The gauge has nothing to do with how far you can drive. It’s a guess of the tank’s level, at best. What drives the mileage is how much fuel you’re using. High speeds or loads will run thru DEF a lot faster. I can go months driving around town and to/from work unloaded. If I pull my boat (4600 lbs), I’ll get the 1000 mile warning after about 400 miles or so.

I hear the LZO’s get less DEF mileage than the LM2’s but mine is a LM2. Not sure your driving.

Lots of DEF discussions on here.

 

2021 LM2.

Average 68mph. Lots of headwind this trip. Average has been about 11.2mpg.

So are you saying to ignore the dash messages entirely and just drive? It seems like I should be able to get about 850 miles to a tank of def.
My only complaint there is the def message that you can't get rid of so you're unable to see any of the information on the dash.

I also agree, around town with no trailer there are no issues.

 

What brand DEF are you using? 🤔

 

Jugs are off my shelf in my shop from my vendor I buy from. I sell jugs, and bulk. Brand varies, but I know it's quality stuff. I have a couple customers that buy a pallet at a time and have never had an issue.
Pump def if I'm traveling is from pilot, loves, or bucees.

 

Just curious if was Platinum or not. I use only Blue DEF or pump ( same places you mentioned).

 

Wanted to update, I currently am selling Tartan DEF. That is also what goes in my LM2 from jugs as needed.

 

LZ0 does seem to use more def than my LM2 I was using 4 to 5 percent (DEF/FUEL) with my LM2 and so far 5 to 6 percent with my LZ0. To be fair my LM2 had 50k+ on it and my LZ0 only has 4500 and I am pushing the LZ0 harder through the rockies (montana, wyoming, utah) we'll see if it eases up across nebraska, and missouri. Yes, you can just keep driving it, I drove mine until it was limited to 65, it acts like cruise control, just won't go over 65 even with foot on floor, I only drove it speed limited for about 50 miles until I found fuel.

 

Seems high percentage considering I’ve done exact calculations with my LML 6.6 and it uses roughly 2% of fuel used. 9.46 L used to 435 litres of fuel used equates to 2.1 percent.

 

DEF is not like Gasoline, brand type is pretty much irrelevant, the usage depends on loads, higher loads, more usage.

The tech aspect of the DEF is for the SCR and the DPF is after that. Most people believe the DEF is used on the DPF and used during Regen, that is not correct. The DEF is injected before the SCR, after that the DPF and uses Diesel to increase the temps for regen.

So, the lighter the loads and speed the less DEF and less Regens.

On empty, I can go 846 miles before a regen and the DEF last a long way. When towing my 43 footer 5th Wheel, all is cut by half and I try my best not to flog the engine.

 

Check the MAP sensor, on the L5P the sensor gets gummed up with soot from the EGR dumping gases in the intake. Take a look at it and see if is dirty, clean or replace if need it.

Keep in mind, the DEF consumption depends of the load. If the computer sense a high load, the more "pig piss" is dumped. 😏

 

And here all along I thought it was cat pee.

 

DEF use will increase when towing for two reasons:

1) NOX cleanup requirements are proportionate to fuel use, which is higher when towing.
2) Heavy loads shift the responsibility of NOX cleanup/prevention from EGR to DEF/SCR. EGR use will be curtailed above moderate load. Higher load means less EGR. Less EGR means more NOX. More NOX means more DEF/SCR. As such, when towing, the amount of DEF used relative to fuel will increase.

This is true outside of the babymax platform and easily observed.

The connection of DEF use to active regens is related. Most platforms will also pause EGR use during regens in order to send as much oxygen (and heat) downstream as possible. This helps kick off more heat in the DOC but the oxygen is also needed for the regen "burn" in the DPF. This leads to higher tailpipe NOX unless the DEF consumption is increased during the time of the active regen.

So yeah, heavy load conditions will consume more DEF and disproportionately more than just the increased fuel consumption.

 

My sarcasm is kicking in and I say, remove the pesky thing and save the environment by properly maintaining the vehicle with good driving habits.

 

Exactly this. I wonder if the environmental benefits of the DEF/SCR system even equal the environmental impact of the manufacture (and eventual disposal) of said components, including the DEF bottles/packaging...

