Discovering the code for your check engine light doesn’t require a mechanic. With basic tools and clear steps, you can read diagnostic trouble codes (DTCs) yourself. This guide shows you how to do it safely and effectively using OBD2 scanners, mobile apps, or even your car’s built-in system.
Key Takeaways
- Use an OBD2 scanner: Most modern cars (1996 and newer) support OBD2 systems, allowing you to plug in a scanner and read codes easily.
- Locate the OBD2 port: It’s usually under the dashboard near the steering wheel—look for a 16-pin connector.
- Turn the ignition on (not the engine): This powers the scanner and vehicle computer without starting the motor.
- Read and interpret codes: Codes like P0300 mean random misfires—use online databases or manuals to understand what they mean.
- Clear codes after repair: Once fixed, use the scanner to reset the check engine light and confirm the issue is resolved.
- Try a smartphone app: Bluetooth OBD2 adapters let you view codes on your phone using apps like Torque or OBD Fusion.
- Know when to see a mechanic: If the light flashes or codes point to serious issues, get professional help immediately.
How to Find Out Code for Check Engine Light
Seeing the check engine light pop up on your dashboard can be stressful. But don’t panic—this warning doesn’t always mean a major repair. In many cases, it’s something simple like a loose gas cap or a minor sensor issue. The key to solving the problem quickly is knowing how to find out the code for the check engine light. Once you have the code, you can research what it means and decide whether to fix it yourself or visit a mechanic.
In this guide, you’ll learn step-by-step how to read diagnostic trouble codes (DTCs) from your car’s onboard computer. Whether you’re using a handheld OBD2 scanner, a smartphone app, or even your car’s built-in system, we’ll walk you through each method. You’ll also learn how to interpret the codes, clear them after repairs, and know when it’s time to call in a professional.
What Is a Check Engine Light Code?
Visual guide about How to Find Out Code for Check Engine Light
Image source: mechanicbase.com
When your car’s computer detects a problem, it stores a diagnostic trouble code (DTC). These codes are five characters long—like P0420 or P0171—and follow a standard format. The first letter tells you the system involved (P for powertrain, B for body, C for chassis, U for network). The next digit shows if it’s a generic (0) or manufacturer-specific (1) code. The last three digits point to the exact issue.
For example, P0300 means “random/multiple cylinder misfire detected.” This tells you the engine isn’t firing properly, but not which cylinder. Knowing this code helps you focus your troubleshooting.
Tools You’ll Need
Before you begin, gather the right tools. Here’s what you’ll need:
- OBD2 scanner: A handheld device that plugs into your car’s diagnostic port. Basic models cost $20–$50 and display codes clearly.
- Bluetooth OBD2 adapter: A small dongle that connects to your phone via Bluetooth. Great for using apps like Torque (Android) or OBD Fusion (iOS).
- Smartphone or tablet: Required if using a Bluetooth adapter.
- Owner’s manual: Helps locate the OBD2 port and understand basic systems.
- Notepad and pen: To write down codes and notes.
You don’t need advanced mechanical skills—just a willingness to follow steps carefully.
Step 1: Locate the OBD2 Port
The OBD2 (On-Board Diagnostics, version 2) port is where you’ll plug in your scanner. It’s required in all cars sold in the U.S. from 1996 onward.
Where to Find It
The port is usually under the dashboard, near the steering column. Look for a 16-pin connector—it’s trapezoid-shaped and may be covered by a small flap. Common locations include:
- Below the steering wheel, near the driver’s knees
- Inside the center console (lift the armrest)
- Behind a panel near the fuse box
If you can’t find it, check your owner’s manual or search online for your car’s make and model.
Tip: Make Sure the Car Is Off
Before plugging in the scanner, ensure the ignition is off. This prevents electrical issues and protects the scanner.
Step 2: Plug In the OBD2 Scanner
Once you’ve found the port, plug in your scanner. It should fit snugly—don’t force it. Most scanners have a label like “OBD2” or “DLC” (Data Link Connector).
Turn the Ignition On
Turn the key to the “ON” position—but don’t start the engine. You’ll see dashboard lights come on, including the check engine light. This powers the car’s computer and allows the scanner to communicate with it.
Wait for the Scanner to Connect
Give the scanner 10–30 seconds to boot up and connect. You’ll usually see a message like “Searching…” or “Connected.” If it doesn’t connect, check that the ignition is on and the scanner is fully inserted.
Step 3: Read the Check Engine Light Code
Now it’s time to retrieve the code.
Press the “Read” or “Scan” Button
Most scanners have a button labeled “Read,” “Scan,” or “DTC.” Press it, and the device will communicate with the car’s computer.
