A member of our review team toggles through the menu of an OBD2 scanner.

Learning how to use an OBD2 scanner can benefit any car owner even if they aren’t an auto repair expert. While OBD2 scanners offer a wide range of functions – some of which are best left to professional mechanics – even non-mechanics can easily use a basic OBD2 scan tool to:

  • Check engine fault codes
  • Run emissions diagnostics

A simple OBD2 code reader that will perform both of these functions can be purchased for around $60. Check engine lights can indicate a range of issues, from a loose gas cap to a busted catalytic converter. When your check engine light comes on, an OBD2 scan tool can determine precisely what’s going on. Determining the issue yourself allows you to decide if you need to take your vehicle to the mechanic.

Another useful and easy-to-use OBD2 scanner feature is emissions system testing. It’s worth running a basic emissions test before an inspection. If there’s an issue with your emissions system, you can address it and save yourself a failed inspection.

What Is An OBD2 Scanner?

A member of our review team holds up the pinbox of a scan tool that connects to an OBD2 port.

An OBD2 (or OBDII) scanner is a device that connects to a car’s onboard computer. These scanners can perform a variety of functions, including:

  • Read onboard diagnostics trouble codes (DTCs)
  • View live data about engine performance
  • View vehicle system information recorded at the time a DTC occurred (freeze-frame data)
  • Run emissions tests
  • Check the status of critical systems such as the anti-lock braking system (ABS) and the supplemental restraint system (SRS)
  • Alter engine and fuel system parameters to optimize engine performance
  • Change advanced computer settings such as the speed that your vehicle’s locks automatically engage

Not every OBD2 scanner can perform all of the functions listed above, and some may outperform others. An OBD2 scan tool will be able to perform most of these tasks, while an OBD2 code reader is much less expensive and can only read engine error codes, show live engine data, and perform emissions tests.

How To Use An OBD2 Scanner: Step-By-Step

Every OBD2 scanner is a little bit different, so it’s worth reading the user manual to learn specific information related to your car diagnostic tool. The basic steps for operating most OBD2 scanners are the same:

  1. Locate the ODB2 port
  2. Connect your OBD2 scan tool
  3. Turn your vehicle on
  4. Initiate the DTC scan
  5. Decipher the DTCs

1. Locate The ODB2 Port

A close-up of an OBD2 port.

OBD2 ports are typically located below and to the left of the steering column. Some are tucked back pretty far, so you may need to crouch down and use a flashlight to locate yours. The OBDII port is a 16-pin, trapezoid-shaped connector.

2. Connect Your OBD2 Scan Tool

There are both wired and wireless OBD2 scanners. Connect your cord (or dongle) to the OBD2 port.

3. Turn Your Vehicle On

Some OBD2 scanners are self-powered, while others require energy from your vehicle’s battery to operate. Check your owner’s manual to determine if you should power your vehicle to use your OBD2 scanner. In most cases, you’ll need to turn your car’s power on but keep the engine off to use an OBD2 scanner.

Many OBD2 scanners will automatically detect your vehicle information, but some may require you to enter this information yourself. You could be asked to simply input your vehicle’s year, make, and model, or you may need to provide your vehicle identification number (VIN). If you need to locate your VIN, it’s typically displayed on the driver’s side dashboard or a sticker inside the driver’s side door (you’ll need to open the door to see it).

4. Initiate The DTC scan

A reviewer initiates a code scan of a vehicle's engine.

Your car scanner may automatically power on when the car is powered, or you may need to press a power button. When everything is ready, locate the menu option to check diagnostic trouble codes or initiate a scan. Check your scanner’s user manual to find out how to do this if you’re having trouble. With most OBD2 scan tools, this feature shouldn’t be difficult to locate. Many have a single button that initiates DTC scans.

There are generally two types of DTC codes: active and pending. Some scanners have separate menu options for viewing each type of code.