 

Good afternoon folks;
I haven't posted anything here yet but I have been reading these posts.
K&P is correct in mentioning that the DEF system is pesky (downright annoying actually), I live in Manitoba and 3 years ago I broke down and bought a low mileage 21 GMC with the 3.0 duramax,
I don't really tow anything with the little guy so DEF usage really wasn't much of an issue but I didn't like it anyway. We drive out to Vancouver Island once a year to visit family so I had the truck set up as our travelling truck. High flow air intake system, I found a Bedrug box liner, good tailgate seal and a tonneau cover which turned the truck box into an almost dust free car trunk. (we have lots of gravel roads to drive and without the bedrug the truck box was a dirt nightmare).

Last October I decided to bite the bullet and get my truck deleted and tuned, the cat and dpf filters were removed, race pipe put in (straight pipe), tuned with an extra 50hp and boy did she sound sweet, was still a lot quieter than most trucks with performance exhausts and at highway speeds couldn't hear it at all.
Pulled really nice and I was so looking forward to checking fuel mileage and performance this year on our BC trip, BUT, that didn't happen.
April 19th on our way to a wedding reception we got T-boned and sadly that spelled the end of our truck.

I finally managed to scrape together enough money to replace it with another 21 GMC 3.0 but I can't afford to set this one up properly yet,
One thing I do know, no more weddings for me, just can't afford them.

For pulling a trailer I run my 08 Silverado LTZ- Z71 with a GFX package, 6.6 Duramax, deleted and tuned pulling aluminum trailers for my Kubota KX 121-3 mini excavator.

 

I would be very interested in links to the products you mentioned for sealing the bed. I have the carbon pro bed and a tri-fold tonneau on a 21 GMC 3.9 mini-max.

As for DEF I have learned to have at least 5 gallons of spare DEF at all times when pulling the 6500 lb trailer. Have not gone through the process to determine percentages. Get approx 12 mpg with trailer (AT4 increased height/drag).

 

The secret to never seen engine light def light ……. I have a 2013 Chevy Silverado 3500 HD I pull a fifth wheel which is about 18,000 pounds had numerous problems with death limp mode turbo veins .. fully 50 horse tune CP three conversion 63 mm blade turbo upgrade boost pipe lift pump 5 inch stainless steel exhaust no muffler. No more problems and I’ll probably get 500,000 miles instead of 250,000 when I took the EGV out of the valley that was going back into the engine was unbelievable good luck the money was well worth it in parts to have peace in mind good luck my friend and the power and the sound is like music to my ears

 

All this talk is a fancy way of saying GM has a problem with their computers that they need to fix. I don't compute or calculate. I don't really care. I bought the truck because it should be able to complete a task well and it does in pulling a 6000lb camper.
I like getting 30+MPG on the highway with no trailer, it's a smooth driving truck and checks all the boxes. Without the camper behind me, I don't even pay attention to the DEF. I don't drive it enough to fill the tank once in a year. Except for our camping trips where it gets filled more often obviously.

The DIC being completely blocked by the DEF empty, XXX miles to 65 is frustrating when I know there's still 2+ gallons of DEF in the tank.

So here's how I understand it and here's an easy fix for GM. With no load (trailer) DEF can go thousands of miles. Getting that 500 miles to 65 is a great warning to add DEF. (It would indicate maybe 10% or less left in tank, or empty as the DIC states)
When pulling a trailer 500 miles leaves half a tank of DEF and is way to soon to be alerting the driver.

So why can't GM add a float to the def tank, so they can accurately know how much DEF is left in the tank?
Or fix the DIC so it's not locked out at 500miles...how about 50 miles?

 

Nicely stated but it’s not GM’s problem, it’s what the EPA requires and Trump fixed that going forward but that’s not going to help us

 

This might with management of def fill / refill issues.

