# Def usage and the lies the dealer tells you.



## boraz (Aug 29, 2013)

4000km of city or hwy?

not that it really matters, but if it were mostly hwy, then yeah thats waaaaaay too much

they dont want to do warranty work, they get paid less than if it was out of warranty


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## Bohner (Nov 3, 2020)

95% highway. I drive 200km a day highway 100kph 2 lane/110kph on 4 lane. I set my cruise at 40kph and increase my speed with the cruise control to 110 and leave it there. I don't drive it hard so I don't believe that it should be using that much def.


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## MRO1791 (Sep 2, 2016)

Bohner said:


> Hi I have a 2017 cruze gen 2 diesel. In Saskatchewan I am using around a full tank of def in 4000km/2500 miles. I believe this is being used excessively. I have talked to my dealer and they gave me some bull excuse that they believe that is reasonable. So I asked him what the nox values are from the sensors. This was their response
> "There are no way of reading them nor a reason to try. They are like O2 sensors. They will register if there is a failure in the DEF fluid readings. Right now everything is working as it should."
> I believe he is wrong because I've seen guys on here with the torque app showing nox levels. Am I wrong? My belief is that the nox sensors are faulty but how would I prove that without having to buy them.
> 
> Thanks for any response.


Yes, that seems excessive. I go more than double that in mixed driving on my 3 Gen 2 Diesels, at the typical oil change interval it's still about 40-50% DEF remaining. I would check for leaks.. also if you are using that much I have to wonder if it's doing anything strange to the SCR catalyst. 

Getting warranty work at any dealership is a chore these days, they rely on the onboard diagnostics to throw a code before they will do anything, but I would think at some point with that kind of usage there should be some kind of code, the system monitors the tank level, and pump rate, if there is a mismatch it seems it should trigger some kind of diagnostic trouble code, but these things can be delayed to prevent false alarms.


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## Ma v e n (Oct 8, 2018)

It's because there's no way to tell if the vehicle is using too much just monitoring NOx ppm readings, just like you can't tell fuel economy by watching HO2S voltage output.

Additionally there's no set available consumption spec, so essentially if the vehicle isn't setting a P249E, (or another aftertreatment specific DTC)DEF consumption isn't considered too high and a warrantable condition. There aren't any TSBs or other documents related to excessive DEF consumption.

Typically DEF consumption aims to be near 2-3% fuel consumption. I've seen 6-7% in healthy vehicles as well.
Unhealthy vehicles are usually double digits if they are leaking or something


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## BodhiBenz1987 (Jan 13, 2018)

It doesn't matter how wrong something is, unless it's across a black and white line that triggers a CEL, they won't touch it. Case in point my car does active regenerations every 150 or so miles of 90% highway and that's "normal" even though others who drive similar patterns go 700-800 miles between. So to be honest, I doubt you will win any battles showing them specific values. I wouldn't even blame the dealer, mine even agreed something was wrong with my car but was given a red light when they tried to get help from GM Tech. Basically most things have to hit the threshold where a CEL comes on to be considered bad enough to fix or investigate. Which kind of sucks if you have a car that has a glitch that isn't apocalyptically bad, but is a significant nuisance and potentially causing premature damage.
For what it's worth, looking at my last DEF fill, mine consumed 2.5 gallons in 4,500 miles, during which it consumed about 83 gallons of fuel. So around 3% DEF to fuel. DEF consumption is higher during a regen as far as I understand so I imagine a normal car would be lower than mine. So compared to that and what others say, yours does seem high. Is it always that way? Is it a new development? I'm no mechanic but maybe there's a fuel quality issue that's causing more NOx and thus more DEF usage.


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## Barry Allen (Apr 18, 2018)

BodhiBenz1987 said:


> DEF consumption is higher during a regen as far as I understand


During regen I believe the EGR is entirely disabled. For a regen cycle you want exhaust temperatures to be very high so you can combust the soot trapped in the DPF. This is accomplished by turning off EGR (higher combustion temperatures in the cylinders) and then adding excess fuel injected during the exhaust stroke where it combusts in the exhaust stream to really roast that DPF at high temperatures.

I don't know about DEF consumption during regen. It stands to reason that the lack of EGR results in higher NOx generated, and maybe some excess DEF is injected to try to clean up that exhaust stream a bit. 

Then again, the EPA exempts emissions of vehicles during certain engine operating parameters that are infrequent and not a substantial amount of the time that the engine operates. Basically, the EPA knows that engines cannot achieve 100% emissions compliance and they exempt regen cycles because it's every once in a while, hard to control emissions during the cycle, and it's not a major amount of the time that the engine spends operating. If this is true, the ECU could theoretically disable DEF injection because it's a quick 5-minute period of engine operation where emissions aren't controlled due to the EPA exemption.


