Check Engine Light On? What It Means and What to Do
The check engine light is your car's way of saying the computer saw something it didn't like. Sometimes it's minor. Sometimes it's not. Here's how to tell the difference and what to do next.
By the Allen's Automotive Service team in Metairie ·
Steady or flashing? That's the first question
Steady light: the car found a problem, but it usually isn't an emergency. You can generally drive it to the shop. Don't ignore it for weeks, though. A small problem left alone can turn into a bigger one, and while the light is on, a second problem can't warn you.
Flashing light: this usually means the engine is misfiring badly enough to damage the catalytic converter. Slow down, avoid hard acceleration, and get the car looked at as soon as you can. If it's flashing and the car is shaking or losing power, pull over somewhere safe and call us at (504) 780-9804.
Common reasons the light comes on
- A loose or worn gas cap. The fuel system is sealed, and a cap that doesn't seal can set a code. It's the first thing to check.
- Oxygen sensors. They tell the computer how the engine is burning fuel. When one goes bad, gas mileage often drops.
- Spark plugs or ignition coils. Worn plugs or a failing coil cause misfires, rough idle and hesitation.
- Evaporative (EVAP) system leaks. A cracked hose or bad valve in the system that captures fuel vapor.
- Airflow sensor or vacuum leaks. These throw off the air-fuel mix and can make the car stall or idle rough.
- Catalytic converter. Often the result of another problem, like misfires, that was left alone.
What a free code reading does and doesn't tell you
A code reader pulls a code like P0301 (cylinder 1 misfire). That tells you where the computer saw the problem, not what part failed. A misfire on cylinder 1 could be a plug, a coil, an injector, a wiring problem or a vacuum leak. Replacing parts based on the code alone is how people spend money and still have the light on.
When you bring it to us, we read the codes, look at the live data and freeze-frame data (what the engine was doing when the light came on), and test the part the code points to before we tell you what it needs. More on that on our check engine light diagnostics page.
What you can do before you call
- Check the gas cap. Tighten it until it clicks. If it's cracked or the seal is torn, replace it.
- Pay attention to how the car feels. Rough idle, shaking, hesitation, a smell, or worse gas mileage are all useful to tell us.
- Watch the temperature gauge and the oil light. If either of those comes on with the check engine light, stop driving.
- Write down when it came on. Right after getting gas? On the highway? After a heavy rain? It helps.
The light went off by itself. Am I good?
Maybe. Some problems are intermittent, and the car turns the light off after several trips without seeing the problem again. The code is usually still stored, though. If it comes back, bring it in and we'll read the history.
Why we don't just clear the code
Clearing the code turns the light off. It doesn't fix anything. If the problem is still there, the light comes back, sometimes after you've already left for a long drive. We'd rather find the cause. Planning a trip soon? See our pre-trip car check.
Questions we get
Can I drive with the check engine light on?
If it's steady and the car drives normally, you can usually drive it to the shop. If it's flashing, or the temperature or oil light is on too, don't keep driving it.
Will a loose gas cap really turn on the check engine light?
Yes. A cap that doesn't seal lets fuel vapor escape and the car's computer flags it. Tighten it, and if that was the cause the light should go off on its own after some driving.
Do you charge to look at a check engine light?
Call (504) 780-9804 and we'll explain how diagnosis works for your car. Any repair starts with a free written estimate, and nothing gets done until you say so.
Related
This is general information, not a diagnosis of your car. Every car is different, so call us with your year, make and model, or bring it by.
Ready to get it looked at?
Call (504) 780-9804 or book online.