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Need help pinpointing an electronic problem

I drive a 2010 Sonata with about 73,000 miles. Suddenly multiple electronic systems are not working:

  1. Remote key fob (battery is good) does not operate door locks, or trunk release, or panic button alarm.

  2. Interior trunk release will not work unless the key is in the ignition switch. Interior door lock switch does the same (works, but only if the key is in the ignition). Normally, these both function without having to have the key in the ignition.

  3. Programmed rear view mirror will not open garage door. Other electronic rear mirror sensors seem to work. It shows the LED compass direction, for instance.

  4. Digital clock does not show time.

  5. Interior dome light does not come on with door open, nor manually. Map lights will not turn on. These bulbs were all fine yesterday.

  6. Dashboard shows the TPMS light problem indicator, but it has never been lit before. No reason to suspect a problem here.

  7. All these features stopped working simulaneously; none has ever been a problem before. This is my fourth Hyundai Sonata, btw, and I’ve never had electrical problems before (very few problems at all, in fact).

  8. Other electrical systems are still functioning. For example, the radio, power windows & seats, wipers, A/C, exterior lights and instrument controls on dashboard all work fine. Electric sunroof, electric side mirrors, electric seat motors, blinkers and headlights work fine. Car drives normally.

Since so many diverse functions failed simultaneously, I expect a failed electrical control module/elctrical relay rather than a fuse – in any case, I can’t imagine why the digital clock and door locks and trunk release and TPMS systems would all be on the same circuit together.

Anyone have this problem before, or any bright D-I-Y suggestions about pinning down the failed component that would affect all these things at once?

Check the fuse in the passenger compartment labeled “Memory Fuse”, it powers the Body Control Module and the interior lights.

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Yes, it looks like that is where the problem is - Thanks! I tried replacing the 15 amp fuse twice, but it shorted out two more the second I tried to re-insert.

Would that indicate a short somewhere specific, do you think?

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The short is likely to be in the interior lighting circuit. Start with the vanity lights located in the visors, the wiring in the sun visors might be chafed and shorted. Remove both visors and try another fuse.

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That sounds like a great idea – thank you very much!

Hey DLewis…I have realized I just had the same problem with my Sonata all those lights and problems randomly/simultaneously came on. Its been driving me crazy.

Was Wondering if you have ever found a solution to this? Please reply back ASAP.

Thank you.

Is the same Memory fuse blown out that the previous poster had trouble with? If so then check the wiring to the visor lights. Power is tied to them at all times. One thing you can do to help solve the problem is install a tail light in place of the fuse that blows out. It will act as a load and limit the current to the short. When the short is removed the light will go out.

Another thing that can be done is use a ohmmeter to monitor the protected side of the fuse position. While the short is on the line the resistance to ground at the fuse will be very low. When the short is removed the resistance will go up significantly. Indicating the short is gone and safe toput a fuse back in place.

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First off thanks for the reply, I appreciate it.

Yes, Yesterday i realized it was the memory fuse; the 10a one to be exact that keeps blowing. So i got it replaced and everything worked perfectly! All the lights (tire pressure, trunk, dome, key fob etc.).
Then last night I turned on the dome light (which only one works now) and then i heard the fuse pop again! Very frustrating but i ended up putting another 10a fuse again and since then i have turned off the dome lights and everything has been working.

However, I am not a mechanic but i do want this to be fixed where i wont have to worry anymore. I just don’t understand how Hyundai has all these lights connected to one another.

More, importantly is there a simple way For me to fix it or figure out where this shortage is coming from (I am assuming its the front dome lights and not the the visor lights. But obviously, if you have any simple ways for me to do it myself or a way for me to look at it and give a hand to my mechanic??

Thank you.

By the way the visor lights have an on and off switch which i have always had off.

Also what is a tail light??

From what you say about the problem it appears to be intermittent. These kind of problems are hard to find since they are not there most of the time. Even though the visors have power switches I assume you can turn the visor lights on while the ignition is off. This means power is still available to the visor switch, and a short on the line before the switch will blow the fuse. Sometimes wires get pinched between a screw and chassis ground. It is very helpful to have a circuit diagram that shows all the areas the fuse supplies power to so you can check those areas. You start with the most likely spots for trouble first.

There are tracker systems available that help find shorts like this on the line.

A tail light is the bulb used in the back of the car for the running lights. They use about 12 watts of power to run. By putting the bulb in a socket and wiring the socket to a blown fuse body the light will act in place of the fuse. The shorted circuit will only be able to draw enough current to run the light since the light is in series with the power to the short. When the short is removed the light will go out since no current can flow when the short is removed, unless there is some other normal load drawing a small amount of current.

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That makes much more sense. I will definitely try these options by tomorrow, if not sunday and get back to you on that. I really do appreciate your time & effort to explain that to me. Thanks again.

You’re welcome for the help. If you make up a tail light test jig and the short is on the line when you put it in place the light will be at full brightness due to a direct connection to ground via the shorted line to ground. Once the short is gone the light will go out IF there is nothing else drawing current. You just need to be aware that the light still may glow some if something else is drawing current, which is normal.

You would be wise in getting a factory wiring manual for the car if you are going to work on this yourself. It will be a very good investment and save you a lot of time in finding things. The fuse most likely powers a number of other things besides the visor lights and the short can be on any one of the power leads. Ebay is a place to get factory manuals.

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Amazing!! Clarified it to the fullest! That’s literally what i was looking at. But yes, now that you made it clear with the currents and lightning, i will be aware of that. However, I will be working on this with my personal mechanic so I will have an extra hand. But in due time I am going to get the factory wiring manual/diagram to do this job properly. Especially that your right about the fact that specific fuse does power many other things so I dont want to wing it…and if you have any other advice/tips dont hesitate to throw it out there.

Will definitely keep you updated on this one.

Thank you!!!

If the short isn’t happening while you are testing it help to tap on suspected trouble areas using a screwdriver handle or something similar to help show up the trouble and watching for a change to the light.

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Awesome!! Got it!