How to Check Check Engine Light Codes: 3 Easy Ways
To check your check engine light codes, connect an OBD2 scanner or Bluetooth reader to the port under your dashboard, turn the ignition on, and read the codes, or have them read for free at an auto parts store that offers the service. The code (for example, P0455) tells you which system triggered the light. Before anything else, notice whether the light is steady or blinking: a blinking light needs attention sooner.
Here are three ways to get the codes, and what to do next.
Table of Contents
First: Is the Light Steady or Blinking?
| Light | What it generally means | What to do |
|---|---|---|
| Steady | A fault has been detected | Check the codes soon and plan a repair |
| Blinking | A more severe malfunction | Reduce driving and get it checked promptly |
The California Air Resources Board notes that certain malfunctions can cause the warning light to blink, and that many manufacturers recommend having the vehicle serviced as soon as possible in that case, because some faults can damage the catalytic converter.
If the car is overheating, losing power, or running roughly, pull over safely and get help.
Way 1: Use Your Own OBD2 Scanner
- Find the 16-pin OBD2 port under the dashboard, usually near the steering column.
- Plug in the scanner with the car off.
- Turn the ignition on, or start the engine if the scanner’s instructions say to.
- Select Read Codes and write down every code.
- Look up each code using the scanner’s definitions or a reliable repair source.
Owning a scanner means you can check codes any time, confirm repairs, and check emissions readiness. See how to use an OBD2 scanner for the full process.
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Way 2: Use a Bluetooth Scanner and Phone App
A small Bluetooth adapter plugs into the port and sends codes to an app on your phone. Many apps explain codes in plain language and suggest likely causes. Some features may require a subscription, so check before you buy.
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Way 3: Get a Free Scan at an Auto Parts Store
Some auto parts chains, such as AutoZone, advertise free check engine light code reading. Call ahead to confirm the service at your local store. Ask for a printout or photo of the codes, not just a part recommendation.
What to Do After You Have the Code
- Write down every code, including pending ones.
- Look up the meaning. Codes start with P, B, C, or U. Our guide on how to use a car code reader explains how to decode them.
- Check the simple things first. EVAP codes, for example, can sometimes be caused by a loose or damaged fuel cap.
- Decide on the repair. Some fixes are DIY-friendly; others need a professional diagnosis.
- Clear the code after repairing, then watch whether it returns.
Common Reasons the Check Engine Light Comes On
- Loose or faulty fuel cap (EVAP codes)
- Oxygen sensor faults
- Engine misfires from spark plugs or ignition coils
- Mass airflow sensor issues
- Catalytic converter efficiency codes
These are general patterns. The right fix depends on your vehicle and the exact code.
Frequently Asked Questions
Can I drive with the check engine light on?
If it’s steady and the car drives normally, you can usually drive carefully while you arrange a diagnosis. If it’s blinking or the car runs poorly, reduce driving and get it checked promptly.
Can I check codes without a scanner?
Some vehicles can display codes through the instrument cluster, but methods vary by make and model and aren’t universal. A scanner or a free parts-store scan is the most reliable option.
Will disconnecting the battery clear the check engine light?
It may clear codes on some vehicles, but it doesn’t fix the problem and can reset other settings. Using a scanner is a better way to clear codes after a repair.
Why did my check engine light turn off by itself?
Some faults are intermittent. If the condition stops, the car may turn off the light after several drive cycles, but the code may remain stored.
The Takeaway
Checking your check engine light codes is easy with a scanner, a Bluetooth app, or a free parts-store scan. Note whether the light is blinking, record the codes, and use them as a starting point for diagnosis, not a final verdict.
For scanner recommendations, see our list of the best OBD2 scanners.
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