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## Bohner (Nov 3, 2020)

It has always been high but is slowly getting worse. Usually was 5-6000km/tank nowhere near others 10000km/tank. My understanding is that def is injected as needed vs the pre and post nox sensors. That's why I think it is a problem with the sensors. Could dye in the fuel also be a Culprit? I wouldn't think as much but you never know.
The first time I asked them about the def usage they told me the dpf is regenning in its proper interval which blew me away that that really has no bearing on def too much. I understand that if it's not throwing a code then **** me they won't do anything. I have an equinox diesel and I believe the nox sensors are the same. I was thinking of switching them to see if it would change the def consumption as well.


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## TDCruze (Sep 26, 2014)

Bohner said:


> Hi I have a 2017 cruze gen 2 diesel. In Saskatchewan I am using around a full tank of def in 4000km/2500 miles. I believe this is being used excessively. I have talked to my dealer and they gave me some bull excuse that they believe that is reasonable. So I asked him what the nox values are from the sensors. This was their response
> "There are no way of reading them nor a reason to try. They are like O2 sensors. They will register if there is a failure in the DEF fluid readings. Right now everything is working as it should."
> I believe he is wrong because I've seen guys on here with the torque app showing nox levels. Am I wrong? My belief is that the nox sensors are faulty but how would I prove that without having to buy them.
> 
> Thanks for any response.


Mine in Saskatchewan uses about the same amount. It is around the norm from what I have seen. 4-5000km on a 9.46L jug is about where I am at, although I do not track my useage that close.


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## Bohner (Nov 3, 2020)

I just do a trip 2 reset on fill. The dealer also tried telling me that there def is better and that's why is using more. A jug of def at the dealer is 24$. A fill is 8$ @Petro. How could you even justify 24$ a jug.


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## TDCruze (Sep 26, 2014)

Bohner said:


> I just do a trip 2 reset on fill. The dealer also tried telling me that there def is better and that's why is using more. A jug of def at the dealer is 24$. A fill is 8$ @Petro. How could you even justify 24$ a jug.


Thats is a load of BS. All DEF is the same and even if it was "better" it should use less. 

I wonder if a leaky injector could be an issue? 
It would be wasteful but likely stll appease all sensors.


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## Bohner (Nov 3, 2020)

I can't find any leaks to the system at all.


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## TDCruze (Sep 26, 2014)

Bohner said:


> I can't find any leaks to the system at all.


I would guess leaking into the exhaust, maybe stuck open a bit? Just a guess. Would still take care of nox but be wasting def.


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## BodhiBenz1987 (Jan 13, 2018)

Barry Allen said:


> During regen I believe the EGR is entirely disabled. For a regen cycle you want exhaust temperatures to be very high so you can combust the soot trapped in the DPF. This is accomplished by turning off EGR (higher combustion temperatures in the cylinders) and then adding excess fuel injected during the exhaust stroke where it combusts in the exhaust stream to really roast that DPF at high temperatures.
> 
> I don't know about DEF consumption during regen. It stands to reason that the lack of EGR results in higher NOx generated, and maybe some excess DEF is injected to try to clean up that exhaust stream a bit.
> 
> Then again, the EPA exempts emissions of vehicles during certain engine operating parameters that are infrequent and not a substantial amount of the time that the engine operates. Basically, the EPA knows that engines cannot achieve 100% emissions compliance and they exempt regen cycles because it's every once in a while, hard to control emissions during the cycle, and it's not a major amount of the time that the engine spends operating. If this is true, the ECU could theoretically disable DEF injection because it's a quick 5-minute period of engine operation where emissions aren't controlled due to the EPA exemption.


I'll have to check to see if there are DEF-related parameters I can watch next time it regens out of curiosity. I have always read NOx levels are higher during a regen, which makes sense, and just assumed that would also lead to higher DEF usage. But you might be right that it might not even adjust for those cycles since they are infrequent in the big picture. To be honest even with what I define as frequent regens, it isn't that much of the car's running time. My avg distance between regen is probably around 200-250 at this point, as it does go up and down ... each regen takes about 7 miles to complete ... so that's 3-3.5% of time it's in regen. So even if it did increase DEF during a regen, it still wouldn't be a huge hit overall. We know fuel consumption changes significantly during a regen, and that doesn't seem to make a huge dent in the big picture for me (my last two tanks were 58 and 59 mpg, with two regens each tank).


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## Cruz15 (Mar 17, 2016)

What does your exhaust smell like, does it have a chemical smell at all?


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## Bohner (Nov 3, 2020)

Not that I'm aware of.


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## Carminooch (Mar 23, 2018)

Cruz15 said:


> What does your exhaust smell like, does it have a chemical smell at all?


