Can Rear Defrost (Defogger) be set to continuous (DIY solution)?

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'12 Mazda5 GT
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‘17 CX-5 GT
Is it possible to change the factory setting of the rear defrost from "15 minutes" to "Continuous" without going to a Dealer? For reasons unknown this is a personalisation setting that exists, but can only be performed at a dealer. Is there a button press combination that will get me into the secret menu to change this? Excerpts from the Owners Manual showing the option does exist. For the type of driving I do "Continuous" would be far more useful, mostly for the fact it would keep the heated front wiper defroster on continuously in snowy/icy weather. (2017 CX-5 GT Canadian)
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2019 CX5 Reserve AWD
Dont think so. The reason for the 15 minutes is when they first started putting defrosters on the rear window the heat from continuous operation would cause the window to crack so they came up with 15 minutes. Been that way ever since.
 
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'12 Mazda5 GT
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‘17 CX-5 GT
I think that may have been a reason, "back in the day" but I think that issue has been solved, otherwise it wouldn't be an option at all. Seems odd the dealer can do it, but not an owner. Because even if they warned you about the rear window cracking and confirming you really really wanted to do it anyway, that it would absolve Mazda or Dealer of liability.

I find it mildly irritating that the front wiper defrost is linked to the rear defrost. On a highway road trip in winter there are often times I want the front wiper defrost to stay on indefinitely. However, in such times, I prefer to have the rear defrost off. that way, during inclement weather, the rear window stays stays wet and the wiper is more effective. Having the rear defrost on dries the rear window, thus significantly reducing the effectiveness of the rear wiper. Unless of course you burn through a gallon or two of washer fluid on a 2-hour road trip.
 

madar

Contributor
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2016.5 CX 5 Touring AWD, 2015 SCION XB
Dont think so. The reason for the 15 minutes is when they first started putting defrosters on the rear window the heat from continuous operation would cause the window to crack so they came up with 15 minutes. Been that way ever since.
Didn't know that, I always thought it was to reduce drain on the battery...
 

yrwei52

2016 Mazda CX-5 GT AWD w/Tech Pkg
Contributor
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Plano, Texas, USA
Is it possible to change the factory setting of the rear defrost from "15 minutes" to "Continuous" without going to a Dealer? For reasons unknown this is a personalisation setting that exists, but can only be performed at a dealer. Is there a button press combination that will get me into the secret menu to change this? Excerpts from the Owners Manual showing the option does exist. For the type of driving I do "Continuous" would be far more useful, mostly for the fact it would keep the heated front wiper defroster on continuously in snowy/icy weather. (2017 CX-5 GT Canadian)
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If the manual says changing the rear window defogger setup can only be done by the dealer’s Mazda MDS computer, that should be it. You can either know this in advance and ask the Mazda dealer to change the desired setups for free during the car purchase, or you may have to pay the change afterwards.

Until someone developed an software to access Mazda’s MDS system like the VAG-COM VCDS developed by RossTech for VW / Audi which is the Interface to log into car's ECU diagnostics computer and do all the setup changes, not much we can do for these dealer-only setup changes.
 

yrwei52

2016 Mazda CX-5 GT AWD w/Tech Pkg
Contributor
:
Plano, Texas, USA
I think that may have been a reason, "back in the day" but I think that issue has been solved, otherwise it wouldn't be an option at all. Seems odd the dealer can do it, but not an owner. Because even if they warned you about the rear window cracking and confirming you really really wanted to do it anyway, that it would absolve Mazda or Dealer of liability.

I find it mildly irritating that the front wiper defrost is linked to the rear defrost. On a highway road trip in winter there are often times I want the front wiper defrost to stay on indefinitely. However, in such times, I prefer to have the rear defrost off. that way, during inclement weather, the rear window stays stays wet and the wiper is more effective. Having the rear defrost on dries the rear window, thus significantly reducing the effectiveness of the rear wiper. Unless of course you burn through a gallon or two of washer fluid on a 2-hour road trip.
The choice of changing the vehicle feature setups either by the owner or by the dealer IMO is decided by the car manufactures unless the features are limited by the regulations. For example I can easily change the DRL setup from vehicle setup page from the same infotainment screen on my 2018 Toyota Yaris iA which is the Mazda2 in disguise, but I can’t find the same DRL setup change on my CX-5. Toyota has always been giving the owners the choice changing the DRL setup easily mostly from the headlight switch. I believe Toyota also asked Mazda to make DRL setup change readily available to owners on the Yaris iA, hence Mazda modified the software interface on infotainment system for Toyota.

As for separate controls on windshield de-icer and rear window defogger, everything went down to the cost. Adding an extra switch and wiring for windshield de-icer won’t be cost effective for a few car owners like you who care about this.
 
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2019 CX5 Reserve AWD
Yes, that’s what I always thought too.
If you notice the heating element is molded inside the glass as opposed to just blowing hot air out of a vent. Blowing air would not be a problem but then you run into the problem of keeping the air hot enough as it makes the trip from the front to the rear.
 

yrwei52

2016 Mazda CX-5 GT AWD w/Tech Pkg
Contributor
:
Plano, Texas, USA
If you notice the heating element is molded inside the glass as opposed to just blowing hot air out of a vent. Blowing air would not be a problem but then you run into the problem of keeping the air hot enough as it makes the trip from the front to the rear.
The heating element on the rear window, unlike the windshield which is laminated, is only “attached” to the inside of the glass surface as it isn’t laminated.