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Multiple ignition coil failures within 2 weeks? Or what else is this?

A few weeks ago on a short drive, my car (2000 Toyota Corolla) started shuddering/pulsating when I was stopped at a red light (and it kept doing that intermittently as I drove the few blocks home.) Next time I tried to start it, it turned over but then died.
Towed it to the mechanic, he said it was a dead ignition coil, he replaced the coil and it was able to start again.

Less than a week (and not much driving - 50 miles tops) later, on the highway, it starts shuddering again, feels way underpowered, and the check engine flashes. It’s pretty scary. I pull over and have it towed to the mechanic. (It still starts up but doesn’t feel safe to drive, plus the check engine light is flashing.) First he says one of the fuel injectors needs to be replaced, then he says that on further testing it was actually another dead ignition coil. He replaces the ignition coil (he didn’t end up replacing the fuel injector) and I pick up the car.

It’s fine on the drive home (which is about 3 city miles, no highway driving) and on another neighborhood errand, and the check engine light isn’t on, but now it’s sort of shuddering again. I don’t want to keep driving it and/or try it on the highway to wait for it to get worse.

I guess I’ll take it in again tomorrow, but does this seem odd at all? I know some people replace all 4 ignition coils at once pre-emptively, but it would seem strange for 3 to fail within ~150 miles (assuming this is yet another ignition coil.) What else might be going on? I had the spark plugs changed last year so those should be fine. The car has pretty low miles on it (about 100k) for the age.

Manufacturers have statistical calculation regarding failure down to a science:
I bought a set of Philips lightbulbs once that all failed within days of eachother, after replacing them pretty much all at the same time two years before. I know because we had just moved into the house.
Long story short, it could be that they all failed because their time was due.

The problem might be with the Ignition Control Module.

The ICM functions in two modes. These are the Start and Run modes. When starting the engine, the ICM allows full battery voltage to the coil. This ensures there’s a hot enough spark to start a cold engine when the fuel mixture is rich, and the battery is dragged down from the starter. Once the engine starts, and the ignition switch moves to the run possition the ICM goes into the Run mode. The ICM then drops the voltage to the ignition coil(s) because when the charging system comes on line the voltage can hit 14.5 volts.

So if the ICM fails to go into Run mode once the engine starts, and is still in the Start mode you’ll fry coils.


All good ideas above. I’ll add that the wrong spark plug (i.e. not one of the exact makes/part numbers recommended in the owners manual) or too wide of a gap could stress the ignition coils. Likewise, spark plug wires which are arcing and needing replacing. If this car uses a distributor and rotor, a bad rotor or distributor cap could do it too.

What should I reasonably be expecting from my mechanic at this point? This will be the third time I’m taking it in. He generally seems honest and was rated well in the mechanics files here.
Should he have looked into those things–failing ICM, spark plug issues, etc–when the second ignition coil failed so soon afterwards to see why that might have happened? I think he didn’t just replace all 4 coils at once because he knows I’m on a budget (although he also didn’t ask me what I preferred, to replace 1 or all 4.)

This is tough to call because it’s unknown as to how the mechanic arrived at his conclusions and any codes that are or were involved are unknown to us.

Is it always the same cylinder coil that is failing, i.e. always the coil for cylinder #2 for example?

It appears that the individual coil and igniter comes as a unit, i.e. the igniter is part of the coil on plug assembly.

Hope this

no, this has been 2 different ones, #2& #3.

most recent codes were p0301, p0302, p0303, & p0304

it sounds like the most recent time it was hard to diagnose. as I said, they eventually diagnosed it as another bad coil & replaced it, BUT to be honest I’m not sure if that even actually solved the problem since
a) it was able to start when I brought it in the second time so there is no clear “well, it didn’t start when I brought it in and now it does” like the first time, and
b) it started having the same issue again (shuddering when I was stopped at red lights) within 5 miles of driving, and this seems like an issue that can be sort of intermittent.

Along with the other things mentioned I suggest you check for faulty engine grounds and see if there is any possible issue with the charging system. Make sure the DC voltage and AC ripple voltage are where they should be.

