How to Use an OBD-II Scanner in 5 Minutes

What You Need

Any OBD-II scanner will work. Options range from a $20 Bluetooth dongle that pairs with a free app on your phone, to a $150 standalone handheld unit with a screen. For basic code reading, the cheap Bluetooth option is perfectly adequate. The most popular apps for the Bluetooth dongles are OBD Fusion, Torque Pro, and Car Scanner.

If you do not want to buy anything, most AutoZone, O'Reilly, and Advance Auto Parts locations will read codes for free with their own scanner.

Step 1: Find the OBD-II Port

The port is almost always under the dashboard on the driver's side. Look for a 16-pin trapezoid-shaped connector. On most cars it is within arm's reach of the steering wheel without needing to crouch down. Common spots: just above the pedals, under the dash near the fuse panel, or tucked into a small trim panel you can pop open with your finger.

If you are having trouble finding it, a quick search for your year, make, and model plus "OBD port location" will give you the exact spot.

Step 2: Plug In the Scanner

With the ignition off, plug the scanner into the OBD port. It should click in and seat firmly. If you are using a Bluetooth dongle, pair it with your phone now before turning the key.

Step 3: Turn the Ignition to "On"

You do not need to start the engine. Turn the key to the "On" position (the position where your dashboard lights up, also called "accessory on" or "KOEO" in shop shorthand). The scanner needs power from the car's systems, and turning the key to "On" provides it without cranking the engine.

Step 4: Read the Codes

On a handheld scanner, press the "Read" button and wait a few seconds. On a phone app, connect to the dongle and tap "Read fault codes" or similar. The scanner will show you any stored diagnostic trouble codes (DTCs).

You may see two types:

• Stored codes: Faults the ECU has confirmed and logged. These are what triggered the check engine light.
• Pending codes: Faults the ECU has seen once but not yet confirmed. The light may not be on yet, but the problem is developing.

Write down every code number. Then look each one up here to understand what it means, how serious it is, and what the likely fix is.

Step 5: Decide Whether to Clear the Code

Clearing a code erases it from the ECU's memory and turns off the check engine light. This sounds appealing, but there are two important things to know first.

First, clearing codes also resets your car's readiness monitors. Many states require these monitors to be complete for an emissions test. If you clear codes and immediately go for a test, you will fail on "incomplete monitors" even if the underlying problem is fixed. You typically need to drive 50 to 100 miles in varied conditions to re-set them.

Second, if you clear a code without fixing the problem, the light will come back. The ECU will detect the same fault on the next drive cycle. Clearing codes makes sense only after you have identified and fixed the root cause.

What the Code Format Means

Every OBD-II code follows the same pattern: one letter, four digits.

• The letter tells you the system: P for powertrain, B for body, C for chassis, U for network.
• The first digit tells you whether it is a generic code (0) or manufacturer-specific (1, 2, or 3).
• The remaining three digits identify the specific fault.

Generic codes (P0xxx, B0xxx, etc.) are standardized across all makes. Manufacturer codes (P1xxx) vary by brand. Our database covers both, so you can look up any code you find regardless of the car.