Mine very rarely does. Sometimes it smells a little bit like cardboard or just hot air. The only time I smell anything dieselly is cold start, followed by the cardboard exhaust smell which usually goes away


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## Barry Allen (Apr 18, 2018)

Bohner said:


> The dealer also tried telling me that there def is better and that's why is using more.


*"A Coke is a Coke and no amount of money can get you a better Coke than the one the bum on the corner is drinking. All the Cokes are the same and all the Cokes are good. Liz Taylor knows it, the President knows it, the bum knows it, and you know it."*
~Andy Warhol

DEF is DEF is DEF. It is all the same. It is all a solution made with 32.5% urea and 67.5% deionized water. It is in this ratio because that is the ratio with the lowest freeze point (12 ºF, -11 ºC) so diesel engines can get the best use out of it during cold weather. EPA regulations require full DEF flow within 70 minutes of engine starting, so there are heaters in the tank to thaw it for use during cold weather.

Anyway, all DEF is the same.


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## Bohner (Nov 3, 2020)

I agree and I laughed in the guys face and told him that I'm not paying 24$ for def. That's why my post also has the lies the dealer tells you


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## spaycace (Feb 9, 2012)

I would have to disagree slightly with the whole "DEF is DEF" statement as it pertains to quality, as that would be like saying Motor Oil is Motor Oil is Motor Oil, and if that were truly the case, people wouldn't talk about how their car runs better with Royal Purple, or Amsoil, etc. DEF also has a shelf life of about a year or so, so if you buy it from a place that doesn't sell much, or has contaminated DEF, then you might have issues as well. When I used the Walmart brand of DEF (to save a bit of money), on my 2.8L Duramax, it threw a code. The dealership drained the tank, filled it with GM fluid (I normally use Peak Blue DEF with no issues). After that one time, I never used that fluid again, and never had another code pop up. Could be coincidence ... could be something else.


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## phil1734 (Aug 30, 2019)

spaycace said:


> I would have to disagree slightly with the whole "DEF is DEF" statement as it pertains to quality, as that would be like saying Motor Oil is Motor Oil is Motor Oil, and if that were truly the case, people wouldn't talk about how their car runs better with Royal Purple, or Amsoil, etc. ...


People also install magnets on their fuel lines and claim they get better fuel mileage. Sometimes they'll even measure and document a difference. Did the magnets really "align the fuel molecules" or whatever the claim is? No. They were expecting a difference, drove accordingly, and got an extra .5mpg on their next tank of fuel.

The placebo effect is real.


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## Barry Allen (Apr 18, 2018)

phil1734 said:


> The placebo effect is real.


No kidding. 

Lately, it's a few news articles where people participating in double-blind COVID-19 vaccine trials are describing their side effects to the public, saying it's some aches and pains but it's manageable.

NEWS FLASH: IT'S A DOUBLE-BLIND TRIAL

None of you people in the trial know if you got the vaccine. None of the people administering the trial know if you got the vaccine. None of you can describe anything because YOU. DO. NOT. KNOW. But the news prints it anyways.


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## spaycace (Feb 9, 2012)

phil1734 said:


> The placebo effect is real.


So ... you’re saying my CEL was a placebo effect from using the Walmart brand of DEF? Wow, I never would have thought about that. Because after I returned to using Peak Blue, I never received the CEL again... unless the dealership disconnected something so it wouldn’t show up again. 
As I said, DEF has a shelf life, so maybe I got an old bottle of it at my local store, but I’m pretty sure my Duramax wasn’t smart enough to be impacted by the placebo effect.


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## MP81 (Jul 20, 2015)

I ran the Supertech stuff from Walmart for years without issue. Only stopped because for a bit, they stopped offering it by me, and now that it's offered again, they won't ship it. Peak BlueDEF they will, so I usually get a few jugs of that to keep in the basement...not that we're going through it all that quickly anymore.


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## DslGate (Jun 29, 2016)

Not that it applies to your case, but my Gen 1 2.0 litre CTD , which has both more HP and torque than the Gen 2 1.6 diesel and mine regularly cruises at 80 MPH (130 kmph) uses about 1 DEF tank per 4000 miles (6,500 kilometers ).


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## Taxman (Aug 10, 2017)

Barry Allen said:


> Anyway, all DEF is the same.


I thought fresh DEF was better than stale DEF. 
But other than the shelf life, yes, it's like saying all distilled water is the same.


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## chevy diesel (May 21, 2020)

I spoke to a garage owner i know and trust and he said don't use the walmart def. Somehow it had caused problems with several vehicles he had to fix over the years. I use blue peak def that i buy with a fresh date code and after 90k miles the advice has been right so far.Having to drain the tank if you have an issue one time would negate any savings you might have built up.


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