Why does my check engine light keep coming on and off?

I’ve got a 2016 Kia Soul, just the base model. A month ago, the check engine light started coming on, but I can’t afford to take it to a shop right now. I recently changed the oil, got all four tires replaced because of nails and wear (there’s a ton of construction where I live), and even had to replace the battery shortly after buying the car. It’s mostly stock, and I just hit 100k miles (I bought it at 80k about a year and a half ago).

What’s weird is the engine light isn’t consistent. Some days it’s off completely, some days it’s on as soon as I start the car, and other times it’ll turn on randomly during the day. Another thing I’ve noticed is that the car rumbles a bit when it’s idle—whether it’s at a stop sign, light, or even in park. It’s not constant, just a quick shake for a second, then it stops. Should I be worried?

Oh, and the rumble has been there since I bought the car.

My check engine light does something similar when it’s rainy or humid. My gas cap doesn’t seal properly anymore, so that might be causing it. I used a code reader, and it says I’ve got a small exhaust leak. I’ve got a 2015 Kia Soul—the one with the oily, burny smell.

It could be an emissions issue. You can get a cheap Bluetooth OBD2 code reader from Amazon that works with free apps. That way, you can check what’s causing the light and figure out if it’s something serious.

If you’re in the US, places like AutoZone will read the code for free. It’s super easy.

DeeMario said:
If you’re in the US, places like AutoZone will read the code for free. It’s super easy.

Yep, that’s true. And smaller mechanic shops might also check it for free if you give them a heads-up.

If it’s emissions-related, you could try running some fuel injection cleaner through your tank—it might help for a while. But if it’s the catalytic converter, you’ll either need to replace it eventually or just live with the light on.

Make sure to check your oil regularly, like once a week. That way, you’ll catch any issues early.