  • Active codes are DTCs that trigger the check engine light. These represent issues that should be addressed immediately.
  • Some DTCs related to the emissions control system don’t immediately trigger the check engine light. These are minor but recurring failures and will be stored as pending codes. A pending code will become an active code and trigger the check engine light once a certain failure threshold is met.

If you’re trying to determine the cause of a check engine light, check active codes.

5. Decipher The DTCs

A diagnostic trouble code is displayed as an alphanumeric string. For example, the engine trouble code for a loose gas cap is “P0457.” The quickest way to understand the meaning of a DTC is to look it up online using a search engine. Some more advanced diagnostic scanners will decipher and explain the code for you.

The first letter in a DTC can be P, B, C, or U. This letter indicates what part of your vehicle has an issue.

  • P: Indicates an issue with the powertrain (the engine, transmission, and fuel system)
  • B: Indicates an issue with the body (cabin interior parts such as the steering system, airbags, and seatbelts)
  • C: Indicates an issue with the chassis (components underneath the car such as the axles, ABS, wheels, and power steering)
  • U: Indicates a network issue (wiring)

Some diagnostic trouble codes are universal, while others are manufacturer specific. The number that follows the first letter of a DTC will be either 0 or 1. A 0 indicates a universal (generic) code and a 1 indicates a manufacturer-specific code.

Most OBD2 scanners have broad compatibility with most manufacturers. If your vehicle is vintage, luxury, or built by an obscure manufacturer, research which OBD2 scanners are compatible with your car.

Emissions Testing

In addition to checking DTCs, a DIY home mechanic can use an OBD2 scanner to perform an emissions test. To do so, follow steps one through three listed above. Once your diagnostic scan tool is powered, select the emissions test menu option instead of the DTC scan.

Which OBD2 Scanner Is The Best?

The best OBD2 scanner for you depends on your budget, what you need it for, how many features you want it to have, and how long you want it to last. For those who want a basic OBD2 scan tool for DTC lookup and emissions tests, one of our recommendations is the Foxwell NT301. This scan tool costs about $70 and is very easy to use.

Another one of our picks is the BlueDriver Bluetooth Pro. It’s a little more expensive at around $120. This Bluetooth OBD2 scanner pairs with your smartphone and offers more advanced features, such as custom engine monitoring and access to a repair report database.

If you want to compare the features between even more advanced OBD2 scanners, check out our review of the best OBD2 scanners on the market today or our review of the best Bluetooth OBD2 scanners.

Why Is My Check Engine Light On?

Your vehicle’s check engine light will illuminate when the onboard computer detects a mechanical or electrical issue. The severity of this problem can range greatly. A check engine light can be the result of a loose gas cap or a significant parts malfunction. In some vehicles, the check engine light will come on automatically after a certain mileage to indicate your vehicle needs routine maintenance.

The only way to know what a check engine light indicates is to use an OBDII scanner or OBDII code reader, which will communicate with your vehicle’s computer and provide a diagnostics code that specifies the issue.

Our Review Standards

To ensure the accuracy of all the tips and information in this guide, we have our network of experts share their thoughts on OBD2 scanners. These experts have over 100 years of combined experience in the auto industry, in fields ranging from detailing to accessories to tires, and everything in-between. Interviewing experts ensures that all the information and advice we publish is as accurate as possible and delivered in a way that’s helpful and easy to understand.

Our team also combed through dozens of resources such as federal safety studies, research from reputable institutions, verified firsthand accounts, interviews and videos from credible automotive professionals, and our own prior testing conducted by our expert testing team.

Why You Can Trust Us

Since 2020, we have published over 200 auto product reviews in an effort to make owning a car and shopping for auto products easier. Our team of writers, editors, researchers, and product experts collaborates to thoroughly vet everything we publish. We try to perform in-house testing on real vehicles whenever possible before making our buying and informational guides.

When testing is not feasible, however, our aim is to make your life easier by doing all the online research for you. For more information on our testing methodology, check out our methodology page here.

OBD2 Scanner: FAQ

*Data accurate at time of publication.