2012 sonata engine problem

Was driving to work and my car shut off on me. It had only been running for a minute. I made it one block from my house. Tried to cut it back on and it just made the stutter cranking noise. After a while it stopped stuttering and power went dead. No lights or radio. Towed it to a shop and they said they tested the battery and alternator. They said it was not either and I should take it to a Hyundai dealer to get a better idea. The closest appointment at a dealer is a month out. I had it towed to a local mechanic and he’s saying the engine locked up and I need a new one and the starter went bad also from when I was trying to crank it. My question is does this sound right? Would my power go out if the engine is locked up? I ask because after searching the problem online some say it could be the fuel pump. I don’t want to buy a whole new engine and that’s not the problem. My car had gas and oil in it at the time of the problem. The milage is 117k. As I’m looking for a new engine I see that many used engines have much more miles on them. Is it even worth it to replace the engine at this point? I’m looking at about a 4 thousand dollar repair. How much more use could a new engine get?

These engines have an extended warranty on them for this exact issue. There is a good chance you will get a free engine from the dealer, they may even have free loaner cars as part of the extension. Do not install a used engine. It will likely have the same problem that yours does. Google Theta engine issues and you will get more details.


Did any red or yellow lights appear on the dash just before the engine shut off? Yellow is not good, red is really bad…

I’d say the mechanics you towed the car to were really poor ones to not be able to determine if the engine was locked up or not. You local mechanic seems better. If that shop tried to turn the engine manually with a wrench and it didn’t… you need a new engine.

Collect ALL the receipts and notes you have for oil changes. The engine is out of warranty since it is over 100K miles and Hyundai will use the lack of records as an excuse to deny the claim. They KNOW this is a problem and a used engine WILL have lock-up at about the same mileage.


No worries. If you have oil change receipts.

It would be nice if the people doing the diagnostics provided more definitive explanations or maybe they did and something got lost in the translation?

Yes, if the engine locked up and you continued to try starting it, the starter motor is stalled and drawing a lot of current which could blow the master fuse. Then everything would be dead but the battery could still have enough charge to appear OK when examined separately.

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Yes, you have a seized Theta II engine. Hopefully you have oil change receipts. They used to require the knock sensor update to give you a new engine but seems like they are doing away with that. Make sure the engine has enough oil when you tow it to the dealer. We had ours changed at 140+ miles for free. But I was aware of this issue and since our was burning oil since 60K miles, I had kept all oil change receipts going back to the day I bought it as a CPO with 20K miles. I do most of my own oil changes myself. They accepted my excel spreadsheet with the scanned copy on the oil/filter receipts.


What causes this? Common ways an engine can seize by my experience is

  • no engine oil
  • no coolant
  • water ingested into engine air intake (hydro -lock)

OP says engine had oil, and no mention of overheating, so only thing left appears to be hydro-lock.

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Poor quality manufacturing process of the engine/oiling system and or bearings failure can cause an engine to lock up ie seized rod bearing…

The cause is a faulty process when this engine was manufactured. When the engine was machined, the metal chips and debris is to be removed from engine. The chips and debris could not be removed properly from these engines. That is the conclusion I got 3 years ago when I was researching new cars.

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This is Hyundai Corporate’s official narrative, but it doesn’t really pass the smell test. If there was debris left inside the engine, such as metal shavings from the machining process, one of two things would happen: either the debris would end up in the oil filter or sink to the bottom of the oil pan, and be eliminated during normal maintenance, or it would end up lodged inside a camshaft/crankshaft/connecting rod bearing, resulting in failure within a few thousand miles.

It is simply not believable to suggest that debris from the manufacturing process can sit in an engine for years and many tens of thousands of miles, and then result in bearing failure at around the 60,000 to 100,000 mile mark. It is much more probable that something inside this engine comes apart due to inferior materials or design, generating metal shavings as the engine runs. The $10,000 question is, of course, whether or not Hyundai redesigned the short block given that they won’t even admit the actual cause of the problem.

Especially after all those oil changes…

Would the dealer be able to tell the difference between a hydrolock and the engine being faulty from the recall?

I expect most any experienced mechanic would be able to diagnose a hydrolock-caused engine failure pretty easily, but not necessarily quickly.

Pull the spark plugs and look for liquid in a cylinder(s), you basically can not compress a liquid and it will normally bend a connecting rod in the process… It’s not hard to see how the engine locked up, knowing why the engine locked up is the harder part…

Normally doesn’t take to long…

Hydrolock occurs when a volume of liquid greater than the volume of the cylinder at its minimum (end of the piston’s stroke) enters the cylinder . Since liquids are nearly incompressible the piston cannot complete its travel; either the engine must stop rotating or a mechanical failure must occur.

It happens a lot with the stupid cold air kits that are installed and the filter is low to the ground or in the fender well area, go through standing water and the water gets sucked up into the filter and then into the engine…

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I don’t think failure mode on these motors is headgasket. It’s a mechanical sort of crumbling. Metallurgy I think

As mentioned, the reason for the failure is just poor quality material. These engines start burning oil and it gradually gets worse until they fail. The metal shavings story was what they fed the media in the beginning but since then they have manufactured a lot of cars (including Kia’s) with the same engine and the same outcome. Only a few owners have been lucky. The fact that these engines are direct injection with the valves getting dirty doesn’t help.
The dealer process to approve a new engine is relatively simple. The check for sludge and confirm that the engine is seized. The they as for oil change receipts.
The workmanship on the new engine install leaves a lot to be desired. My trans lines were swapped and was having shifting issues when hot. Also had a radiator leak and now probably a low freon situation that is all probably due to this. The bottom engine covers were loose with quite a few bolts and screws missing. I know my car well as I do all the work myself and “baby” it. After 140K miles, all the engine cover bolts and pins were in immaculate shape, until now.

How did they test the alternator? Id say put a new battery in there and crank it. The NORMAL issue is that the alternator dies and so you kill your battery to the point it wont turn over because you sucked all the juice out. The fuel pump would “be going out” rather than just die and leave you stranded. But if that was the case id say the radio would still come on as the engine would die but the battery would be fully charged.

Just some preliminary stuff. I didnt read half the replies but just shooting my shot.

Why not?
Have you ever had a drain back up and upon disassembly find some foreign object lodged inside with years of sludge accumulation gathered up around it? How could a small amount of hair ever back up a drain? It’s impossible :wink:

There are all kinds of scenarios that seem unbelievable when things we don’t expect are part of the equation…

This is about the Hyundai engine problems . Where did you come up with alternator?

All I read was engine died and power died. Just wondering how they checked the alternator.