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Too Hot Too Cold HD Denali


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Update, new "feature" determined. Been having a heck of a time getting the windshield to defog. Set the Climate Control to "DeFog" which is defroster (windshield) and feet. Didn't seem to matter what speed I set the fan or the temp to, window wouldn't clear.

 

Tonight was a nice ice storm, and so the issue was more acute as we were heading home in the dark and stormy night. Bad enough that we were checking further to see why things were so goofy in the truck. Turns out we are getting no air out of the defrosters in DeFog mode.

 

Put it in DeFrost mode (which is windshield and side window outlets only) and we are getting air out.

 

That would explain why I couldn't get it to defog the front window in normal "feet and windshield" mode as only the "feet" portion is blowing air. So, we could either have a clear windshield and cold feet in DeFrost mode, or we could have warm feet but not be able to see out the windshield in DeFog mode.

Tried AUTO mode too, but it wouldn't put any air out to the windshield.

 

Anyone else's truck do this? I'd really like to hope this is just a malfunction and not a design condition. Last time in the dealer for similar issues, Tech indicated "working as designed". Have to point out the "no defroster in defog mode" was not discussed at that time since we just figured that out tonight.

 

Very disappointed in this machine.

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I have a 2016 3500 Denali Duramax. I've only driven it a few times (a little over 1,000 miles) but my system seems to work fine for me. I primarily use AUTO mode but I've also used manual. I typically set it to AUTO then turn A/C off. In all modes, it seems to work fine. Ambient temps from 20's-40's. All drives have been more than 30 minutes with most 3-4 hours. So far I'm very impressed with the rig. Of course, it's only been two weeks.

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If it makes you feel any better I HATE auto mode, I don't want the fan blowing like crazy for no reason, I don't even want to hear the fan or have it drying out my contacts, if the heat is on the fan is turned all the way down and on my feet.

 

Besides that auto mode seems to run the a/c non stop and there is no reason for it.

 

FWIW - on auto the fan mode on start up can be preset to your choice (in settings) until you touch any heater buttons, so the fan won't ever blow on high if you select it

 

same with radio volume on start up ...

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I have a 2016 3500 Denali Duramax. I've only driven it a few times (a little over 1,000 miles) but my system seems to work fine for me. I primarily use AUTO mode but I've also used manual. I typically set it to AUTO then turn A/C off. In all modes, it seems to work fine. Ambient temps from 20's-40's. All drives have been more than 30 minutes with most 3-4 hours. So far I'm very impressed with the rig. Of course, it's only been two weeks.

 

 

Great to hear that it may just be this truck. Would love to hear how yours behaves in manual mode, to see if consistent temps are emitted through a driving session.

 

If it is something "fixable" on mine, then there is hope. The more I read about [other brand] that I was considering as an alternative, the less happy I was. Would really like to stick with GM here....

 

I spent some time with it in the garage tonight and I could get air to come out on the windshield in defog mode, though I had to crank the fan to 80%+ to feel it. Starting to wonder if we just were not reaching into the center of the defroster vent to feel it while driving, or if there is something related to being in motion that is causing it to not work.

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I have a Denali 2016 and i do not have this issue... if i set it to 72 or 74 it's the same temp from top/vent/feet... and it never changes... i aslo don't like the auto... so i use manual and it's basically exactly what i set it to.

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  • 1 month later...

Update. Truck been to dealer 2x for this issue. First "no problem", second temp/solar sensor replaced.


Truck seems a little better (less variance across the board) but drivers floor gets way hot. Set for full AUTO @ 70 and the drivers floor is hitting 84F (have seen 90) while the passenger side is down near 70 like it should be. Dual zone set for SYNC.

