Mazda PE20-18-100A Ignition Coil: Skyactiv Misfire Symptoms, Fitment and Why Coil-On-Plug Came Back

A 1908 Model T did not have an ignition coil. It had four of them, mounted in a varnished wooden box on the firewall, each one a "trembler" coil with a vibrating contact that hammered open and shut to build a spark. You could identify a Ford idling a block away by the chatter of those coils. Then the industry found a tidier answer: one coil, one distributor, a set of points, and a spinning rotor handing the spark around to each cylinder in turn. That arrangement ran essentially every gasoline car for the better part of eighty years.

And then it went right back to where it started. Open the hood of a modern Skyactiv Mazda and there are four coils again, one per cylinder, sitting directly on top of the spark plug. No distributor, no rotor, no plug wires. The Model T had the right idea. It just took eight decades and an engine computer to do it properly.

What the PE20-18-100A is

The genuine Mazda PE20-18-100A ignition coil is $189.99 for one coil. The listing specifies Mazda as the brand, PE20-18-100A as the manufacturer part number, coil-on-plug as the type, and lists application to the 2.0L and 2.5L Skyactiv engines used in the CX-5, CX-9, Mazda3 and Mazda6.

Let us be straight about the price: that is dealer-parts money for one coil, and it is a genuine Mazda part rather than a $22 box off a marketplace. Some people want exactly that and nothing else, particularly on a car that has already eaten a cheap coil. As always, verify the part number against your own VIN before you buy — across a range that spans four model lines and two displacements, the part number is the only thing that settles fitment.

What a dying coil feels like from the driver's seat

Coil failure is rarely sudden. The usual arc is a stumble on cold start that clears up once warm, then a rough idle you can feel through the seat, then a shake under load going up a grade or merging onto the 60. Fuel economy drops. Sometimes it only misbehaves in the rain, because moisture is finding a crack in the coil boot.

Then the check engine light. A steady light with P0300 means a random misfire the computer cannot pin to one cylinder. P0301 through P0304 name the cylinder outright — that is the useful one. A flashing check engine light means an active misfire severe enough to dump raw fuel into the exhaust, and that is the one where you pull over. Unburned fuel lighting off inside a catalytic converter is how a $190 coil becomes a $1,200 repair.

The five-minute test that saves you money

If you have P0302, move the coil from cylinder 2 to cylinder 3, clear the code, and drive it. If the code comes back as P0303, the coil is bad and you found it without spending a dollar. If it stays P0302, the problem is the plug, the injector or compression in that cylinder — not the coil. Do the same swap with the spark plug to split the difference.

Two habits worth having. Replace the plug whenever you replace a coil: a worn plug with a wide gap makes the coil work harder, and is often what killed it in the first place. And if the car is past 100,000 miles and one coil has gone, budget for the set rather than making four separate trips under the hood over the next year.

Other engine-bay parts on the shelf right now

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