In May 2024, one of my coils went bad (car started misfiring, like it was going to stall). They replaced that coil. Six months later, same thing happened and they replaced another coil.
Then in October 2025, same thing happened on the way home from work. Had it towed back to the same shop and they replaced it under warranty.
Happened again in November. Same thing, had it towed, and replaced another one which was not technically under warranty but they took care of me anyway.
So my question is, why does this keep happening? What can cause coils to keep going bad? The repair guy was just like, “I don’t know, I just fix ‘em when they go bad.”
When one coil goes bad, it can mean the others will soon follow suit. That is why shops may recommend changing all of them at the same time. That way, you’re not coming back in a month or two each time the next one reaches end of life. Lots of people balk at the repair bill for all of the coils at once so some shops only replace the one that is currently dead and leave the others to die natural deaths in sequence.
Sounds like your guy is in the latter camp. Just fix the immediate problem and not proactively replace them if they are all the same vintage.
Now if a replaced coil fails prematurely afterward, it can be due to it being an aftermarket part that may not have the original OEM quality or there is something wrong with the engine that is causing them to fail. But in your case, it appears they were just failing in succession…
Your post describes one ignition coil going bad after another. Sounds perfectly normal. Your car has 4 coils, they are all the same age and have had the same use. Why wouldn’t they all fail around the same time?
Since they all have the same lifespan and they are all used identically, when one burns out it should be no surprise that the others will soon follow, right? Did your mechanic give you the option of replacing just one or all 4 at once?
Have the spark plugs been replaced on schedule on this car? Trying to throw a spark across a worn out plug can place added stress on a coil.
Agree with above, coils have the same amount of use, now, you didn’t tell us how many miles are on your Corolla?? 80K or 300K miles?? Is your spark plug tube seals leaking oil, that can cause the COP (coil on plug) boots to swell and the COP start arcing…
If the spark plugs have been replaced, were they replaced with the correct OEM spark plugs, and not the will fit spark plugs?? Almost always recommend installing the same plug that came out, matter a fact, I jut about refuse to install a non OEM spark plug, seen to many issues over 30+ years…
I’m a replace one coil at a time guy if they are easy to get to, but if they are hard to get to then I replace them all, I always give the customer the option for one or all… But if a 2nd one goes out fairly quick, then I just replace all the rest… And I almost always replace all the spark plugs when the 1st coil goes out…
My son has a 2008 Corolla and misfires were occuring. Instead of replacing one coil at a time we replaced all 4 plugs and all 4 coils. You have to remove the coils to change the plugs anyway. We used the Denso recommended plugs. The plugs and coils are very easy for a DIY’r to do. Have not had a misfire since then, about 3 years ago
