2012 Hyundai Sonata – Intermittent Electrical Failure / No Start

[dja4260]

My father gifted me his 2012 Sonata. Last week it failed to start. The battery was from 2019, so I replaced it with a slightly lower CCA battery from Walmart. The car ran fine for a day or two.

While driving, all the dashboard lights started flashing and I lost electric power steering. When I tried to restart the car, the dash flashed, the horn beeped erratically, and it would not crank. I pulled into a parking lot and got a ride home.

The next day, the car started normally and I drove it home. I returned the Walmart battery and installed the correct Group 24R battery from Costco. I tested the battery and alternator with a multimeter and the alternator appears to be charging. I also checked and cleaned the battery grounds and verified solid connections.

This morning, the car started normally using remote start, but the doors would not unlock with the key fob. When I unlocked the door with the key, the dash lights immediately went crazy again and the horn started honking erratically.

Looking for ideas on what could cause these intermittent electrical issues. I'm going to pull the horn fuse, as my neighbors are beginning to hate me!

 

[fantastic]

Alternator? Check battery voltage before and after starting it to see if it's charging.

 

[twX]

This morning, the car started normally using remote start, but the doors would not unlock with the key fob. When I unlocked the door with the key, the dash lights immediately went crazy again and the horn started honking erratically.

Some cars will activate the security system and start honking the horn if the door was locked with the fob, but then opened manually with the key. If that's what was happening, you may have already solved the problem, which may have just been a poor battery connection.

Considering you had just replaced the battery, a problem with the battery or its connections seems most likely. That doesn't explain why the fob wouldn't work, but that may be unrelated, or because the computers were reset or something. Did the fob start working again?

 

[dja4260]

Some cars will activate the security system and start honking the horn if the door was locked with the fob, but then opened manually with the key. If that's what was happening, you may have already solved the problem, which may have just been a poor battery connection.

Considering you had just replaced the battery, a problem with the battery or its connections seems most likely. That doesn't explain why the fob wouldn't work, but that may be unrelated, or because the computers were reset or something. Did the fob start working again?

I haven't touched it. I went home sick, I think I have the flu...

 

[Nick1994]

Remote start on a 2012 Sonata? Is it an aftermarket kit?

 

[pvs2487]

My son had a similar issue with his 2011 Tuscan. Turned out to be a wonky positive battery clamp that didn't make good contact with the post even when fully tightened. I added a 'battery post shim'- looks like a thimble- which allowed for a more secure connection. By the way, the cable assembly is no longer available

Hope this helps.

 

[dja4260]

My son had a similar issue with his 2011 Tuscan. Turned out to be a wonky positive battery clamp that didn't make good contact with the post even when fully tightened. I added a 'battery post shim'- looks like a thimble- which allowed for a more secure connection. By the way, the cable assembly is no longer available

Hope this helps.

I'll need to give that terminal a good look over! Thank you for the insight.

 

[dja4260]

UPDATE. All terminals look good. I pulled the horn fuse so the neighbors don't kill me. Today, the alternator showed it wasn't producing any voltage, which makes sense if it's been intermittent with the issues that I've experienced. I have a local guy who rebuilds them. I just gotta yank the alternator out and drop it off.

 

[Drifter]

Glad you found the issue. Son drives a 2012 Sonata (that I maintain mostly lol) so this caught my eye. Hit us with a follow up. Best of luck to ya.