2018 Hyundai Sonata - Wiring issue

I purchased my 2018 Sonata 5/2018. I took it in for it’s 1st check up & oil change 1/22/19 @ only 4k miles. They also did an ‘update’. As I drove home, the car was losing power. Took it back to the dealer who finally determined it needed a new major harness. Still waiting for my car 2/12/19. How bad is this? Potential future problems? Other thoughts? Thanks!

Bad enough to deprive you of your car.

Impossible to guess. I suspect this is a build quality issue - wiring harness damaged during assembly that is a part, not normally in stock, so there is a long wait. It may get fixed and the car will be great for you. Or it might have other problems.

You have a very long warranty and most states in the US have lemon laws that cover such things. You might want to research the lemon laws where you live just to see what YOU need to keep, note and collect to exercise them, just in case!

If the Hyundai manual for 2018 still says 7500 miles or 6 months, you have voided your engine warranty by waiting 8 months and two days.

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Is Hyundai providing you a car to use gratis while yours is being repaired? If so, no worries, keep on piling the miles on their loaner at their expense while they fix your car. It’s a freebie!!

A wiring harness is nothing but a bunch of wires and connectors. If you need a new one, the only question to ask is why?, I guess. I mean they make the cars so shouldn’t they be also able to make a wiring harness that works for you car? Suggest you seek out more info on what exactly is wrong w/your old wiring harness and why it needs to be replaced. Normally a wiring harness problem can be addressed by repairing only the problematic section. I don’t see any info for the 2.4 L normally-aspirated engine on that topic. You don’t have the hybrid or turbo engine, right?

I am currently struggling with the same issue. It took Hyundai 3 weeks to produce the wiring harness. They had my car for over 30 days. I got it back today and pulled out of the dealership only to have the same issue and have to return the car. They are replacing the wiring harness again. Still waiting… #lemon

Did you research lemon laws in your state? If the dealer can’t fix it in a predetermined number of tries, Hyundai is required to replace the car. Your u must have receiptfor every visit. If they didn’t give you a receipt, try to get one.

Both owners should call Hyundai Corporate. The numbers should be in your Owner’s Manual. And document everything.

I’m going through the same thing right now, 2017 Sonata took it into dealership last Friday for oil change. Service writer says Hyundai issued a recall for a software update for the knock sensor. Would we like it done then? Sure, why not. On the way home, check engine light is flashing, there’s a bad misfire under acceleration. Drive back to dealer, they give me a rental, i go home. talk to service writer later that day, his tech says “needs a new engine wiring harness, have to order it, car will be ready Monday”. Talk to service writer today, that harness didnt work. Tech called Hyundai, their support staff said replace main engine harness. The one they had first told him to change was a sub-harness. With all the harnesses they are sending out, Hyundai should notice that they have a problem here, and figure out how to roll back their software update,


Just an observation by a uneducated guesser, but it looks like Hyundai service may be using a repair philosophy of “if there’s a problem, then the wiring harness has to be replaced” . Sort of like “if the only tool you own is a hammer, every problem looks like a nail”. Wouldn’t it make more sense to trace the circuit out, and measure for the appropriate voltage etc at the test points first?

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So the update is the 953 Campaign that they update the knock sensor. This is because the 2.4 GDI engine is prone to failure and they want to give the driver a warning by making the car go in limp home mode. It is kind of a CYA measure.
Now, some cars have the wiring harness issue after the update and some end up needing a new engine.
It is a bit of a mess in Hyundai now. They are working on it.

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… and in some states, the aggrieved car owner has the option of a full cash refund from the manufacturer.

It behooves people to carefully read the details of the Lemon Law in their own state, to retain documentation of all repair attempts, and then to file a claim with the manufacturer as soon as the dealer has been unsuccessful with the number of repair attempts (usually three) and/or has reached the maximum allowable repair time specified in that Lemon Law.


Certainly seems like an easy correlation to make. We just did a firmware update and suddenly a harness goes bad? Hmmmm…


Not necessarily. Chrysler did a firmware update on the Pacifica PHEV to prevent fuel injection before the ignition electronics were activated. The raw gas made its way into the catalytic converters and damaged them. Eventually, the damaged converters got hot enough that they started igniting the gasoline, resulting in extremely hot exhaust system ahead of the catalytic converter. Because the fire was inside the exhaust, it didn’t result in an engine fire, but there was significant damage. The firmware update was last summer, and I still see a new report at safercar.org every month. So, the repair did not cure the problem. It just took a while longer for the problem to show up.

Aside: spell check changed “firmware update” to “fairway R.E.M.” How 'bout dat?

I must assume you got a free loaner car, let them keep it for however long until it is fixed.

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I’m specifically referring to the post above. The effects were immediate yet rather than suspect the update they just performed, the wire harness in a basically brand new car just happened to fail driving out of the dealer lot?

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Just an update to my earlier post… Got s call from the service manager yesterday. He had ordered the new engine harness from Hyundai and they informed him no more were available now and he could expect it on March 6th.

March 6 is not a long time to wait, however the question I would be asking is what if this new wiring harness does not fix the problem? As others have correctly pointed out, it seems very unlikely that a wiring harness would suddenly fail–with no obvious physical damage–immediately after doing a firmware update. This sounds to me like a software/sensor problem, which will not be resolved by changing the wiring harness.

They either fix it or buy out the lease early. I don’t care how they fix it.

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The reason for the wiring replacement after the software update is that if the knock sensor wiring isn’t properly shielded, signal interference can occur, the PCM may interpret this as a bearing failure and the PCM will go into limp mode.

that’s an interesting point.
so, Hyundai decided to skimp the proper shielding and compensates in software?!?
I have a spot next to my workplace, where doors remote control needs to be within a foot of receiver by the windshield to work, otherwise RF interference from some radiostation (???) or whatever around does not let it work, works just fine anywhere else and batteries are fresh.
so… by this rationale, I can imagine I can get Hyundai vehicle to enter limp mode because of some external RF interference to to its knock sensor… at least theoretically… :slight_smile: