How to Use an OBD2 Scanner (Step-by-Step for Beginners)

Step 1: Find the OBD2 Port

The OBD2 port is usually located under the dashboard on the driver's side. It is a small trapezoid-shaped connector.

• Most cars built after 1996 have an OBD2 port
• It is typically near the steering wheel
• You usually don't need tools to access it

Tip: If you can't find the port, check under the dash or near the center console.

Step 2: Plug the Scanner Into the Port

Once you find the port, plug the scanner into it. The scanner will usually power on automatically.

Depending on the scanner type, you may either:

• Use the scanner screen directly (wired scanner)
• Connect it to a phone app (Bluetooth scanner)

Not sure which type is easier? Read our guide: Bluetooth vs Wired OBD2 Scanners .

Step 3: Turn the Ignition On

Turn the car key to the "ON" position without starting the engine (or press the start button without pressing the brake).

This powers the car's computer so the scanner can communicate with it.

Step 4: Read and Save the Trouble Codes

Use the scanner menu or phone app to select Read Codes or Diagnostics.

The scanner may show codes such as:

• P0300 – Random or multiple cylinder misfire
• P0420 – Catalyst efficiency problem
• P0171 – System too lean
• P0456 – Small EVAP system leak detected

Before you press Erase Codes or Clear Codes, save the information your scanner gives you.

At minimum, write down:

• the exact trouble code, such as P0300 or P0171
• whether the code is pending, stored, or permanent
• any freeze-frame information available for the code

Your scanner may label codes as pending, stored, or permanent. If you are not sure what those labels mean, read Pending vs Stored vs Permanent Codes before clearing anything.

A pending code may appear before the check engine light stays on, while a permanent code may remain after a repair until the vehicle completes enough drive cycles.

Not sure what your code means? Browse common OBD2 trouble codes for beginners and find a simple explanation of what your car is trying to tell you.

Step 5: Understand What the Code Actually Tells You

A trouble code is a starting point for diagnosis. It does not automatically tell you which part has failed.

For example, a misfire code does not automatically mean the spark plug is bad, and a lean code does not automatically mean the oxygen sensor needs to be replaced. Several different problems can trigger the same code.

Start by looking up the exact code, then compare the common causes with the symptoms your car is actually showing.

Use freeze frame and live data for extra context

If your scanner supports Freeze Frame, check it before clearing the code. It can show information such as engine speed, coolant temperature, vehicle speed, or engine load around the time the fault was recorded.

Live Data shows what sensors and systems are reporting right now. Many live-data checks are most useful with the engine running, so keep the car safely parked and follow the instructions for your scanner or app.

As a beginner, you do not need to understand every live-data value. The goal is simply to keep useful diagnostic context instead of treating the code as the name of a part that must be replaced.

If your check engine light is currently on, read this guide first: What Does the Check Engine Light Mean?

Step 6: Decide What to Do Next

After you have saved the code and any useful diagnostic information, work through the problem in this order:

1. Look up the exact code and its common causes.
2. Check simple or visible problems first.
3. Compare the code with the symptoms your car is showing.
4. Use freeze-frame or live-data information when it helps narrow down the cause.
5. Repair the problem yourself if it is simple, or get professional diagnosis if needed.

Sometimes the issue is minor, but sometimes it requires professional repair.

If you're wondering whether it's safe to drive, see this guide: Can I drive with the check engine light on?

Common Beginner Mistakes

Clearing the code before saving the information

Save the exact code, its status, and any available freeze-frame information first. Clearing the code too early can remove useful clues that may help you or a mechanic diagnose the problem.

Ignoring a blinking check engine light

A blinking light usually indicates a misfire that could damage the catalytic converter.

Buying a very cheap scanner

Ultra-cheap scanners often have connection problems or poor code explanations.

Frequently Asked Questions

Do you need to start the engine when using an OBD2 scanner?

For reading stored trouble codes, usually not. In most cases you can turn the ignition to the ON position without starting the engine. For live data, many readings are most useful with the engine running, so follow the instructions for your scanner or app.

Can an OBD2 scanner turn off the check engine light?

Yes. Most scanners allow you to clear diagnostic trouble codes, which turns off the check engine light. However, the light may return if the underlying problem is not fixed.

Should I clear OBD2 codes after reading them?

Not immediately. Save the exact codes, their status, and any available freeze-frame information first. Clear the codes after the cause has been repaired, or when a diagnostic procedure specifically requires it. Clearing codes can also reset emissions readiness monitors.

Is it safe to drive after reading an OBD2 code?

It depends on the code. Minor issues may allow you to continue driving, but serious engine or misfire codes should be inspected as soon as possible.