Back to basics: finding a bad coil with a simple test

Paige Fisher · 2026-03-08T10:06:31.575091+00:00

Cars keep getting more advanced every year. It feels like you need a degree in computers just to read codes. But I had a win last week that reminded me of the good old days. A sedan came in with a check engine light for a random misfire. The scanner pointed to a cylinder but didn't say why. Instead of guessing, I did the old pull-the-wire test while it ran. Found one coil wasn't firing right and fixed it fast.

paul_morgan6mo ago

What made you use the old test instead of the scanner?

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coleman.avery6mo ago

That bit about needing a computer degree to read codes, that's everywhere now. We keep adding layers of tech that just hide the simple fix. Like my home thermostat needs an app update before it can heat the house, or a coffee maker with a touchscreen that fails but the brew basket still works fine. Sometimes the old way is just the direct path to what's actually broken.

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barbaramurphy6mo ago

It's that layer of extra steps that gets me. The scanner gave you a place to start, but your hands-on test gave you the real answer. I see it with my grandkids and their toys, even. Batteries are dead, but instead of just opening the compartment, you have to unscrew three panels and decode a blinking light first. The direct path gets buried under all the extra stuff that's supposed to make it easier.

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