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On our 2012 Sonata the fuel gauge has started acting up within the last month or so, we noticed it one day, it said we were empty even though my wife had filled the tank earlier that day, when we went to get more gas it only took a couple of gallons. When it happened we thought it was just some sort of anomaly, but now its becoming more and more frequent. We have taken it to the dealer 2 times to have them take a look, both times they said they were not able to recreate the problem and charged us a diagnostic fee. She has taken quite a few videos of it happening, and even showed them the videos. Has anybody here had the same issue? Here is the youtube link to the video so you can see.

Thank you
 

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Try a few bottles of FI or fuel system cleaner.
Don't run it down to empty.
 

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To me it seems to be more of an electrical problem.
An electrical diagram or schematic would show all the affected parts and circuits.
Maybe have the dealership start with the fuel level sending unit??

Just a guess

Good luck
 

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Although it's impossible to tell for certain without being able to see and diagnose the car hands-on, this sounds like a typical failure of the sending unit which is part of the low pressure fuel pump in the tank. In this case the fix would be to replace the pump/sender assembly.
 

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2013 Hyundai Santa Fe Sport
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Doing mine soon for this exact problem. Some have reported that banging on the top of the tank will free a stuck one but the unit is dying.

BTW I believe copper top is experiencing the same issue. Hyundai is gonna be doing that one under warranty.
 

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2011 Sonata 2.0T, same problem. Started happening this summer in hot weather (maybe unrelated) around 56k. I would fill up, and then the next morning it would show a half tank or less, then jump around.

Brought to the dealer, they couldn't replicate the problem, charged a diagnostic fee. It hasn't happened the last two fill-ups, but weather is cooler so that's why I associate it with the heat. Again, that's probably unrelated, I don't know these things work.

What is the sending unit?
 

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It's an electromechanical device bolted to the in-tank fuel pump. There is a float attached to an arm which rides is attached to a sensor. I believe the resistance inside the sensor changes based on the position of the float arm. The car interprets the differing values as the bars on the gas gauge.

As the part fails the readings become increasing erratic until they cease and the car appears to be perpetually empty.

And it seems like it's gonna be a PITMFA to replace.
 

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Above is not a Hyundai part.... but, if you have any evaporated fuel gum, or moisture caused corrosion(old fuel ethanol humidity)..... sometimes it can be cleaned. Sometimes the float just hangs up. Other times the variable resistor just fails.

I've had multiple fuel senders over the years fixed with FI cleaners. I make the habit of never going below a 1/4 tank of gas. Ethanol, low fuel levels, and moisture are not your friends.

So, give it several bottles of various FI cleaners and fuel lubes, never run it low on gas, stick with toptier fuel, and stick with a busy gas station. If after a few bottles and the issue continues then:

http://www.hyundai-forums.com/attachments/yf-2011-sonata-i45/62483d1368128550-fuel-gauge-error-13-fl-003.pdf
 

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I have a 2003 Hyundai Elantra my fuel gauge just started fluctuating what could be my problem
Look at the picture above with the square picture(in red). That is a potentiometer(variable resister) where the fingers that go across it deteriorate over time. The fingers are very tiny/fine and go bad with use. Just buy a new unit and replace it.
 
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