2017 Sierra Denali rear window EXPLODED!!!

[STRMTRPR]

.. just in case you thought this was just a GM problem.. nope, appears to be a sliding window with defrost problem.. seems like a pretty common failure on F150 as well (maybe more common)..

 

http://www.carproblemzoo.com/ford/f-150/rear-window-defogger-problems.php

 

...WOW nearly 130 documented F150 cases here

https://www.glassbytes.com/2013/12/several-ford-f-150-owners-report-shattering-back-lites-to-nhtsa/

 

.. link to file complaints for Canadian owners

https://wwwapps.tc.gc.ca/Saf-Sec-Sur/7/PCDB-BDPP/fc-cp.aspx?lang=eng

 

.. also found this interesting GM bulletin..

https://gm.oemdtc.com/1974/14815-heated-back-window-glass-structurally-weakened-due-to-surface-flaw-2015-chevrolet-silverado-gmc-sierra

Edited March 16, 2019 by STRMTRPR
added link

[2018GMC]

Pulled the square 30A # 10 fuse from the under hood fuse box. 

 

The rear defroster button still lights up on remote start but rear window is cold ?  to touch. ?

Edited March 15, 2019 by 2009GMC

[Blue5.3l]

37 minutes ago, 2009GMC said:

Pulled the square 30A # 10 fuse from the under hood fuse box. 

 

The rear defroster button still lights up on remote start but rear window is cold ?  to touch. ?

I’ve been think of pulling the fuse or relay also. Do the heated mirrors still work when the button is pushed?

[STRMTRPR]

yes the heated mirrors still work.. they are on their own fuse

[STRMTRPR]

.. so I was thinking about this window problem as a short resulting in an increase in current flow..and the possibility of introducing some form of current limiting/monitoring to prevent overheating/melting/smoking

..BUT.. I haven't seen any reports of the fuse blowing - this is at its simplest the weak link in the circuit and basic overcurrent protection.. so why didn't it blow? let's assume the current flow never reached the 30A threshold at the time of failure.. what is the current draw under normal operation? I measured the current flow of my rear defog circuit today; and for the purpose of simplifying the hypothesis here it I'll round it off to: 18A at cold startup of 0C or 32F. Let's also assume that the circuit voltage is always constant.

..so if we are correct that the current draw never reached the peak 30A rating of the fuse where did all the heat/smoke come from? .. now this is going way back to my days in school but it then only makes sense that condition responsible is resistive heating (l2R).. increased resistance from poor contact of the middle sliding window.. think toaster oven, space heater etc.. this phenomenon causes thermal expansion and can literally melt wires.

 

.. Circuit design theory is not my area of expertise.. my background is Robotics.. so I'm hoping for members with expertise to chime in with thoughts.

 

.. If the window is indeed experiencing resistive heating from a high resistance connection due to poor/short sighted design what can be done as a preventive failsafe?.. add a cycling thermostat or thermal fuse like used in a clothes dryer?.. would be a rather ugly preventive measure to what is likely a design flaw with the window connection.. and seems unlikely that GM would step up and go the design route given what also seems to be a known problem with the Ford window design (same glass supplier??)

 

 

Edited March 17, 2019 by STRMTRPR
.. thoughts on dryer fuse

[2018GMC]

On 3/15/2019 at 5:19 PM, Blue5.3l said:

I’ve been think of pulling the fuse or relay also. Do the heated mirrors still work when the button is pushed?

Yes I verified this morning that my mirrors were warm and my rear window was cold since I pulled the fuse.

[NCPGMC]

On 3/15/2019 at 8:19 PM, Blue5.3l said:

I’ve been think of pulling the fuse or relay also. Do the heated mirrors still work when the button is pushed?

Yes, just pull the fuse only. The relay controls both the mirrors and the rear defogger. 

[1SLOW1500]

.. so I was thinking about this window problem as a short resulting in an increase in current flow..and the possibility of introducing some form of current limiting/monitoring to prevent overheating/melting/smoking
..BUT.. I haven't seen any reports of the fuse blowing - this is at its simplest the weak link in the circuit and basic overcurrent protection.. so why didn't it blow? let's assume the current flow never reached the 30A threshold at the time of failure.. what is the current draw under normal operation? I measured the current flow of my rear defog circuit today; and for the purpose of simplifying the hypothesis here it I'll round it off to: 18A at cold startup of 0C or 32F. Let's also assume that the circuit voltage is always constant.
..so if we are correct that the current draw never reached the peak 30A rating of the fuse where did all the heat/smoke come from? .. now this is going way back to my days in school but it then only makes sense that condition responsible is resistive heating (l2R).. increased resistance from poor contact of the middle sliding window.. think toaster oven, space heater etc.. this phenomenon causes thermal expansion and can literally melt wires.
 
.. Circuit design theory is not my area of expertise.. my background is Robotics.. so I'm hoping for members with expertise to chime in with thoughts.
 
