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Discussion Starter #1
Hi All,

New to the forum, and appreciate all of the help in advance. A few days ago I took my 2010 Sonata into the shop for routine maintenance (oil change and tire rotation). When my car was ready, they had it sitting out front with the valet key in it, turned to the on position. Interior lights were on, and headlights were on as well. I took the valet key out, and put my regular key in. Was just about to crank it with my regular key, and right when I hit the on position without it turning over to start, the car completely powered down. No lights (interior or exterior), no radio, no nothing.

I got out of the car, shut the driver's door, and hit the lock button on my original key fob. Lights worked, and interior lit up. Got back in the car, and the car started fine. But everything on the control panel had reset, radio reset, and the clock reset itself. Went right back in the shop since I was already there, and they said it was probably some form of security feature since I had switched the two keys out and tried to start the car immediately with the other key. I just had a new battery put in the car about 3 months ago, and hadn't had any trouble with weak starts or anything.

Now about three days later (no problems at all in this 3-day stretch between), I took about an hour drive on the interstate, left the car sitting for a few hours, came back to the car, and same thing. Got ready to start it and before it even cranked at all, everything went completely dead. No power anywhere at all, and this time the key fob wouldn't even work (like the way I did at the shop). Opened the hood, closed it, and key fob worked and car started fine. All the electronics reset this time as well.

Does anyone have any ideas what could be causing these random power failures? No weak starts, no dim lights, just random complete power failures, and even the key fob doesn't work sometimes now. Thanks for your time in advance!
 

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Thanks, for the advice! Just to give you an update, car had no power at all this morning. Key fob wouldn't even work. So I popped the hood and took a look at the battery. The connectors looked fine, but the small battery cover piece on the left-hand side of the battery looked elevated. I pressed it down, and the entire piece moved down a little bit. Immediately when it moved down, the car alarm went off. It looks like power has been restored for now. What are the two smaller connector pieces underneath the battery cover? They are located right next to the larger positive. I'm thinking whatever they are, pressing them down made everything work.

Thanks again for all of the help! This forum is a great resource.
 

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The part you pressed down on is (I'm pretty sure) the plastic cover for the battery terminal. It's mostly for show; it DOES NOT conduct any electricity from the battery to your car's electrical system. The terminal is metal, circular and wraps around the battery post; it's held in place with a 10mm (?) bolt. From what you said, you've got loose or corroded battery terminals; they may look fine but pushing down on the plastic and getting the reaction you got proves it. Remove your terminals, clean them inside and out and retighten.
 
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