it based on engine speeds and miles driven?
People generally say it's proportional to fuel use.. but knowing the kind of engine parameters that would require it, think excess air in the combustion process, with high pressure and temperature... That is what makes NOx, and DEF is injected into the exhaust to react in the SCR catalyst to scrub NOx from making it out the tail pipe.. so, think of conditions where those parameters might be met.. ironically lower engine loads, higher RPM etc.. so it's a bit more complicated to determine all the parameters that determine actual DEF consumption.

Sent from my Moto G (4) using Tapatalk
 

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Right.
So there's no reason not to tell the driver 'I need DEF in 1000 miles', so that the driver can include it in his next fuel stop.
Really? You need the car to tell you that? Just fill it every time you get fuel if that is the case. 300 miles of warning/driving range seems plenty - even in the Mohave Desert.

In fact, 1000 mile seems excessive to the point of being ignored - causing people to run out.
 

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John, you're not getting my point.
I'm saying if it's going to warn you, it should give warning in ample time so that you can take care of it without making a special stop just for the DEF. It should be programmed for driver convenience, not just to make the driver satisfy the car's needs.

Since the logical way of dealing with the DEF is to include it in your next fuel stop, 300 miles isn't long enough if you don't plan on buying fuel in the next 300 miles. I don't want to be rushing home on December 26th and get a warning "fill DEF within 300 miles" when I'm 400 miles from home, had my final fuel and meal stop half an hour ago and have to drive to work tomorrow morning. That's just stupid software making my life more difficult.
 

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John, you're not getting my point.
I'm saying if it's going to warn you, it should give warning in ample time so that you can take care of it without making a special stop just for the DEF. It should be programmed for driver convenience, not just to make the driver satisfy the car's needs.

Since the logical way of dealing with the DEF is to include it in your next fuel stop, 300 miles isn't long enough if you don't plan on buying fuel in the next 300 miles. I don't want to be rushing home on December 26th and get a warning "fill DEF within 300 miles" when I'm 400 miles from home, had my final fuel and meal stop half an hour ago and have to drive to work tomorrow morning. That's just stupid software making my life more difficult.
I understand. What I would prefer is a separate DEF "fuel gauge" with a warning light similar to what is used in a Class 8 truck.

Alternatively, just fill it every time. I think that "too much" warning is also problematic is my point. My ex wife had a car that had a "low fuel light" at 8 gallons (20 gallon tank). She got to the point that she just ignored the light. Three times she ran it out of gas!

Programing to taste would certainly work for me also.
 

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Ideally, I'd notice when it went from 100% to 37%, and plan to make my next fueling at a truck stop with DEF pumps. But I'd appreciate it if it would pop up on the display when it dropped below "full". Then I'd push the OK button to dismiss it, and try to remember to pump some DEF next week.

Actually, in an ideal world, it would read 50% at half full instead of reading full, but that's another case where they put protecting the car from idiots ahead of making it convenient for knowledgeable drivers...
 

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People generally say it's proportional to fuel use.. but knowing the kind of engine parameters that would require it, think excess air in the combustion process, with high pressure and temperature... That is what makes NOx, and DEF is injected into the exhaust to react in the SCR catalyst to scrub NOx from making it out the tail pipe.. so, think of conditions where those parameters might be met.. ironically lower engine loads, higher RPM etc.. so it's a bit more complicated to determine all the parameters that determine actual DEF consumption.

Sent from my Moto G (4) using Tapatalk
So DEF consumption is not limited solely to the regen cycle?

This is my first DEF vehicle so I’m still learning. I always assumed regen was only time DEF is consumed.
 

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So DEF consumption is not limited solely to the regen cycle?

This is my first DEF vehicle so I’m still learning. I always assumed regen was only time DEF is consumed.
No, from my research it is injected to react with the SCR catalyst and the reaction reduces NOx (though I don't think at all times, hence the NOx sensor before the SCR). The non-DEF LNT method (on my 2009 Cummins Bluetec) uses an absorption method (Lean NOx Trap). When that "trap" has absorbed all the NOx it can.. the Regen for the LNT (different from DPF regen) burns off the NOx using fuel in the exhaust stream. Since SCR uses no fuel for regen of the SCR, and uses small amounts of DEF.. the SCR technology has won the competition since it yields better MPG, and with less engine oil fuel dilution problems associated with post injection for the Regen events, now no diesels use the LNT emissions system.

https://www.dieselforum.org/about-clean-diesel/what-is-scr

Also, the 2012 Jetta I had was LNT emissions.. and the "cheat" was a big contributor to the better MPG than it would otherwise not get with the proper LNT regens taking place.
 
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No, from my research it is injected to react with the SCR catalyst and the reaction reduces NOx (though I don't think at all times, hence the NOx sensor before the SCR). The non-DEF LNT method (on my 2009 Cummins Bluetec) uses an absorption method (Lean NOx Trap). When that "trap" has absorbed all the NOx it can.. the Regen for the LNT (different from DPF regen) burns off the NOx using fuel in the exhaust stream. Since SCR uses no fuel for regen of the SCR, and uses small amounts of DEF.. the SCR technology has won the competition since it yields better MPG, and with less engine oil fuel dilution problems associated with post injection for the Regen events, no no diesels use the LNT emissions system.

https://www.dieselforum.org/about-clean-diesel/what-is-scr

Also, the 2012 Jetta I had was LNT emissions.. and the "cheat" was a big contributor to the better MPG than it would otherwise not get with the proper LNT regens taking place.
So if I’m understanding this correctly, the SCR ‘cleaning’ process uses DEF and the DPF Regen uses diesel fuel. Both processes occur independently of each other.

Correct??

This is my 3rd diesel but never had all this emissions stuff to deal with.

The 09 TDI required no DEF and the 06 Cummins 5.9 (2nd owner) was modified before I bought it so it never had any emissions stuff on it, no Cat, just a Magnaflow muffler and 4” exhaust (no emissions testing in my part of the state).

Never had a CEL in either vehicle with over 400,000 miles combined.
 
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