If the light is steady and the car drives normally, you can usually keep driving for now and get it checked soon. If the light is flashing, or you also see a hot temperature gauge, an oil pressure warning, smoke, a burning smell or a big loss of power, stop as soon as it is safe. The code tells you which case you are in.
This is the most common case. The computer stored a fault, and many of them are about emissions: the gas cap, an oxygen sensor, the catalytic converter, a thermostat that lets the engine run cool. None of that is an emergency.
Do not leave it for months, though. Some of these faults cost you gas mileage, some grow into bigger repairs, and while the light is already on you will not notice when a second problem shows up.
Misfires are happening right now, and they can damage the catalytic converter. Drive gently to a safe place or a shop, today. Our guide to a flashing check engine light walks through it.
These can mean damage within minutes. The check engine light code is only part of the story.
Every scan ends with one of three levels: Stop driving soon, Get it checked this week, or OK to drive, fix when convenient. Some codes always start high no matter what: misfires, overheating and low oil pressure start at this week or higher, and a flashing light is always Stop driving soon. We never tell you a car is safe. We tell you what to watch for.
Read the code. With an adapter, the app does it in about a minute. Without one, many auto parts stores read codes for free, and you can look up the code here.
There is no fixed number. With a steady light and a car that feels normal, most drivers have days or a few weeks to get it checked. With a flashing light or any of the stop signs above, the answer is: not far.
The light always means the computer stored a fault, but some faults are minor, like a loose gas cap, and some clear on their own. Reading the code is the only way to know which kind you have.
The light itself does nothing. The fault behind it might, slowly. Oxygen sensor and fuel mixture problems can lower your mileage, and an ignored misfire can damage the catalytic converter.
Estimates only. A mechanic should confirm. If the car shows a hot temperature gauge, an oil pressure warning, smoke or a burning smell, stop as soon as it is safe.