Unable to Fill the DEF Tank – TechLink

gm-techlink.com

Unable to Fill the DEF Tank
October 31, 2024
The Diesel Exhaust Fluid (DEF) tank may appear to be empty shortly after beginning a towing trip or it may be difficult to properly fill the DEF tank on some 2020-2025 Silverado 1500, Silverado 2500HD/3500HD, Tahoe, Suburban, Sierra 1500, Sierra 2500HD/3500HD, Yukon; and 2021-2025 Escalade models equipped with a diesel engine (RPO LM2, LZ0, L5P). Under high load towing conditions, the amount of DEF used may engage the DEF warning system before the DEF system can read the tank has been filled. If the tank is filled under these conditions, the DEF system will not see the fill and may not see subsequent fill attempts. (Fig. 5)

Fig. 5

The vehicle should be driven to allow the DEF warning system to progress until a specific speed limitation warning is displayed on the Driver Information Center before adding DEF to the tank. In the U.S., the speed limitation will be 65 mph (105 km/h).
TIP: Refer to Bulletin #22-NA-150 to verify the Reductant Control Module is has the latest update available and that the Reductant Fluid Tank Level has been reset.
The DEF level also can be exacerbated by vehicle loading that exceeds the Gross Combined Weight Rating (GCWR) when towing. Reference the towing label inside the driver’s door and, using a commercial scale, confirm that the total weight of the vehicle, trailer and cargo does not exceed the GCWR.
DEF Warning Strategy
When the DEF warning strategy is implemented, it is based on an estimated range to speed limitation of 1,000 miles (1,609 km). When the gauge is reviewed during the warning strategy, the gauge will show very little DEF or no DEF at all. This is a normal condition. The DEF system needs to complete the warning strategy (Fig. 6) and inducement is not shown on the gauge. Only the reserve level is displayed in some cases. With large trailers, there may not be a reserve and there will not be any gauge bars displayed.

Fig. 6

Do not immediately add DEF when there is a DEF system message and a low gauge reading in order to drive the gauge back up or to remove the DIC message. The following chart (Fig. 7) shows the DIC messages that may appear while towing and the messages in red where it is not appropriate to add DEF to the tank. Areas in green indicate that at these warning levels and when these messages are displayed it is OK to add DEF to the tank.

Fig. 7

Customers should be encouraged to not fill the DEF tank under these conditions until the warning strategy indicates a specific speed limitation will be reached (65mph/105 km/h). When the system message changes from “Speed Limited Soon” to “Speed Limited to 65mph in xx Miles” it is safe to add DEF and the fill will be detected. The messages may stop for a short period, but they will begin again shortly if the vehicle is still towing. The vehicle can continue to be operated until the DIC message is displayed that inducement and speed reduction are imminent. This is technically the best time to fill the DEF tank, and the system will register a fill at the inducement level if DEF has not been added during the warning strategy and there are not any functional issues with the DEF system.
TIP: When adding DEF to an empty or very low tank, always add at least 2 gallons (7.2 L) of DEF to release the vehicle from speed limitation.
Check out Bulletin #24-NA-196 for more information.

 

So you are saying you should add between five and 6 on the warning chart?

 

I think what Techlink is saying is don't be constantly topping it up.
Let it get really low before adding def.

All to avoid messing up the range estimate set-up.


My additional comment is that speed limit does not happen when it reaches empty.
When it gets to empty is when it starts a 500 mile to speed limit countdown.
This is not a range estimate. It is a countdown of odometer measure miles.

I've taken both 6.6 and 3.0's to empty and the 500 mile to speed limit countdown (intentionally) -- just to verify that the screens work that way.


Side note:
The 2011 did not have any kind of def level indicator -- it just gave the 1000 mile warning and the 300 mile warnings.
Made me very comfortable with waiting for the warnings. I did not take the 2011 to empty.

2012 -2016 LML had an indicator that said 'DEF level ok' anytime the level was above 30%. This meant def level was only a guess unless it was less and 30% remaining -- and probably encouraged not filling early.

I still never add def if it is above 30%.


These were on LM2

 

Edit Expanded my search to the whole forum and not just LM2/LZ0 section.
Apparently this is going to be annoying and frustrating. The DIC will be blocked once I get the 500miles to empty message and I can't fill the def tank until that hits 0...

That's not the way it's supposed to work.


It should give a def level notice (once) when it is somewhere around 1000 miles of estimated range remaining.
When estimated miles to empty is below 300, it should give notice at each startup.

When it thinks it's empty -- that is when it should start a '500 miles to 65 speed limit' warning. (not a 500 miles to empty warning)
This warning is the one that takes over the screen and cannot be cleared. (further incentive to add some def)
Two warning screens alternate when this is happening.



If it's an emission system hardware issue rather than a def level issue the warning escalation setup is different and may also be a fewer number of miles.