Following graph shows temps in the cab at various locations. I'm seeing wide swings on the drivers floor relating to vehicle speed. Dealer is planning to replace one sensor down there, but I'm wondering if it's something else. Is there a motor or diverter that is failing with higher vehicle speed (too much air pushing that door open or)?
hotDriverFloor.png

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For reference, here's what this truck was doing before they changed the temp/solar sensor. It's not a great comparison to the above as the test locations/conditions were not exactly the same, but the wild fluctuations are pretty visible throughout the truck:

 

mrToadsHeater.png

 

 

 

 

This is what I am comparing to, what I consider "normal". This is one of the loaner Sierra 1500s I was in (SLE trim). This compares exactly to the first graph above, same location/conditions/temp settings. Only difference is trim level and that's important because the SLE was buckets with the center jump seat, so no console separating drivers and passenger side.

 

goldStandard.png

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Truck is back at the dealer (3rd time). Called GM and they were less than helpful.

 

Recent trip had me in the cab for about 16 hours. To describe the drivers floor temperature as "miserable" would be generous.

 

In case somebody else's truck ever fails in such a way, here's what I did to keep it tolerable:

Run at AUTO until floor was too hot.

Set air discharge to be dash-only (this effectively shut off the floor vent, not entirely, but close).

Close the dash vents on the drivers side. Drop the drivers temp to 66 and set the passenger side to 68. Obviously the passenger won't be happy (and I didn't have one) as it will be pouring hot air out the passenger vents with a vengeance.

Flip back to auto mode when your feet get cold and repeat.

 

One other tidbit, on the first leg of the trip, the temp was 37F outside. During this time, the HVAC performed perfectly. It usually takes ~20 minutes of drive time before I can see the temps start to deviate on the graphs and this time it was into about 40 minutes and right where it should be. Shortly after then, the temps dropped to 28F and soon as they hit 35 the drivers floor started jacking up. Only had one time where those conditions were met, so it's not definitive, but it was interesting and ties into the "seems OK above 40F" that I noticed previously.

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Received truck back from Dealer. They replaced HVAC Controller. Drove truck home, within 20 minutes, same song and dance. Set to 70 and AUTO. Drivers floor at 82, passenger at 72. Keep going and drivers side floor (ie my feet) are up to 86.

Pretty disappointed. That was third time in for this item and now 28 days in the dealership out of ~120 of ownership.

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  • 2 weeks later...

Dealer contacted and asked me to bring in truck for them to work on it further. Indicated they were brining in a "GM Engineer" (in quotes 'cause I don't know the details, allegedly this person works on the engineering dept that is involved with the HVAC system).

8 days later, they changed out the HVAC wiring harness and associated sensors. This fixed an issue they were seeing with diagnostics in the shop. I took it down the road and it failed within 30 minutes (set to 70F/AUTO and drivers floor was at 80F; pass floor at 72).

 

Took it back, took Tech for a ride, showed him.

Went back, got another HD off the lot, but it was an SLE, not a Denali, but was 2500HD with Duramax (new). Ran it on the same roads/patterns and it did NOT fail, worked great. So.... Dealer is a bit stumped. Needed to review and do some more thinking on what else they may be able to do.

 

I've started arbitration process, hoping GM will replace the vehicle. Been in dealership 36 days out of 139 days of ownership; 4 attempts to fix this one specific issue (besides other problems).

 

Couple of tidbits gleaned from the Tech:

 

1. The HVAC system no longer samples internal temperature after initial start up (this is by design). The solar/temp sensor on the dash is read right when the vehicle starts and then is ignored by the system as far as temperature. In fact, you can see it on the tech's computer system, it will read the correct temp (say 45F) when the truck starts and then shortly after it will go to some goofball number like 954F.

 

Tech indicated that the Engineer told him there are no further "general" temp readings from inside the vehicle after that initial first read. The HVAC system bases it's output on the temps reported by the outlet air sensors (how hot the air is coming out of the vent, at the vent). That seems, well, dumb, for a system that is supposed to be fully automatic and "magically" maintain a set temperature, for example what if I have 3 passengers or a window down?

