What Resets the Check Engine Light
The check engine light turns off in three ways: the problem that triggered it goes away on its own, you fix the underlying problem, or you clear the diagnostic code from your vehicle's computer. Most of the time, the light stays on until one of these things happens — it does not reset itself after a set number of days or miles.
If you want to turn off the light yourself right now, you have two practical options: use an OBD-II scanner (a handheld device that plugs into your car's diagnostic port), or disconnect your vehicle's battery for 15 minutes. A mechanic or auto parts store can also clear it for you, usually for free or a small fee. The catch is that clearing the code does not fix what caused the light to come on — if the underlying problem is still there, the light will come back.
Key Takeaways
- The check engine light stays on until the problem triggering it is fixed or the diagnostic code is manually cleared from your car's computer.
- You can clear the code yourself with an OBD-II scanner (costs $25 to $100 to buy, or free to borrow), or by disconnecting your battery for 15 minutes.
- Many auto parts stores will read your diagnostic code for free and tell you what triggered the light, which helps you decide whether to fix it or just clear it.
- Clearing the light without fixing the problem means it will come back, sometimes within days or weeks.
- Some problems (like a loose gas cap) fix themselves; others (like a faulty oxygen sensor) need repair to prevent the light from returning.
Using an OBD-II Scanner to Clear the Code
An OBD-II scanner is a small handheld device that reads and clears the diagnostic codes stored in your vehicle's computer. You plug it into the OBD-II port, which is located under the steering wheel on the driver's side of most cars made after 1996. The port looks like a rectangular connector about the size of a USB port.
To clear the code: turn on the ignition (do not start the engine), plug the scanner into the port, navigate to the "Clear Codes" or "Erase Codes" menu on the scanner's screen, and confirm. The light should turn off within seconds. Basic scanners that only clear codes cost $25 to $50; more advanced ones that also read what triggered the light cost $50 to $100. Many auto parts stores let you borrow a scanner for free if you buy a part from them, or you can rent one for a few dollars.
Disconnecting Your Battery
Disconnecting your vehicle's battery for 15 minutes will clear the diagnostic code and turn off the check engine light. This method works on all vehicles and requires no tools beyond a wrench or socket that fits your battery terminal bolts.
To do this: turn off the engine, open the hood, locate the negative battery terminal (marked with a minus sign or black cable), loosen the bolt holding the negative cable to the terminal, and disconnect the cable. Wait 15 minutes, then reconnect it and tighten the bolt. The light should be gone when you start the engine. Note that this will also reset your radio presets, clock, and any other settings stored in your car's memory. This method is free but less precise than a scanner — you cannot see what code triggered the light before clearing it.
Getting Your Code Read Before You Clear It
Before you clear the light, you should know what triggered it. A diagnostic code tells you whether the problem is serious (like a faulty catalytic converter) or minor (like a loose gas cap). Many auto parts stores will read your code for free using their own scanner.
To get your code read: drive to an auto parts store, tell them your check engine light is on, and ask them to scan it. They will plug in their scanner, read the code, and print out a report explaining what the code means. This takes 10 to 15 minutes and costs nothing. Once you know what the code is, you can decide whether to fix the problem, clear the light and monitor it, or take the car to a mechanic. If the code is something like P0171 (fuel system too lean) or P0300 (random misfire), the problem usually needs repair. If it is P0455 (loose gas cap), you can just tighten the cap and clear the code.
When the Light Comes Back After You Clear It
If you clear the check engine light without fixing the underlying problem, the light will come back. How long this takes depends on the problem — some issues trigger the light again within a few days of driving, while others may take weeks or months.
If the light returns, the same diagnostic code will usually come back with it. This tells you the problem is still there and needs attention. Some problems are intermittent (they happen only under certain driving conditions), so the light might stay off for a while and then come back. If you clear the light multiple times and it keeps returning with the same code, you should have a mechanic diagnose and repair the issue rather than continuing to clear it.
Common Problems That Trigger the Light
A loose or missing gas cap is the most common reason for a check engine light. Tighten your gas cap and clear the code — if the cap was the problem, the light will not come back. Other minor issues include a faulty oxygen sensor (usually costs $100 to $300 to replace) or a bad catalytic converter (costs $400 to $2,500 to replace). More serious problems include engine misfires, transmission issues, or emissions system failures.
The diagnostic code your scanner reads will tell you which system is having trouble. A code starting with P0 refers to the engine or emissions system; P1 codes are manufacturer-specific. Once you know the code, you can search for it online or ask a mechanic what it means and whether the problem is urgent. Some problems (like a faulty oxygen sensor) will not prevent you from driving safely, but others (like a severe misfire) can damage your engine if ignored.
When to See a Mechanic Instead
If your check engine light is flashing (not steady), the problem is urgent and you should not drive the car except to a mechanic. A flashing light means the engine is misfiring or there is a serious emissions problem that can damage your catalytic converter if you keep driving.
You should also see a mechanic if the light comes back repeatedly with the same code, if you do not know what the code means, or if the light is accompanied by other symptoms like rough idling, loss of power, or unusual noises. A mechanic can run a full diagnostic, tell you what is wrong, and repair it properly so the light does not return. This costs more than clearing the light yourself, but it solves the actual problem instead of just hiding the warning.
Frequently Asked Questions
Will the check engine light turn off by itself if I just keep driving?
No. The light will stay on until the problem is fixed or the code is cleared. Some problems (like a loose gas cap) may go away on their own, which will turn off the light, but most problems stay until you repair them or manually clear the code.
Is it safe to drive with the check engine light on?
It depends on the problem. If the light is steady, the car is usually safe to drive, though you should have it checked soon. If the light is flashing, do not drive except to a mechanic — a flashing light means the engine is misfiring and you risk serious damage.
Can I clear the check engine light without a scanner?
Yes. Disconnecting your battery for 15 minutes will clear the code and turn off the light. This method is free but will also reset your radio and clock settings. A scanner is more precise because it lets you see what code triggered the light before you clear it.
What does it mean if the check engine light comes back the same day I clear it?
It means the problem is still present and active. The same diagnostic code will likely come back. You should have the issue diagnosed and repaired by a mechanic rather than continuing to clear the light.
How much does it cost to have a mechanic clear the check engine light?
Many mechanics will clear the code for free if you bring the car in for a diagnostic. If you just want the light cleared without a diagnosis, some shops charge $50 to $100, though many auto parts stores will do it for free.