.. If the window is indeed experiencing resistive heating from a high resistance connection due to poor/short sighted design what can be done as a preventive failsafe?.. add a cycling thermostat or thermal fuse like used in a clothes dryer?.. would be a rather ugly preventive measure to what is likely a design flaw with the window connection.. and seems unlikely that GM would step up and go the design route given what also seems to be a known problem with the Ford window design (same glass supplier??)
 
 

This kid is on to something. Many key works in there are spot on.
When and where the load is the highest is where you will have the hottest spot. And where the failure will occur. What can be done to reduce this and when what is the best amp rating of the circuit? Like all things the draw can be high then reduced after a second or so, think hid lights running super low amps but to start we have seen a need for up to 30amp fuses. So the difficulty is how do you protect that circuit.

Sent from my SM-N960U using Tapatalk

[Harold Harkonen]

I finally got my window repaired by the dealer at no cost.  They claimed GM had not found the cause of the wiring fire and window shattering but had another truck with the same issue where the window didn't break and they have sent the window away for analysis. Being a curious electrical engineer I believe the problem could be either a sticking defogger relay that I assume is supposed to cycle the current to the defogger, or a programming glitch in the computer that controls the relay. I tested the relay on the bench but it did not stick with multiple operations. I have disabled the automatic window defog on remote start (since I think that is a possible source for a programming problem). Hopefully GM figures it out soon and refunds the money that people have paid out to fix the damage on their own.!

[Szilla]

On 3/20/2019 at 9:13 AM, 1SLOW1500 said:

This kid is on to something. Many key works in there are spot on.
When and where the load is the highest is where you will have the hottest spot. And where the failure will occur. What can be done to reduce this and when what is the best amp rating of the circuit? Like all things the draw can be high then reduced after a second or so, think hid lights running super low amps but to start we have seen a need for up to 30amp fuses. So the difficulty is how do you protect that circuit.

Sent from my SM-N960U using Tapatalk
 

You obviously know a solution, but won't post it.  Can you message or email it to someone?  You don't have to include technical GM bulletin info, just "install smaller fuse" or "electrical grease on contacts" or similar will work.  

[Harold Harkonen]

On ‎3‎/‎26‎/‎2019 at 11:51 AM, Szilla said:

You obviously know a solution, but won't post it.  Can you message or email it to someone?  You don't have to include technical GM bulletin info, just "install smaller fuse" or "electrical grease on contacts" or similar will work.  

My opinion is that it is a programming glitch that keeps the relay on too long in certain situations, can't protect against that with a fuse. GM would have to fix that and issue a recall. A poor design in my opinion when a fuse can't be applied properly to prevent a fire.... 

[1SLOW1500]

My opinion is that it is a programming glitch that keeps the relay on too long in certain situations, can't protect against that with a fuse. GM would have to fix that and issue a recall. A poor design in my opinion when a fuse can't be applied properly to prevent a fire.... 

Fuse cant help and the same circuit runs the mirror heaters. And saying it keeps it on too long in certain situations means the bcm would have to read another senor be it a temp or baro. Dont see that major software or hardware update being made.
Keep the window contact clean and electric grease then keep your eye on it.
There are other things you can do but on this forum everyone is going to scream for gm to do it. When they don't they will just post something should have been done. And true but I see it as a waste for most people here.

Sent from my SM-N960U using Tapatalk

[Harold Harkonen]

3 minutes ago, 1SLOW1500 said:

Fuse cant help and the same circuit runs the mirror heaters. And saying it keeps it on too long in certain situations means the bcm would have to read another senor be it a temp or baro. Dont see that major software or hardware update being made.
Keep the window contact clean and electric grease then keep your eye on it.
There are other things you can do but on this forum everyone is going to scream for gm to do it. When they don't they will just post something should have been done. And true but I see it as a waste for most people here.

Sent from my SM-N960U using Tapatalk
 

2015 Cadillacs were recalled for the same thing but of course all they did was disable the auto defrost mode. I am sure the relay doesn't cycle based on a sensor but it just set to a timer. Greasing a connection inside the truck isn't going to do much, there is no extra corrosion there to make a hot spot worse. The connection obviously isn't designed properly for the service. The more people complain to GM and NHTSA then the more likelihood something will get done before a baby in a rear car seat is hurt or killed by this defect. Not a waste for most people searching for this problem. Manufacturers need to fix their design defects not worry about goddamn lawyers and insurance. They will just keep ignoring if people don't know where to complain.

[Harold Harkonen]

Another design issue that I see is that GM is trying to protect 3 separate defroster grids on the sliding rear window with one fuse and wire connection to the fuse panel instead of using 3 separate wires with smaller fuses. Might have been a cost cutting measure but violates a basic design rule in my opinion.

[MarkMacie]

Just happened to my truck this morning.  GM services entered my info and said they cannot do anything to help unless there is a bulletin on the problem.  They told me I am at the mercy of the Dealer, dealer fees, and the dealers service manager.  Very disappointing.  I've told everyone I know that owns a newer Silverado to NOT use the rear defrost!!