 

2. The Duramax trucks have an auxiliary electric heater in the HVAC system. He did not know the operation nor how/when it kicked in. We could not see it in his diagnostics. He saw the wires running to it when changing out the HVAC harness and was confirmed by the Engineer. Since this truck does not blow hot air instantly, (takes a few minutes to warm up like every other vehicle) I just do not see how it could have something like this. It makes we wonder if that was actually the DEF tank heater being referenced, but seems weird the harness would pass through the inside of the firewall to get there. Dunno.

Ford lists this type of aux electric heater as an $300 option, but I've not seen anything from GM on it (feature or option).

 

Another note, but not directly related to this thread:

 

Set the cruise, set the exhaust brake, now accelerate above the cruise set point and then release the throttle (like you passed a car but left your cruise "on"). The truck will downshift and engage the exhaust brake to return to the cruise set point. If you set the cruise at 60, accelerate to 80 and then let off, it will downshift at least 2 gears (tach at 4700 from 1500 during the downshifts) to get back to that set speed.

Confirmed this as a "feature" with that other 2016 HD. Best to describe it as "aggressive deceleration".

My 2012 does not do this, it will do as you expect, just coasts back to the cruise-set-speed.

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  • 1 month later...

Final update on this....

GM Engineer evaluated truck, compared it to a similar truck (Denali) in the service bay and found they worked identical. Which is expected to me, I've not seen any issues with excess heat when the outside temps are upper 60s as it was inside the shop. We took mine for a drive, outside temps around 30F and saw one of the bigger issues I have with this truck - set to 70 and AUTO, the drivers floor exceeds 80F when driving at highway speeds. We didn't continue to see how hot we could make it.

They did not drive the other vehicle to compare it to, but felt that it would act similarly.

 

Bottom line, their position is the vehicle is performing as a similar vehicle. Nothing to fix. Note they didn't state it was "working correctly".

 

They did offer to possibly re-route the output of the driver floor vent to alleviate some of the temperature. To me, if we did that, we'd just shift that DS Floor temp pattern down, but it would still follow that graph, so we'd just end up with super cold temps for shorter trips and maybe adequate temps for longer trips. Not a solution that is palatable for me.

Just for reference, here's a graph showing a comparison of the 2500HD SLE and this Denali (see above post when we did this on a previous date).

 

Same outside conditions, vehicles driven back to back over the same roads, same speeds. It was highway speeds for 50% and then expressway speeds. Travel west, then north, then east and reverse.

Ignore the first ~7 minutes as the vehicles are getting up to temp and on the road.You can see a little fluctuation on the SLE for a couple of the temp points, but we're talking 3F changes, nothing notable. The Denali, on the other hand, is bumping around and going "way" high on the drivers floor with a much bigger overall difference between temps.

The SLE does not have a center console, while the Denali does, which they felt would make the issue act as it does. As they declined to drive the other Denali and I didn't have my instruments with me anyway, I don't know 100% if "they all do it" or not.

 

The last loaner they had me in was an 2016 Yukon SLT. I did temp recordings in it. The temps don't look like my Denali, but they also swing more than the SLE. Still no manual operation, it's either AUTO mode or expect wildly swinging temps if you try and set the output and blower speeds (saw 92F on the PS Floor when set to 68F, floor and defrost, 30% blower).

SLEvsDenaliComparison.png

 

I've wasted way too much time, endured way too much stress, lost trip time since my tow vehicle was in the dealer and generally been excessively disappointed in this truck to continue fighting with this one. Hopefully I can find a truck I like as much as my 2012 Sierra in a different brand.

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Sounds like the system is over-controlling. When it tries to increase the temperature the system opens up the heat, waits, opens more, waits, etc. Similar for cooling. With the fan speed set so low the cab temperature isn't responding fast enough. Probably isn't as severe at highway speeds when the air is being forced through the system.

 

Increasing the fan speed would probably help.

