Sonata Hybrid (2016) - Car Shakes

This is a follow up to my original post, which is below. Here are my recent thoughts on the situation and also some symptoms that I’ve seen.

For many months I’ve been thinking that maybe I need new tires or an alignment because my car often feels shaky. I’ve come to realize that it seems to be related to my original question (below). The original situation that I mentioned is now happening more frequently. In addition, it seems like when I first drive the car in the morning, it’s a little shaky for awhile. If it gets too bad, the check engine light comes on for probably less than 10-15 seconds. I seemed to notice today that if I see the EV light come on than it’s driving smoother. I also noticed that when it feels shaky that my - instantly showing - gas mileage is lower and when it straightens itself out that the gas mileage is suddenly much better. When it’s shaky, it’s almost like the car is losing power, then when it smooths out, the car has power again. The check engine light rarely, if ever, will come on after 15 minutes of driving. It will also rarely come on if the car was previously driven less than 4 hours earlier. A couple of times recently, the control panel becomes dimmer than what I would expect and suddenly out of nowhere it brightens and then can out of nowhere dim again. I don’t feel like it used to work this way. My car also has trouble with the wipers turning off (this is infrequent and I do have a different post about this). The lights and the wipers are probably not related to the main problem, but I thought I’d mention it just in case.
I told my mechanic about changing the spark plugs. He didn’t think that was likely the cause, but he didn’t look. (I should have asked him to look.) The dealership wants $200+ just to diagnose this. (I might do this.)

I’m wondering if anyone has new thoughts about this.

Now and then my 2016 Sonata Hybrid will start shaking. The first time it happened, I was on the highway and it felt like I was driving over (mild) speed bumps (but I wasn’t). When it happens, which isn’t frequent, it usually happens on the highway less then 10 minutes after entering and it lasts less than 30 seconds (but feels like forever). The check engine light will turn on, but when I get the check engine light’s records checked (which I’ve done 3 separate times), they never see any record of it coming on. Admittedly, besides getting oil changes, I don’t get any regular maintenance done. Any thoughts? Any particular things I should have my mechanic look for?

Look for a misfire. Have your car’s error codes scanned with a proper scan tool. If the check engine light was set, it will be stored, at least for a while.

If the car has lots of miles, plan on new sparkplugs and maybe a coil or 2.

You repeat the question, I’ll repeat the answer. Nothing has changed except the calendar.


Did you ever change the spark plugs and coils?? You never did post any codes, check them and post them here…

Nevada posted this…


Jul 7

Likely an intermittent coil failure, those cars have a known coil problem:

16-01-003-1 Hyundai Technical Service Bulletin (

EDIT: Mustangman beat me to it… lol


What he said :point_up_2:

Basically the definition of insanity is to keep doing the same thing expecting a different answer…


Thank you for the response. I’ve had the error codes scanned three times. Each time they come up with nothing. I’ve been told if the check engine light goes away on it’s own that it doesn’t leave a code. Is this true?

In terms of miles, my car has 75000.

Thank you for the question and the response.

I asked my mechanic about changing them. He said (without looking at the car) that they wouldn’t need changing at 75000 miles. I know that I should have had him look - my mistake.

No, it isn’t true. A good scanner will read old codes not cleared even if the CEL is not currently on… Heck, even my cheap ones will.


My opinion Hybrid-take it to a dealership. Car electronics are complex, hybrids more so.
Telling your regular mechanic to change the plugs and coils might fix the problems as noted by the service bulletin.

This is why I would bite the bullet and go to dealership.

BTW , my understanding Sonata hybrids have a 10 year or 100,000 mile warranty. I would think that would cover the coils noted in the service bulletin.

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I can’t speak to whether your car’s computer will erase diagnostic codes stored when the CEL turns on. It probably varies car to car. But on most modern OBD II car-designs (like yours) there are three separate memories for storing diagnostic codes. Pending, current, and history. In your case the codes might have been moved from “current” to “history” when the CEL turned off. I think the advice above to pay a dealership for a proper diagnosis makes a lot of sense. They’ll have the Toyota scan tool which can access all of the memories. You aren’t automatically required to hire them for the repair. So once you have their info, you are welcome to post here for more ideas on how to proceed.

Thank you for the advice. I took it to the dealership first thing on Monday. They’ve driven it three or four times since then and only noticed one problem. The problem they noticed was “a slight rough idle”. They did not find any scan codes under active, pending, or history. While they’re driving it, they hook up some kind of machine that keeps a record of what’s happening when they drive it. The machine shows no problems. They suggested replacing the spark plugs and ignition coils - but only as a guess, because they don’t see anything wrong with them. I think “a guess” means that if I continue to have problems, they’re not liable, because it was only a guess. This procedure would cost me $1200. It’s Wednesday and they’re going to try again today. (Third day in a a row that they’re trying.) Hopefully they will see something. If they don’t find anything and I choose to have them do no maintenance, then I’m out $200 for a diagnostic fee. If I have them do something, then the fee goes away. I’m open to hearing any thoughts, ideas, or suggestions.

The dealership told me “the internal lubricated parts of the engine are covered by the powertrain”. Does this sound correct? Does this mean that the coils would not be covered?

If you read your warranty, the answer to that question will likely be contained within that writing.

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The powertrain warranty does not cover ignition coils, those were covered by the 5 year/50,000 mile basic new car warranty.

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The dealership decided not to charge me for the diagnosis. So, I’m back where I started. Now what???

How often is the check engine light on? How many days will a technician need to drive the vehicle to be able to observe the problem?

Just so you are aware of this…


I appreciate the information. Are you saying that maybe this applies to my current situation?

Ask your shop to lend you a scan tool so that you can stop the car & read the diagnostic codes yourself immediately after the CEL turns on. Whenever the CEL turns on, a diagnostic code should be stored at the same time. No idea why your diagnostic code isn’t visible in any of the three memories. I could see it being erased from the current memory if the problem let up temporarily, but it seems like it should still be in the history memory. Maybe this has to do with your car’s hybrid configuration.

Why would a dealership lend an expensive scan tool to a customer?


They might own an inexpensive version that only reads codes they’d be willing to lend to a good customer. In any event the worse they can do is say “no”.