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DEF gauge false 30%, frozen?

10K views 15 replies 8 participants last post by  monkeyman 
#1 ·
Hello all! I am new to Duramax and diesels. I have barely cracked 2,000 miles. I have had false DEF readings twice now after hauling loads in sub zero F temps. The first time it dropped to 29% before resetting after a few days. Happened again yesterday after a low of -18F.
Is this common? Could something be fixed/replaced under warranty fix the issue? I'd be pissed if it limited my speed because of a false reading. What % does it start limiting at? I have no way to garage or warm the vehicle. Any advice/tips much appreciated.

Thanks in advance!
 
#2 ·
Just cause it stays at 30% for so long doesnt mean its wrong or the DEF is frozen. If that were the case youd have the DIC display Poor Quality fluid, or Service DEF or Limited Speed.

From the OM.
The DIC will alert the driver when the DEF level is
around 1000-miles remaining range.
Additional messages that must be acknowledged alert
the driver at the 300-mile, LOW and 0-mile fluid ranges
as the DEF tank gradually empties. The fluid level in
the DEF tank must be maintained for the vehicle to
run correctly. If the DEF tank is allowed to run empty,
the system will alert the driver. If fluid is not added at
the next vehicle start, the vehicle speed will be limited
to 55 mph and ultimately to 4 mph in accordance with
federal and state requirements.

& from the OM.
Q. Will DEF freeze?
A. Yes, DEF will freeze—at approximately 12ºF. If DEF is frozen, the vehicle
will start as it always has. After the engine is started, the DEF tank and
lines are electrically heated to ensure adequate DEF delivery in cold
weather. The DEF thaws with no degradation. Remember, since this
system was designed to operate in cold weather, there is no impact on
cold-weather engine operation.
 
#3 ·
Thanks for the reply. The first time it happened I took it to the dealer thinking it was low. They thought it was strange because it was filled when I picked it up new and only had 1400 miles. They topped it off and it only took .25 gallons. It took 2-3 days then reset to OK. I know the reading is wrong, I'm just wondering if I should be concerned and take it in. Would it be a bad sensor or possibly a DEF heater not working properly? The outside temp never got above freezing the first time it reset itself.
 
#4 ·
Normally after adding enough DEF the DEF level % should reset on its own after a few key cycles. If it doesn't then it's a sensor & there is a TSB for said problem. If it keeps happening take it in.
 
#5 ·
I took it in today because the DEF was full and still reading 29%. They called and asked if I had a warm garage/shop to keep the truck in. Since I don't they said they want to keep it inside overnight and it should reset. They said that since it has been under 24 F that the DEF is frozen and gauge is reading wrong but not a problem. I mentioned a TSB but they were unaware of it. What is the TSB? Seems like bs that the gauge on a brand new truck is wrong and doesn't function when it's 24F or colder. It's like that for like 6 months of the year here. Any ideas on what the actual issue is? Thanks!
 
#6 ·
Woodhauler - I have the same problem with my 15' . Three times now when leaving outside overnight in cold weather, even just for one night it freezes and reads incorrectly. Usually starts at 30% and starts counting down towards limp mode. Latest occurrence was this week. After it froze, I had in a heated garage for over night, did not reset, then I drove it for 4 hours, still no reset and still counting down. I was on my way on a 1100 mile trip pulling a trailer through nowhere and had to turn around and head home to my shop. Could not chance going into limp mode.
After another night in a 70 deg garage with a barn fan blowing on the tank - finally reset. When I called my dealer - no one seems to be able to tell me how long it should take for a frozen tank with heaters on to allow the system to read properly. I am scared to leave the truck outside without knowing what to expect.

Telling a customer to put their 70k truck in a heated shop after it sat outside for a night in subzero weather to get it to work properly....

I know GM monitors this and I hope they see it as I have a 17' on order and am seriously considering canceling it unless I can get some answers. The dealer is checking so we'll see what they find out.

I just want someone to tell me what to expect. - Like if it freezes and starts the 30% countdown - X hours of run time should thaw the tank. Should not be reading wrong when frozen to start with.

Love my Duramax but where I live - cannot have this.
 
#8 ·
garagelizard, thank you for your reply. Have you ever had it go into limp mode from a false reading? I've had false readings 3 times now (presumably) due to this cold winter we've been having. All times during towing. The second time I brought it to the dealer they kept it overnight and it reset after sitting in their warm shop. It happened again a few days later when towing. The dealer said it's more likely to happen when towing as it cycles more or something like that. They said not to worry about it as it shouldn't go into limp mode. It reset itself after a few days above freezing. It doesn't seem like any amount of run time will correct the problem if it is sub zero outside but only warmer temps, either while kept inside or warmer days outside. So far I haven't had it read below 28%...knock on wood. I have called another dealer and they said to bring it in if it happens again that it could be a tank heater.

This leaves me with a few questions:
1. Why doesn't it happen to all Chevy diesel trucks?
2. Is it a tank heater or sensor problem as a poster above mentioned? HD DMax Machine mentioned a TSB but the dealer was unaware and I don't know where to reference it.
3. Will it go into limp mode even if it is a false reading?
4. Is there a number I could call to talk to someone at GM directly?

It certainly is discomforting to have my brand new $50K+ truck with less than 3000 miles to have issues that seemingly cannot be diagnosed. I live in a cold climate. I bought this truck because I needed the towing power for my business, but if it becomes too much of an issue it could cause major problems. I really wish I could get a direct answer from GM. I don't have a garage to store it in or heat it up. The dealer I bought it from has pretty much already alienated me. The one I took it to for the issue has been helpful but hasn't given me any real answer. If I was towing and it put me into limp mode due to a false reading I would have a very hard time dealing with this.
 
#9 ·
Mine has only gone into limp once, and I suspect it was because the DEF was really low - this was the first time it happened to me. The other two times - just 30% and counting down - was scared it would limp but never did.

Talked to GM diesel tech today. He indicated the controls know when it is frozen and that it gives you a pass on going into limp mode until the frozen condition is cleared. The countdown is based on usage and not sensors. There are sensors in the reservoir that are in the tank that basically say full, 66% or 33% and any indication of level is based on their being met or not and coupled to usage so not really accurate especially if the tank is frozen.

While he would not guarantee it would not limp - he was pretty sure it would not when in a frozen state.

There is one heater in a cylindrical pick up reservoir in the larger tank in addition to a line heater and one for the pump. Based on this we should only practically expect the pickup cylinder to thaw and not the overall tank unless it gets warm from ambient air or being indoors.

So the bottom line is - will it limp when in a frozen state? Could not get a guarantee from the tech, but he seemed sure it would not.

I have seen GM customer service post numbers to call on here for people having issues. Not sure if this is the same number but this is from a Google search for GM customer service - Customer Relations for Chevrolet - 800-222-1020.

Two last thoughts:

1. remember DEF freezing point is around 9 deg F. and NOT 32 deg F.

2. Next step for my 15' - get heaters and sensors checked though I doubt they'll show anything as I am not throwing any codes and the tech said when he sees them they are throwing codes and something is wrong. He has not seen anyone come in - in limp that does not have something else wrong. This generation DEF system has been in play since 11' so with that many trucks out there you would expect if freezing sent to limp he would have seen it.
 
#10 ·
I've seen this false gauge thing roughly correlated to freezing temps, so I am skeptical the DEF freezing point is that far below 32F. I'd say more likely closer to 32F just like water. JMO.
 
#11 ·
I just went through this while heading to the mountains 10 days ago sledding. Read 30% on the highway just before I filled up with fuel. Pulling into the gas station it read 29%. I dumped a 2.5 gal jug in and it read 28% and froze there. I jumped in the truck this morning and it still read 28%. Got a little ways up the road and checked it again and it read ok.

I suggest just filling it up and driving the truck. If it doesn't read ok after it warms up to -5c for a few days then go to the dealer.
 
#12 ·
Thanks garagelizard that is helpful info. Its somewhat reassuring that it wont go into limp from just reading low due to being frozen and not actually being low on def. It does seem that GM have stopped short of giving a definite answer on this. What they told you is consistent with what the dealer told me. Knowing that a full tank of DEF should last for 4000-5000 miles it shouldn't be too hard to differentiate a false/frozen reading from actually being low. I'm certainly not going to top off with .25 gal of DEF everytime it freezes if I've only gone 500 miles sine the last fill- which I've already done twice. I live in a cold climate. I bought my truck to haul loads which is what seems to set this off, more than not towing. We have weeks go by where it hasn't got above 5 degrees F. I don't have a heated garage so thawing is not an option during extended cold spells. I can live with a false reading as long as it doesnt go into limp. I know at some point I will be on a long trip while towing, the DEF will freeze, I will top it off and pray. Added stress while hauling on icy roads is not ideal. It will be interesting to see if it ever reads below say 20% because it is frozen. The dealer told me it doesn't limp until it is almost empty. Kind of disappointing that GM can't fix this or give an accurate explanation of the problem. Is there any reason they can't make DEF that doesn't freeze? It's 2017, I'd think the technology is there. Until then I'll hope for warmer days. Its the 6th night of sub zero temps now and it is still reading OK, presumably because I haven't been towing. I still don't understand what makes it happen only while towing.
 
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#14 ·
Woodhauler - the only thing I can think to add is I have noticed DEF consumption is greater when towing which I think would make sense since you have your foot in it a bit more. Maybe something to your assessment of towing being a trigger. I tow a lot from the Midwest to Western states in cold sub zero weather so definitely feel your stress. Not the time to have this happening. I think GM would have a huge liability if they addressed this head on - hence the avoidance and our experience.
 
#15 ·
2016 - 2500 Silverado with 2400 miles on it - 57 hours on the motor...While trailering a 29' - aluminum 4 place snowmobile trailer from Pittsburg NH to Saguenay Quebec in 28F weather the cluster reads DEF level is @ 30%. Not a big deal, pull over and top off the fluid. 150 miles later & 2 -3 on off engine cycles the DEF gauge still does not register full but had dropped to 28%.

Fortunately Arnold Chevrolet is located next to the hotel in Saguenay. After dropping the trailer I drop in unannounced hoping they tell me to turn the key and press the pedal a # of times and it will reset. NOT ! The service writer informs me it doesn't work that way. A technician was required to reset the gauge by means of computer. I am told that was the only way. A 1/2 hour labor for a total $ 65CAD + - and my gauge has been reset and I am out the door. The service manager told me to claim the $ with my dealer when I return to the states. I'm happy as ARNOLD Chevrolet dealt with my issue immediately with no messing around as it was near closing time when I stopped in.

Return trip to the States was uneventful albeit the temp was 32F....The latter very unusual for this time of the year in the territory we were required to drive through.....Set the cruise at 60MPH and didn't even know the trailer was back there : ) while we dipped in and out of the hills between Saguenay & NH.
 
#16 ·
Here is a quote from makers of DEF, in response to an email I sent, Rick
Hi Rick,
DEF works with a catalyst and is delivered into the exhaust system, adding anything is likely to damage the catalyst and it will need to be replaced.
DEF shouldn't freeze until -11c (12.2F), but if it's colder than that where you are, then there are some products that have an anti-freeze element, although strictly speaking those aren't DEF.
You should speak to your local dealer for more info where you are.

Thanks,

Adam
 
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