 

Auto mode - there is a setting for the maximum allowable fan speed in Auto mode. Allows the user to make the ultimate decision - fan noise vs fast heat/cool response. Great idea GM!

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Sounds like the system is over-controlling. When it tries to increase the temperature the system opens up the heat, waits, opens more, waits, etc. Similar for cooling. With the fan speed set so low the cab temperature isn't responding fast enough. Probably isn't as severe at highway speeds when the air is being forced through the system.

 

Increasing the fan speed would probably help.

 

Auto mode - there is a setting for the maximum allowable fan speed in Auto mode. Allows the user to make the ultimate decision - fan noise vs fast heat/cool response. Great idea GM!

 

 

In manual mode, increasing the fan speed will cool things down (when in heat mode), in my testing. Counter-intuitive, usually increasing the airflow in a heating situation will produce more hot air.

 

In Auto mode, with the tech's computer hooked up, we could watch all of the truck's sensors and input. We could see the output temp increase on either side. Never really watched what the fans were doing closely, as they didn't appear to be doing anything wrong. They did watch the air doors, but that was more for about watching to see if they moved when commanded to do so. Not sure they watched air door/fan speed/temperature output closely to see if there was any over-distance correlation.

 

In testing with the engineer as well as the tech in the truck, we never could explain why the continued increase in heat on the floor. We could see what the computer was doing and that the sensor temp points at each duct where changing, we could see that with a forced change on the settings (changing sun load or changing the temp dial up/down) but again, never why it would keep building heat on the floor.

 

Well, we have an idea, but nobody would say it (bad engineering).

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Yesterday, I was able to resolve the issue with the HVAC system in this 2016 GMC Sierra 2500HD Denali...

 

Dealership had it for 42 days out of the 172 days that I owned it.

 

Truck had the fuel injector pump replaced and at a later date the turbo inlet gasket was replaced. There were unburnt diesel fumes in the cab for these two repairs.

The HVAC issues cropped up about a month after I owned it. I got the truck in mid-October and we had a warm fall, so the temps were in the upper 60s for the next couple of weeks and slowly worked towards the 40s in Nov. That was when the issues started to become noticeable.

 

The dealership subsequently replaced the solar/temp sensor, the HVAC controller and the HVAC wiring harness with all sensors trying to correct the HVAC related issues (see graphs posted earlier in this thread for a visual of what it would do). Those graphs don't show how the system will change from putting heat on the floor to blowing cold air out the dash vents because the sun came out from behind the clouds as you were driving, even though it's still 30F outside and no temp changes happened in the cab. Well, then it would get cold in the cab as the system made a change based strictly on sun load.

With all of those repairs, there was just a small difference/improvement in the overall "whackiness" of the system after the solar sensor change. The Techs noted "fixes" when testing in the shop when the other two repairs were performed, but the customer experience did not change. The system really acts up the longer it's driven at higher speeds (above 55, longer than 20 minutes).

 

I had started arbitration with GM, asking for a replacement vehicle. I had presumed it was "just this truck". They couldn't all be like this. All of the SLE trim trucks the dealership put me in while the Denali was in for repairs worked fine in my "felt like" and actual temp recordings. They didn't have center consoles on the floor, is that related? They also didn't make sudden changes because the sun hit the dash (whether coming out from the shadows or when we turned travel direction). We're talking 2500 miles combined in these SLE trucks.

 

In a strange twist, on the last round to the dealer, as part of the arbitration process (which GM failed to notify the dealership, so I had to sit there for 3 hours while they found me a loaner), the dealership put me in a 2016 Yukon SLT. This was the first other "new" GM with SLT or Denali level trim that I had to compare with.

 

The Yukon was more "calm" than my Denali as far as rapid HVAC changes in AUTO mode in the 500 miles I put on it. However, it still did not perform as expected.

