OBD-II Scanner: How To Use Diagnostic Car Code Reader?

Nothing can throw off your day faster than a “Check Engine” light popping up on your dash. You’re wondering whether to stop and park your vehicle or drive straight to a store. Diagnose car problems without going to a mechanic with a car code reader. Just connect it to the car’s computer system and then interpret the error code display.

An engine code reader/scanner can help you make the drive/don’t drive decision and even fix the problem. It works by connecting to the car’s computer system and displaying an “error code”.

It’s worth buying an engine code reader/scanner if you’re a fairly competent amateur mechanic who understands how an engine works. But it’s not a magic bullet that always tells you exactly what’s wrong. A car code reader gives you a head start, but you still need to do some detective work before you start pulling and replacing parts (more on that later).

The cheapest car code readers are basic car code readers that throw up an alphanumeric error code but have no information on what it means. You will need to look up the code in a reference book or search the internet.

Mispriced devices actually display the issue on-screen like “P0115 Engine Coolant Temperature Circuit Malfunction”. One model even accesses the internet so you can upload the error code to a website that has information on the most likely cause of the problem.

But if you’re a real fat monkey, opt for a more expensive scanner. A scanner gives you “live” information in real-time, so you see the same data your car’s computer sees. That saves you the hassle of driving under the hood (with a schematic in hand), piercing wires, and taking sensor readings.

How To Use Diagnostic Car Code Reader

Reading and scanning car codes sounds easy, right? Well, there’s more to it than that. A code that says your oxygen sensor is “lean” could mean the sensor is dead, or it could mean the air/fuel mixture is really lean and you either have a vacuum leak or a fuel problem. How do you know? Here are three ways to get to the root of a problem without replacing our good parts.

  1. Go to the car code reader/scan tool manufacturer’s website to see if they have information about your trouble code.
  2. Use internet forums. Just search for your car model and add “forum” to the search term. Register for the site (usually free) and ask your question, including your vehicle’s year, mileage, code number and what you’ve done so far. You will be surprised by the number and quality of the answers.
  3. Subscribe to an online store guide. Not only does it contain all of the carmaker’s technical service bulletins, but it also contains the complete diagnostic procedure for your particular code. It walks you through the testing procedure, telling you which wires to check and what voltages to see. The services also include component locators to help you locate the part in your vehicle and wiring diagrams showing the connector location for each wire.

How to Use an OBD2 Scanner?

#1. Choose an OBD2 Scanner

Many different options are available including Bluetooth OBD2 scanner models. The scanners plug into the car or connect via Bluetooth to display the diagnostic code on the screen. This makes it easy to see what problems exist or what type of maintenance the vehicle requires.

If your car or truck was manufactured in 1996 or later, an OBD2 scanner is compatible. If the vehicle is older than 1996 an OBD1 scanner may work, but these are more specific to each car model.

#2. Connect Your Scanner to the DLC

Every car manufactured after 1996 has a Diagnostic Link Connector (DLC). This 16-pin connector is typically located on the left side of the driver’s dash near the steering column. Often there is a door or flap covering the port. If in doubt, the owner’s manual will provide the exact location of the DLC in your vehicle.

With the car off, insert the end of the OBD2 scan tool into the DLC. Next, put the car in an idle mode without turning on the engine. This initiates communication between the DLC and the scanner. You should see a message indicating that the information is being transferred or a connection is being established.

#3. Input the Vehicle VIN and Access the Menu

Every vehicle has an identification number (VIN). Some scanner models ask you to enter the VIN before it provides codes. If this is required, you can usually find the VIN on a sticker near the driver’s door. Next, make your way to the menu screen. The menu allows you to pick between the different systems in the car.

When you select a system, the scanner will display both active codes and pending codes. Active codes are those that trigger the check engine light. Pending codes indicate the failure of an emission control system. Repeated pending codes can turn into active codes when the same issue occurs two consecutive times.

#4. Identify and Understand the Codes

As you work your way through the codes, it’s important to understand the different letters and numbers displayed. Every code will start with a letter followed by a series of numbers. The lead letter will be one of the following:

  • P: Powertrain – The engine, transmission, ignition, emissions and fuel system are all included in this category.
  • B: Body – This can include airbags, power steering and seatbelts.
  • C: ChassisAxels, brake fluid and anti-lock braking system (ABS) are a few of the systems included under the chassis code.
  • U: Undefined – Anything that doesn’t fall under the categories above.

After the letter, you’ll see a series of numbers. The scanner may show a single code or a number of codes. Once the codes are displayed, write them down, turn off the car and unplug the scanner. For help understanding how to read live data from OBD2 scanners, refer to the user manual. It should identify the different codes and what they mean.

The fact that a code shows up doesn’t necessarily mean an immediate repair is needed. Research the individual codes thoroughly before jumping into repairs. When in doubt, take the vehicle to an Automotive Service Excellence (ASE) Certified Master Technician, and make sure they have their L1 Advanced Engine Performance Diagnostic certification.

#5. Tips to Save on Costly Car Repairs

OBD2 scanners are just one of the many car diagnostic and testing tools available for at-home use. Investing in some basic shop equipment can help you tackle regular maintenance tasks and basic car repairs at home.

As with any device, make sure to refer to the owner’s manual for specific instructions on how to navigate the menu and codes on that particular model. Although the tools are all very similar, buttons and readings may vary slightly from one unit to another.

Once you’ve learned how to use an OBD2 scanner, expand your knowledge by learning how to perform basic maintenance at home. Giving your own vehicle an oil change and replacing the air filter are great ways to save on costly repairs.