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Discussion Starter · #1 ·
2011 Sonata Ltd, 65,000miles, keyless

Was doing some cleaning on the car last night and was washing the windows and putting on some rain-x. I pushed the start once to get the accessories working and listened to the radio while I worked for about 30 minutes. It was dark and I keep my lights on "auto" so thay were probably on as well.

When I was done, I pressed the start button twice more to shut it down. The headlights and interior lights stayed on but I assumed that they woudl shut themselves off when I locked the car. After 5-10 minutes, the lights were still on. I got in the car and tried to start it but it would not start. Not even trying to turn over. Then all **** broke loose and everythign starting flashing. The headlights flashed, the parking lights flashed. The dash flashed. The flashing was not timed like a blinker but rather frantic like it was shorting out. I could not get it to stop regardless of what I pushed (keyfob, start button) so I disconnected the negative battery terminal.

I let the car sit for 5-10 minutes and then reconnected the battery. The car reacted as if the battery were dead. The remote would not work, I was locked out of the car and had to use the physical key to open it. The car would not start or even turn over. I put it on a charger for 30 minutes and it started after that and ran fine.

I suspect that the battery may have been weak going into this so perhaps the freaky behavior was due to low power. I will have the battery checked later this week.

I am looking for anyone that has seen this before and how their story ended. Also, does anyone know what warranty is there on the original battery? Go to dealer or my trusted mechanic?

All suggestions are welcome.
 

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The stock battery is 2 years full replacement or 3 years pro rated I think. Double check with your dealer. Im not sure what battery your car comes with but the capacity of mine seems awfully weak for the car. I plan to replace mine with a stronger interstate battery when it craps out.


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Thats an odd behaviour. . Cars usually dont go crazy when there is low voltage. The electrical system os regulated by capacitors, transistors, relays and etc. They would require an X amount of voltage to turn on and if there is not enough voltage, it would stay off. Well I can attest to this on mazda 3 and suzuki vitara. Perhaps hyundai designed this car a little different.
 

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If you car is under warranty (5/60K btb), I would have it checked at the dealership. You may or may not have a failing body control module.

Trix is correct---there was not enough power to drain your battery to dead (I usually play my radio while detailing for 4 -5 hours and never had anything like this) I also am on my stock battery and its still going strong.
 

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If you car is under warranty (5/60K btb), I would have it checked at the dealership. You may or may not have a failing body control module.

Trix is correct---there was not enough power to drain your battery to dead (I usually play my radio while detailing for 4 -5 hours and never had anything like this) I also am on my stock battery and its still going strong.
He's out of warranty [65k].
 

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Discussion Starter · #6 ·
For what its worth. I was able to reproduce the problem last night so I feel good about taking it in. I hate having something intermittent and not knowing if it will happen when the tech checks it. I'll update when I get a diagnosis.
 

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when you reproduced the problem, were you able to turn off the car by pressing the push button start for 2 seconds? If the car doesn't shut off, there may be a bigger issue that could mean sonatas being recalled. Cars with push button ignitions HAVE to have a working kill switch.
 

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Discussion Starter · #8 ·
My trusted mechanics diagnosed a dying battery. he also said not to leave the headlights set to "auto" when running on battery only. seems to me that a 2011 model ought to be able to shut itself down before the battery level becomes critical. Also, not sure why the headlights on "auto" shold be able to turn on when the engine is not running.

Trixstar: The engine was never running so it was only the electrical system that was operating. I did hold the start button down for more than 2 sec and it did not shut down.

Not really looking to test it again with the new battery.
 
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