02 hyundai sonata charging trouble

Got this car for my daughter 4 months ago and it has not been driven since. When we bought it they told us the alternator was bad so they replaced the alternator for us. Got the car home okay but the radio would turn itself on and off it’s a factory radio no extra doodads. I did notice the valve cover gasket was leaking really bad and the vehicle was living in the country on a dirt road so it had 1/2" mud sludge from spark to drain. So I bought a bottle of super de-greaser and a hose and scrubbed the motor down. (Got water in the plugs) drove on 3 cylinders to midas and had them replace valve cover gasket new plugs and wires oil and check for anything else needed.
Present day.
Took car to oriley’s, auto zone, & advanced auto and had charging system checked. All 3 say bad voltage regulator. Pulled alternator took both alternators (I had the one the seller replaced also) back to the 3 stores for Bench test and both passed 3 times.
Put the new one back in the car and sho nuff…bad voltage reg.
Thought it would be from the bath I gave it but considering the seller replaced a good one for another good one… I have to figure out why it reads bad voltage reg. 02 hyundai sonata 4cyl
Thanks for reading my novel hope someone can help

You have a few things here, including fuses and fusible links that could be bad.

Ok thanks for the reply. I will start checking and let you know what I find

Oh yeah I forgot. Had codes checked and cleared but the one that pops up is something to do with vacuum line/gas cap not on

What is the voltage reading at the battery clamps while the engine is running? Need to know this

That 120Amp Fuse would NOT be the culprit… you would have zero voltage at the batt while running the engine… Not sure what that fuse in the fuse panel inside the vehicle does tho…

Typically there is NO FUSE that can affect the voltage regulator in the Alternator…or anywhere else for that matter. If a Voltage Regulator dies…it does so silently with no way to have any control over it via any kind of fuse…


I still have the factory diagrams for my previous car, an 02 Sonata.

Turn the key on but don’t start it. Does the charge idiot light come on? If not check interior fuse 18, it’s a 10 amp

Under the hood check the “ECM fuse” it’s also a 10 amp.

Flip the fuse box lid over to see the fuse listings.

I get 14v when only engine is running but when I turn on lights and a/c it slowly drops down to 10v
87 ranger,
I had high hopes with your reply but every fuse is good. No charge idiot light

The ecm controls the voltage reg right??
Could it be bad and how would I check it?
The battery light was on when we test drove and hasn’t come on since (except whe we broke a belt two days after purchase) but isn’t on now.

The 10A ECM fuse for sensing is good? That leave the PCM or wiring? The PCM controls the charging. All wiring and connections have to be tight and clean. They also need to make it from point A to point B. If it’s dropping under load then the sense circuit not working.

14V is about right when the engine is running… Sometimes the battery is the culprit in these circumstances. If you have 14VDC while running the Alternator is doing its job…The batt may have a few dead cells inside of it, happens all the time really. The reason you get 10VDC while the lights are on is because the alternator voltage regulator is working and the lights subtract voltage from what the Alt can provide… The battery is responsible for providing proper voltage to accessories and the alternator will fill the batt back up.

Think of the battery like a Well of water… What is happening here is that your well is being filled up with sand… The more sand(Dead Batt Cells) the less water it can provide… The Alternator is like a steady stream of water attempting to refill the well with water. The stream is flowing…but the well is unable to hold the water…because it is too full with sand.

I would suspect the battery in your instance… See if you can borrow a known working and good battery for a quick test… it doesnt even need to be the correct size or anything… Just for test purposes. You may find that everything is back to normal with a known good batt.


Thanks for all the replies.
So here’s an update. (Battery is good) stereo keeps resetting itself and I go from 14v to 12.2v with the blower fan on high

Make sure you have good, solid grounds for both the alternator and battery to the chassis. If one of those grounds works loose, or corrodes, it can produce a symptom that appears like a faulty voltage regulator.