How to Read Code on Car

advance auto code reader

You are probably tired of running to your mechanic every time your car shows the check engine light. It not only consumes your time, but you must also pay them to scan your vehicle and find the problem. You later wonder whether it’s necessary to endure so much stress, yet you can do that at home with your own OBD2 scanner.

However, do you know how to read the codes? It would be a waste to have an OBD2 code reader, yet you can’t interpret the codes it shares with you. Here, you’re about to learn how to read codes and use them to know the issues in your car.

What’s an OBD2 Code?

If your car was manufactured post-1996, it comes with a Second-Generation On-Board Diagnostics system, otherwise known as the OBD2. Car manufacturers agreed to a universal system for diagnostic codes. They all have a standard connector that allows you to plug in the code reader and access your vehicle information. A code is a set of letters and numbers representing a particular problem in your car.

The OBD2 is a computer with a network of sensors from different parts of the vehicle connected to it. When something happens to your car’s components, their respective sensors send that information to the computer. That info is known as the freeze frame data. The data is stored in the computer until the code is repaired and cleared.

How Do You Read the Codes?

Reading the codes requires an OBD2 scanner. Ancel’s scanners for DIYers cost between $27.99 and $59.99. Most of their scanners come with a wear-tear-resistant cable, while one is a Bluetooth-powered module that you can connect to your smartphone. Here are the steps to follow when reading codes.

Step 1: Plug the OBD2 Scanner

Your OBD2 has a 16-pin connector that goes into the vehicle’s port. Every car has a different location for the OBD port. Most of them have it under the dash or the steering wheel. If you don’t know where your car’s is, check online. You can also check your owner’s manual. In rare cases, it can be below the glove compartment.

Step 2:  Turn the Ignition On

Grab your keys, insert them in the ignition, and turn it on. Don’t start the engine. You should only turn the power on. Your OBD2 computer will activate, and your scanner will begin communicating with it. Your scanner will show you on the screen that it’s establishing a connection. If that doesn’t happen, you probably didn’t plug the scanner in well.

Another reason why your scanner might not light up could be because the OBD2 itself is damaged. One way to know whether that’s the case is by checking whether there’s power from the auxiliary power outlet (cigarette lighter). The OBD2 system and cigarette lighter share a circuit; something could be wrong if the latter is not hot!

Step 3. Enter the Vehicle Identification Number

Let’s assume the scanner is turned on and everything is going well. The next step would be to enter your vehicle's VIN. Some scanners will require you to enter the information manually, while the expensive ones will automatically detect your car’s VIN.

Before proceeding, you may also be required to enter your car's make, model, and engine type. The reason why some scanners want all this information is that some codes are manufacturer-specific. The scanner must give you more accurate information about your specific car.

Step 4: Find the OBD Codes in the Menu

The scanner will pull all the trouble codes saved on the ECU system. You can find the codes on your hand-held scanner’s screen by scrolling through the menu. If you are using a Bluetooth module connected to your phone, open the respective app, and the codes will be displayed.

The menu will provide two code sections, "codes” or “trouble codes.” You’ll be requested to choose between Pending Codes and Active Codes. All the issues causing the check engine light are Active Codes. Pending codes, on the other hand, are those codes that have happened only once but not triggered the check engine light. If they happen for the second time, they’ll trigger the check engine light.

Step 5: Record the Trouble Codes

Record the codes in the order they are displayed. You must follow the order to ensure you don’t mix up the trouble codes and fix sections with no problems.

The order of the trouble codes is displayed in the order they should be diagnosed and fixed. If you fix the first trouble code, it will resolve the next codes following the same order. It can’t happen vice versa.

Step 6: Interpret the Codes

At this point, you have recorded the codes in the correct order as they appeared on the screen. The code consists of five characters, and each one has a meaning. The first character is a letter specifying the car's area with a problem. P stands for powertrain, C for chassis such as brakes, B for the body, and U refers to the car’s communication system. P is the most common because it’s where the engine is represented.

The second character in the code is a digit between 0 and 9, which lets you know whether the problem is manufacturer-related or generic. Generic codes happen to every car, while manufacturer only happens to your specific model. Codes P0, P2, P34-P39, B0, B3, C0, C3, U0, and U3 are generic-specific. P1, P30-P33, B1, B2, C1, C2, U1, and U2 are manufacturer-specific.

Finally, we have the last two numbers. The numbers are precise, and you can find what they mean on the internet, the app, or a code book. The third code, however, has a different meaning depending on the first two characters we mentioned above.

For instance, if it’s P11, it means a manufacturer’s powertrain issue with fuel or air monitoring. P12 means the manufacturer’s powertrain has a problem with power or injection, and so forth. The last digit indicates the nature of the problem. This is where the internet becomes your friend. You can also check on the Ancel app to find the real problem.


Reading codes is simple if you have a resource where you can interpret the codes. All you need is an OBD2 scanner that can pull those codes. Whether you are looking for a Bluetooth-enabled or wired scanner, we got you covered. Visit our website and find a scanner that meets your needs.

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