 

Here's a graph showing 70/AUTO and it's in the upper 40s outside. The start of the floor temp increase, at the 9 minute mark, happens when we change from east to north (it's 11AM) which changes the amount of sun hitting the solar sensor. The drop at the 31 minute mark is me clicking it from 70 to 69 (my feet were getting uncomfortable).

 

16YukonAUTO.png

 

Below is the same Yukon, on a different day, with 4 occupants and we tried MANUAL mode. Set it to floor and defrost, 69F and second to lowest fan speed. I didn't document the rear HVAC settings, but they appeared to be mimicking the main settings. It's 30F outside, bright, light snow. Note the drop at the 42 minute mark on the PS Floor - Passenger changed the setting for their side from 69 to 65 as they couldn't stand the heat on them any longer. Can't blame them, they had 92F blowing on their face 5 minutes into this ride.

Looking at the graph, you can see the only thing remotely close to the number we had it set to was the ceiling (passenger visor).

 

16YukonMANUAL.png

 

Based on this data and drive time in the Yukon, I started to fear that a replacement Denali was probably not going to fully resolve the HVAC-related problems I was experiencing. I was documenting high floor heat on this similar trim, but different vehicle; still not able to use manual mode with any hope of it doing what it was set to and other hard-to-document inconsistencies.

 

So, after the engineer saw the high floor heat and determined that my Denali "performed like similar vehicles" I went to the Ford dealer and test drove an 2016 SuperDuty F350 Crew Cab PowerStroke (Lariat/Platinum trim). Drove a King Ranch first and ran it through a half hour ride and noted the HVAC appeared to behave (my Denali trained me to watch specific things, which is sad). Ran the Denali through the same "course" immediately afterwards and it did it's normal hot/cold sun/no sun changes. Ford stayed consistent. For my own well-being, we did an overnight test drive with extended expressway time to ensure the Ford would work "as you think it should", no concerns found.

 

Here's a recording in manual mode, 30F outside, set to 68F inside, sync'd, manually set to floor and defrost, lowest fan speed. Most of the previous graphs give an 5 minute warm up before the recording starts, this one is from a dead cold start, so we show a longer and more dramatic warm-up ramp on the graph. The drive is the same route that most of the runs on the Denali were recorded at, so I'm very familiar with what could be happening and when, as far as speed/direction/sun load.

 

16FordMANUAL.png

 

Far as I know, the Ford has an active temperature reading during operation and adjusts accordingly. This would be very similar to my 2012 GMC, but not like the 14 and up GMs (or maybe just 16, I was told by the Tech that 14 made the change). 14 and up, GM does not actively check the temp in the vehicle (one reading at start and then no more) and does it all "on an algorithm" which is really what I see and feel happening.

 

The guys that say their truck is not quite right, one click seems to be too much in either direction - well, it is. The test gear shows there's usually closer to an 10F temp change by that one click on the dial. Frustrating.

 

So yesterday I fixed the HVAC issues, the passenger mirror turn signal that causes my wife to punch me in the arm when it flashes at night (it's so bright it's unbelievable), the Digital Steering Assist that eliminates power steering above 70MPH when TH is engaged, the cruise control that downshifts and engages the exhaust brake when you let off after passing a car and the seats that have two inset seams on the seat base that work to pinch the back of your thighs and butt when hitting bumps on the road...

 

The solution? I moved the driver from the vehicle on the left to the vehicle on the right (and left a big pile of $$ in between).

 

denaliTOplatinum.jpg

 

Not to say the Ford is perfect. I went with the GMC because my '12 was great and I presumed the 16 would be even better. There are lots of great things about the GMC, but if I can't be comfortable for long hauls, especially towing, then it's not a solution for me.

 

I suspect within a couple model years GM will figure out what they are doing wrong and get it sorted. I can honestly attribute the major complaints to the application of technology, specifically computer controls, in this truck. Software changes could resolve the HVAC, Digital Steering Assist and Cruise problems.

 

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