View the Code
The scanner will display one or more codes. Write them down exactly as shown. For example:
- P0420 – Catalyst system efficiency below threshold
- P0171 – System too lean (Bank 1)
- P0302 – Cylinder 2 misfire detected
Some scanners also show a brief description. If not, you’ll need to look it up.
Check for Pending or Permanent Codes
Some scanners show “pending” codes—issues the computer suspects but hasn’t confirmed. These may clear on their own. “Permanent” codes won’t go away until the problem is fixed.
Step 4: Interpret the Code
Now that you have the code, what does it mean?
Use Online Code Databases
Search for your code on trusted sites like:
- OBD-Codes.com
- RepairPal.com
- Your car manufacturer’s website
These sites explain what the code means, possible causes, and repair suggestions.
Example: P0420
This code often means the catalytic converter isn’t working efficiently. Causes can include:
- A failing catalytic converter
- Oxygen sensor issues
- Exhaust leaks
- Engine misfires
Not all P0420 codes require a new catalytic converter—sometimes a simple fix like replacing an O2 sensor solves it.
Use Your Scanner’s Built-In Help
Many modern scanners include a code library. Press “Help” or “Info” after reading a code to see a description.
Alternative Method: Use a Smartphone App
If you prefer using your phone, a Bluetooth OBD2 adapter is a great option.
Step 1: Buy a Bluetooth Adapter
Popular models include the BAFX Products Bluetooth OBD2 Scanner or the Veepeak OBDCheck. They cost around $20–$35.
Step 2: Pair with Your Phone
Turn on Bluetooth on your phone, plug in the adapter, and turn the ignition on. Open your OBD app (like Torque for Android or OBD Fusion for iOS) and follow the pairing instructions.
Step 3: Read Codes in the App
The app will show live data, stored codes, and even graph sensor readings. You can save codes, clear them, and even share reports with mechanics.
Tip: Keep Your Phone Charged
Using Bluetooth and apps drains battery. Keep a car charger handy.
Older Cars: Use the “Key Dance” Method (Limited Use)
Some older vehicles (pre-1996) don’t have OBD2 ports. In rare cases, you can read codes using the “key dance” method—turning the ignition on and off in a pattern to make the check engine light flash.
How It Works
For example, on some Honda models:
- Turn the ignition to “ON” (don’t start).
- Wait 2 seconds.
- Turn to “OFF.”
- Wait 2 seconds.
- Repeat 3 times.
- The check engine light will flash—count the flashes to get the code.
This method is outdated and not reliable for most modern cars. Use an OBD2 scanner instead.
Step 5: Clear the Code (After Repair)
Once you’ve fixed the issue, clear the code to turn off the check engine light.
Use the Scanner’s “Clear” Button
Most scanners have a “Clear DTCs” or “Erase Codes” option. Select it, and the light should turn off.
Wait and Test Drive
After clearing, drive the car for 20–30 minutes. The computer needs time to recheck systems. If the light comes back, the problem isn’t fully fixed.
Don’t Clear Codes Without Fixing the Issue
Clearing a code without repairing the problem is like turning off a fire alarm while the house burns. The light will return, and you could miss a serious issue.
Troubleshooting Common Problems
Scanner Won’t Connect
- Check that the ignition is on.
- Ensure the scanner is fully plugged in.
- Try a different scanner or port.
- Some cars require the engine to be running—check your manual.
No Codes Found, But Light Is On
This is rare but possible. The light might be on due to a recent repair or battery disconnect. Drive the car for a few days—sometimes the light turns off on its own.
Multiple Codes Appear
Start with the most critical ones (like misfires or fuel system issues). Some codes are “downstream” effects—fix the root cause, and others may clear.
When to See a Mechanic
While many codes can be handled at home, some require professional help.
- Flashing check engine light: This means a severe misfire that can damage the catalytic converter. Pull over and call a tow truck.
- Codes related to transmission, ABS, or airbags: These systems are complex and safety-critical.
- You’re unsure of the repair: If a code points to internal engine damage, get a professional diagnosis.
Final Tips for Success
- Always write down codes before clearing them.
- Use a code lookup tool to understand the issue.
- Keep your scanner or adapter in the car for emergencies.
- Regular maintenance can prevent many check engine light issues.
Conclusion
Finding out the code for your check engine light is easier than you think. With an OBD2 scanner or smartphone app, you can read diagnostic trouble codes in minutes—no mechanic required. Understanding these codes helps you make informed decisions, save money, and keep your car running smoothly.
Start by locating the OBD2 port, plugging in your scanner, and reading the code. Then, use online resources to interpret it and take action. Whether you fix it yourself or visit a shop, you’ll be better prepared.
Don’t let the check engine light intimidate you. With the right tools and knowledge, you’re in control.