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So I'm driving to work this morning I press the rear defrost button for the first time this year, and my radio went dead. I don't mean that it just shut off, I mean no lights on the display and the overhead OnStar panel went out. Not only that but the defroster light came on but the defroster did not work. Relay does not click, and no voltage at the rear window connectors. All fuses and relays are all good. All electrical connections are solid. The only electrical changes to my car since the last time I used the rear defroster was the installation of the GM fog light kit, and the dealer flashed the BCM to turn fog light function on. Its my understanding from the limited information available that the Defroster Is controlled by the BCM, and obviously the Radio is connected to it as well, since the vehicle options are displayed on it. Is it possible something went wrong with the flash? Dealer won't even look at it for less than $125.

Edited by NDAMT
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Appointment tomorrow to have them look into it. Will update.

 

OK, turns out that the BCM calibration file that was installed to allow my LS to use the GM fog lights screws with the Battery Saver relay settings. For whatever reason, when the defroster button is pressed, it not only trips the defroster relay, but also the battery saver relay, turning the radio off, and effectively frying the relay. Service manager says that the Chevy Tech Support person he was talking to immediately knew what was happening and what the cause was, but at the same time they didn't want to admit that there was a problem with the original calibration download to the BCM.

 

Long story short, next week I should be getting a new Battery Saver relay and a NEW new BCM calibration that will allow me to use both my fog lights, AND my rear defroster & radio. In a perfect world, I wouldn't even have to pay for any of this.

Edited by NDAMT
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  • 2 weeks later...

I have never had any benefit from fog lights..we get alot of fog down here and the one car i did have fogs on would just illuminate the fog making it harder to see...never used them since..that was back in '92 BMW. Mind you, they were very useful for scaring Frogs off the road at the numerous Frog crossings on the Everglades pkwy.

Edited by Retired old Gearhead
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OK, as of 10/14 finally fixed.

 

Dealer downloaded the data from BCM and uploaded it to GM. GM de-compiled the program and found an error in it. Apparently the rear defroster and the Battery Saver relay utilize the same timer and since the rear defroster shuts off automatically when the car is turned off, they should never both be active at the same time. The error in the program tripped the battery saver circuit when the defroster button was pushed, and since both would be active in that instance, it blew out the relay, effectively killing the radio/onstar/turn signal & warning sound, etc. and the rear defroster.

 

GM made the changes to the program and Dealer downloaded to BCM. No more problems as of yet. Most bizarre issue I've encountered to date.

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  • 2 months later...

Hi NDAMT,

 

I am now having the exact same problem with our 2014 1LT. We had fog lamps installed, now the rear defrost button kills the logic/battery saver relay. We found this post before taking it back to the dealer, but the dealer was unwilling to even look at this post. He felt that if he just replaced the relay we would be good- at our expense of course.

 

The next day as we were headed out of town and I decided to push the rear defrost to see if the problem was truly fixed- which promptly killed the radio, on-star services, and all safety chimes. We have called GM and have voucher to take it to another dealer.

 

Did GM make it right financially for you? 

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Update on our issue. We called the dealer who had installed the fog lamps, and the subsequent logic/battery saver relay on the 23rd of December to let them know the problem was not resolved. We left a message for the service manager who we were working with, but they never called back. 

 

We got GM involved and they had us take the car to another dealer for a second opinion. This dealer informed us that the BCM is bad, possibly because of low voltage during the fog lamp install. GM does not believe that ours is a software issue. Now we have to take it back to the dealer who installed the og lamps and start a dispute :(

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  • 3 months later...

Moral of the story is...avoid any dealer installed electrical related modifications? If it is not factory installed, the dealer mechanics have no background in electrical engineering and things can go haywire.  If you want some electrical accessory, order it with the new car, if offered as an option. 

Only dealer modifications I trust is mechanical gadgets like mud flaps, body side moldings, metal add-on's to gas pedal & brake pedal, all weather mats, bumper guards, add on rain gutters on roof etc.

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Been meaning to get back here and do an update. GM sent us to another dealer, who determined that the BCM was bad and wanted us to have it replaced. Then, a few days later, the dealer who had installed the fog lamps called us and, lo and behold, had been informed by GM that there was an error in the software and the BCM needed to be re-flashed with corrected software. We were reimbursed for the battery saver relay, but the dealer was entirely apologetic, and we never again heard from the GM rep who was dealing with us, even after leaving a voicemail on her extension. So GM caused us a major headache during the holidays, jerked us around, and never bothered to apologize for our loss of time. Moral of the story is...this will be the last GM car we buy.

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