Well, this is the issue: while I try to learn about what might be happening in my car, any work will actually be done by my mechanic. I don’t want to pay to replace the other 2 ignition coils and then either a) have the same problem continue because it was something else or b) have the replaced coils burn out again because something else was wrong with the car and caused that.

I don’t know enough to know if the mechanic was negligent in perhaps not investigating whether something else was happening to make coils burn out one after another.

Hopefully when the plugs were replaced they used OEM ones since different manufacturers can react differently.

MIsfires are easier to diagnose if the shop has the manufacture’s scan tool and updated software. Also, certain makes/model/years are prone to different types of misfires. Experienced mechanics know where to start based on the car involved to minimize diagnostic time If the shop doesn’t have the car maker’s scan tool, they’ll do the best they can, which is usually to start swapping things around and seeing if the misfire follows the swap. For example, they may swap the spark plugs from one cylinder to another, the wires (if possible), the coils, etc. They’ll swap injectors too, but before swapping fuel injectors, usually they will probe for pulses at the injector electrical inputs first. Also before swapping injectors, they’d do a fuel pressure test, as that is easier than swapping injectors. If there are other codes besides the P030X codes, that can be helpful too. Bad compression can be a cause, and is fairly easy to test, so that will be high on the agenda. With multiple misfires, they’ll look at the fuel trim values to determine if any of the banks are running rich or lean, which can cause misfires. Vacuum leaks and intake manifold leaks, anything allowing unmetered air in will cause misfires. A faulty coolant temp sensor can cause multiple cylinder misfires. EGR and PCV faults can cause misfires too, and both are fairly easy to check, and would be done before doing the more time consuming tests. It always makes sense when things seem to get bogged down to go back to square one: bring all routine engine maintenance up to date according to the schedule in the owner’s manual. Often the problem will be found or at least eliminated just by doing this.


Several manufacturers have had issues with coil on plugs, and have come out with improved parts to address those issues

When an “early” coil on plug fails, it’s very common to have the others also fail soon after, until they’ve all been replaced with “the latest and greatest”

I’ve seen customers make several trips to the shop, to have their coil on plugs replaced, one at at time, as they fail. It would have been easier to replace them all at once.

I think someone here mentioned Ford has had a problem with coil on plugs on some of their cars.

Thanks. They did test the compression the second time and found it to be fine.

@db4690, when you say manufacturers had issues with “coil on plugs” and have improved parts, do you mean the coils or the plugs?

When I had the plugs changed last year, I purchased them at a parts store (I was going to try to do it myself but ended up chickening out) and had a (different) mechanic install them. I believe I got Denso or NGK Iridiums that were “OEM recommended.” I checked into it a bunch first.

I don’t have a whole lot of money to throw at this. The car has some other issues that mean it probably won’t last as long as Corollas often do.

The replacement plugs you purchased should be fine I would think. If they were Champion or Bosch then there possibly might have been an issue. Has this latest issue been proven to be another coil problem? Are there any error codes being generated for clues to the problem?

Hasn’t been diagnosed yet; no check engine light, I don’t own a code puller, & I’ve been debating whether to take it back to this same mechanic… I guess it makes sense to but I feel a bit unsure about them at this point.


coil on plug means the coil

It literally means the individual coil sitting on top of the plug . . . versus the old days when there was one coil with ignition wires going to the individual plugs

I certainly hope you used the correct Denso or NGK plugs

I haven’t seen anything from what you report that would indicate you need to change mechanics. I expect your mechanic will figure it out in due course. When you speak w/your mechanic, make sure you are telling him your objectives, not how to accomplish them. You can ask for his ideas, like, you can say “Would you recommend the egr be checked for sticking for a symptom like this?”. But don’t just order him to check the egr. You want to keep the mechanic on your good side I guess is what I’m saying here. If he’s a successful mechanic, he already knows how to do the job. These drivability problems can take some time to sort out. If you do change mechanics, for drivability problems like this, I suggest you make sure you use a dealer shop, or an inde that specializes in your make of car. You need someone who has the specialized scan- and diagnostic-tools for you car, and only a shop that specializes in your car’s make will likely have all of them.