 

Mine does exact same thing I fill it and it takes very little and message pops up

 

Alright, so here's where I'm at now. We're back home from our trip and I've got the DEF empty message locked on the DIC. It's got 397 miles until max speed 65MPH.

I can safely assume I've still got around 2 gallons of DEF in the tank.

I'm not pulling the trailer again until mid October.

Do I commute to and from work with this message on the DIC now or do I fill the tank to clear the message?
There's enough DEF for another couple thousand miles, but the computer can't identify the change in fuel usage and it's already locked into DEF empty mode. So even if I wait out the DIC message I'm still getting MAX Speed 65 in less that 400 miles...and nowhere close to an empty DEF tank.

 

Alright, so here's where I'm at now. We're back home from our trip and I've got the DEF empty message locked on the DIC. It's got 397 miles until max speed 65MPH.

I can safely assume I've still got around 2 gallons of DEF in the tank.

I'm not pulling the trailer again until mid October.

Do I commute to and from work with this message on the DIC now or do I fill the tank to clear the message?
There's enough DEF for another couple thousand miles, but the computer can't identify the change in fuel usage and it's already locked into DEF empty mode. So even if I wait out the DIC message I'm still getting MAX Speed 65 in less that 400 miles...and nowhere close to an empty DEF tank.

I would go ahead and add a 2.5 gallon jug of DEF in and see if it works itself out. Otherwise, a dealer trip may be in order.

 

With the first, dismissible message, you can drive and the mileage increases every trip but once you’re into the locked DIC it stays locked towing or not. The only way to unlock is to add DEF

 

Unfortunately this little engine produces so much NOX and uses so much DEF, under heavy loads they have to do all of these warnings so you don’t empty the tank before you get to the final warning. This is why the larger Duramax don’t use nearly as much DEF. About the only answer is to find a larger DEF tank. 🙏

 

there was a recalibration the dealership did for my def gauge and has been right for the most part ever since. was a real PITA, especially when I was filling up with the jugs instead of at the pump.

 

there was a recalibration the dealership did for my def gauge and has been right for the most part ever since. was a real PITA, especially when I was filling up with the jugs instead of at the pump.

 

You could always get an empty jug and fill it at the truck stops as a backup when towing long distances. I haven't run into the situation towing yet but will carry a new jug just for peace of mind.

 

What about DEF shelf life? I had some AdBlue stored as an emergency supoly for about 3 years on an dark cool area and seems to be ok; just used it the other days just to rotate the stock. I read somewhere that has a life span of 2 years.

Where do you guys store the DEF and for how long?

 

I store mine in the garage. In 22,500 miles, I've had to add 7.5 gallons. I don't keep it too long since I've only had the truck a little over a year. I think the dealer topped it up once during an oil change. I always add when the gauge show 1/2 full. I usually pick up two jugs at a time from Costco.

 

Most every where you can buy fuel will also have DEF.
When it was introduced 15 years ago this wasn't true.

With all the warnings before it gets empty, and 500 miles after it's empty, before speed limit occurs it shouldn't be necessary to carry def.

Pretty good chance if it didn't need def at the last fill, it's gonna need fuel before the 500 miles -- and def will be available.

 

Most every where you can buy fuel will also have DEF.
When it was introduced 15 years ago this wasn't true.

With all the warnings before it gets empty, and 500 miles after it's empty, before speed limit occurs it shouldn't be necessary to carry def.

Pretty good chance if it didn't need def at the last fill, it's gonna need fuel before the 500 miles -- and def will be available.

May be true up north but not anywhere around here. Truck stops? Yes. Normal "gas stations"? Not so much. And at truck stops, at least the ones I've been to, you have to use the big truck pumps to get bulk DEF. Not available at the regular car pumps even though they have diesel.

 

I did add one 2.5gal jug of DEF on Saturday. It cleared the DIC. DEF gauge currently shows full bars. All messages have gone away. I am traveling unloaded with it this weekend and anticipate no problems. Once I'm back in town I will schedule an oil change and check in on making sure everything has the most current updates.

The only thing to do now is wait until we travel in October with the camper and see how much trouble we have with the DEF messages.

 

Just completed an 8,500 mile road trip. What I found is that truck stop are much more expensive in the 11 states I hit. Most truck stops were around $4.25 per gallon. Rural king had the boxes for $6.88. Walmart within a buck.