How to Turn Off Your Check Engine Light

What the check engine light means and why it turns on

Your check engine light turns on when your vehicle's onboard diagnostic system detects a problem with the engine, emissions system, or transmission. The light itself does not tell you what the problem is — only that your car has stored a diagnostic trouble code in its computer. That code is the actual clue to what needs fixing.

The light may appear as a steady glow or a flashing light. A steady light usually means the problem is not urgent, though you should still have it checked soon. A flashing light means the engine is misfiring or running rough, and you should stop driving and get service right away — continuing to drive can damage the catalytic converter, which is expensive to replace.

The check engine light will not turn off by itself once the code is stored, even if the problem goes away temporarily. You have to clear the code from the computer after you fix the underlying issue, or sometimes even before you know what the issue is.

Key Takeaways

The check engine light indicates a stored diagnostic trouble code; the light itself does not identify the specific problem.
You can read the code yourself with an inexpensive code reader, or a mechanic or auto parts store can read it for you at no charge.
Fixing the actual problem — not just clearing the code — is what stops the light from coming back on.
Once the problem is fixed, you can clear the code yourself with a code reader, or a mechanic will clear it during service.
A flashing check engine light means stop driving when ready; a steady light allows you to drive to a repair shop.

Reading the diagnostic code yourself

The fastest way to find out what triggered your check engine light is to read the diagnostic trouble code. You can do this yourself with an OBD-II code reader (OBD stands for onboard diagnostics). These devices plug into a port under your steering wheel or dashboard — the port looks like a rectangular connector about the size of a phone charger. Most vehicles made after 1996 have this port in the same location.

Code readers range from basic models that cost $20 to $50 and only display the code number, to more advanced versions that cost $100 to $300 and show descriptions of what the code means. For a first check, a basic reader is enough. Plug it in, turn your key to the "on" position without starting the engine, and the reader will display the code — usually a letter followed by four numbers, like P0301 or P0420.

If you do not want to buy a reader, many auto parts stores (including AutoZone, O'Reilly, and Advance Auto Parts) will read the code for you at no charge. Call ahead to confirm, bring your vehicle keys, and they will plug in their reader in the parking lot. Write down the exact code they give you.

Understanding what the code means

Once you have the code number, search for it online along with your vehicle's year, make, and model. Codes beginning with P0 are the most common and usually point to engine or emissions problems. A P0300 code, for example, means random cylinder misfires. A P0420 means the catalytic converter is not working efficiently. A P0171 means the engine is running too lean (not enough fuel).

The code narrows down the problem but does not always pinpoint the exact cause. A P0301 could mean a bad spark plug, a fuel injector problem, a vacuum leak, or a compression issue. This is where a mechanic's experience matters — they can run additional tests to find the root cause. If you want to attempt a fix yourself, research the code for your specific vehicle model, as the same code can have different causes depending on the engine.

Some codes point to straightforward fixes you can do yourself: replacing spark plugs, tightening a loose gas cap, or replacing an air filter. Other codes require professional diagnosis and repair. If the code is related to the transmission, catalytic converter, or fuel system, professional service is usually necessary.

Fixing the problem that caused the code

The check engine light will not stay off unless you address the underlying problem. straightforward clearing the code without fixing the issue will cause the light to come back on within a few days or weeks, once the computer detects the problem again.

If the code points to something you can fix yourself — like a loose gas cap, a clogged air filter, or worn spark plugs — fix it first. If the problem requires professional repair, take your vehicle to a mechanic. Bring the code number with you so the mechanic knows where to start. Many shops will diagnose the problem for a fee (usually $50 to $150), though some will waive the fee if you have them do the repair.

After the repair is complete, the mechanic will clear the code as part of the service. If you fixed the problem yourself, you can then clear the code using your code reader or by having an auto parts store clear it for you.

Clearing the code after the repair

Once the underlying problem is fixed, you need to clear the diagnostic trouble code from your vehicle's computer. This tells the computer to stop displaying the check engine light. There are three ways to do this:

Using a code reader: If you own an OBD-II code reader, plug it in, navigate to the "clear codes" or "erase codes" menu, and follow the prompts. The exact steps vary by reader model, so check your reader's manual. After clearing, the light should turn off when ready.

At an auto parts store: Many auto parts stores that read codes for free will also clear them for free. Call ahead to confirm they offer this service.

At a repair shop: Your mechanic will clear the code as part of the repair service. If you took your vehicle in for diagnosis only and decided to fix it yourself, some shops will clear the code for a small fee or for free if you ask.

What to do if the light comes back on after clearing

If the check engine light returns within a few days or weeks after you cleared it, the original problem was not fully fixed, or a new problem has developed. Read the code again using the same method as before. If it is the same code, the repair did not work and you need to go back to the mechanic or try a different fix. If it is a different code, a separate issue has triggered the light.

Do not ignore a returning check engine light. Each time it comes back, it means your vehicle is still not running as designed, and continuing to drive it can cause additional damage. Have it diagnosed again and address the root cause rather than repeatedly clearing the code.

When to seek professional help when ready

Some situations require a mechanic right away, even before you read the code. If the check engine light is flashing, your engine is misfiring and you should not drive the vehicle except directly to a repair shop. Continuing to drive can overheat the catalytic converter and cause thousands of dollars in damage.

If your vehicle is also showing other warning signs — rough idling, loss of power, strange noises, or a burning smell — do not delay. These combined with the check engine light suggest a serious problem. If you are unsure whether the problem is urgent, err on the side of caution and have it checked by a professional rather than attempting a fix yourself.

Frequently Asked Questions

Can I drive with the check engine light on?

If the light is steady, you can usually drive to a repair shop, though you should have it checked soon. If the light is flashing, stop driving when ready — flashing means engine misfires, which can damage your catalytic converter. Pull over safely and call for a tow or drive directly to a nearby mechanic.

Will the check engine light turn off on its own?

No. The light will stay on until you clear the diagnostic code from your vehicle's computer. Even if the problem fixes itself temporarily, the code remains stored and the light stays on. You must clear the code manually after the problem is resolved.

What does it mean if I have multiple codes?

Multiple codes usually mean either one problem is causing several related codes, or several separate problems exist. Write down all the codes and research them together with your vehicle's year and model. A mechanic can determine whether they stem from one issue or multiple issues.

Is it safe to clear the code without fixing the problem?

Clearing the code without fixing the problem is not unsafe in the short term, but the light will come back on once the computer detects the problem again. You will be back where you started. It is better to fix the problem once and clear the code permanently.

How much does it cost to fix a check engine light?

The cost depends entirely on what caused the code. A loose gas cap costs nothing to tighten. Spark plugs might cost $50 to $300 depending on your vehicle. A catalytic converter can cost $400 to $2,500. Have the code read first so you know what you are dealing with before you commit to a repair.

This guide is for general information only and is not medical, financial, legal, or other professional advice. For decisions specific to your situation, consult a qualified professional. See our Editorial Policy.