Error codes: how to interpret them and troubleshoot more effectively in everyday situations

Updated on: 2026-02-01

Table of Contents

• Product Overview
• Myths and Facts
• How Fault Codes Work
• Common Fault Codes Explained
• Questions and Answers
• Final Recommendations
• About the Author

Product Overview

An OBD2 scanner is an electronic device that connects to your car's diagnostic port to read errors stored in the engine's control system. These devices range from simple Bluetooth-based readers to advanced professional diagnostic tools. A popular and affordable solution is the ELM327 Bluetooth OBD2 device, which offers wireless connectivity and is compatible with most modern cars.

These devices use a standard called OBD2, which is an international standard for car diagnostics. With an OBD2 scanner, you can quickly retrieve diagnostic trouble codes and gain a better understanding of what your car needs before visiting a mechanic. This saves both time and money by allowing you to understand the problem before taking the car to the workshop.

Myths and Facts about Fault Codes

Myth: An OBD2 scanner can repair my car automatically

Fact: An OBD2 scanner only reads codes and presents problems. It cannot repair anything itself. It is a diagnostic tool that helps you or a mechanic understand what is wrong, but the repair must be done manually.

Myth: All fault codes mean the same thing regardless of car make

Fact: While many standard codes are common, manufacturers can also define their own codes. It is therefore important to consult your car's manual or a professional diagnostician for accurate interpretation.

Myth: You need an expensive workshop device to read fault codes

Fact: Modern, affordable solutions like the Vgate Vlinker BM wireless OBD2 reader offer many of the same features as much more expensive professional systems. You can read and understand basic fault codes without investing thousands of SEK.

How Fault Codes Work in Your Car

Your car is equipped with a number of sensors and control units that constantly monitor various systems. When something is not working normally, the system registers a fault code and stores it in memory. These fault codes are numerical or alphanumeric sequences that refer to specific problems.

An OBD2 scanner connects to the car's diagnostic port, usually located under the dashboard on the driver's side. Once connected, the device can communicate with the car's control system and retrieve stored fault codes. This information is then presented on the device's screen or through a smartphone app, depending on the type of reader you are using.

There are two main types of codes: P-codes related to the engine, transmission, and emission system, and U-codes related to network communication. By understanding these codes, you can quickly identify whether it is a serious problem requiring immediate attention or something minor that can wait until the next service.

Common Fault Codes Explained

P0300 - Random Misfire

This code indicates that the engine is misfiring randomly. It can be caused by bad spark plugs, incorrect fuel, or many other factors. It is important that this is rectified quickly to avoid damage to the catalytic converter.

P0420 - Catalytic Converter Below Threshold

This fault code indicates that the catalytic converter is not working optimally. It can be caused by a worn catalytic converter, faulty lambda sensor, or other emission problems. A more expensive repair may be required.

P0128 - Coolant Thermostat Not Optimal

This may indicate that the engine's thermostat is not functioning correctly. A faulty thermostat can affect fuel consumption and engine performance. This is usually a relatively simple repair.

For more complicated diagnostic tasks, you may need something more advanced than a simple reader. For example, for certain BMW models with the E-sys system, you may need the Ethernet to OBD interface cable for BMW E-sys, which allows for more in-depth coding and diagnostics.

Questions and Answers about Fault Codes

Can I clear fault codes myself?

Yes, most OBD2 scanners have the ability to clear stored codes. However, it is often not advisable to simply clear the codes without first addressing the underlying problem. If you only clear the codes, they will often reappear if the problem is not solved. It is better to diagnose the problem first, repair it, and then clear the codes.

Which cars are compatible with OBD2 scanners?

Most cars manufactured after 1996 are compatible with the OBD2 standard and can therefore be used with standard OBD2 scanners. However, some older or specific brands may require adapter cables. For example, Mercedes owners may need a 38-pin adapter cable for Mercedes-Benz to connect their reader.

How often should I check for fault codes?

You should regularly check for fault codes, especially if the warning light comes on the dashboard. A monthly quick check can help you identify potential problems before they become serious. If you notice any change in the car's performance or behavior, it is also good to immediately check for fault codes.

What is the difference between active and stored codes?

Active codes are problems that are currently occurring, while stored codes are problems that have occurred previously but are no longer present. An active code often requires immediate attention, while stored codes can indicate intermittent problems that are difficult to diagnose.

Can an OBD2 scanner predict future problems?

An OBD2 scanner can only report problems that have already happened or are present. It cannot predict future faults. However, by regularly monitoring fault codes, you can often catch problems early before they develop into larger and more expensive issues.

Final Recommendations

Investing in an OBD2 scanner is a smart decision for all car owners. Whether you choose a simple Bluetooth device or something more advanced, you will save money in the long run by being able to diagnose problems yourself before going to a workshop.

For most users, we recommend starting with an affordable Bluetooth reader that works with your smartphone. If you need more advanced features later, you can always upgrade. For Mercedes owners or other brands with specific connection needs, make sure you have the correct adapter cable from the start.

Also remember that an OBD2 scanner is a tool for diagnosis, not repair. If you are unsure what a code means or how to fix a problem, it is always best to consult a professional mechanic. But by understanding what the codes mean, you can make a more informed decision and potentially save significant amounts on repairs.

Finally, take care of your car by staying updated on any potential problems through regular fault code checks. This is a simple but effective way to extend your car's lifespan and avoid expensive surprises on the road.

About the Author

Expert in Car Diagnostics and Fault Code Reading

I am a dedicated car enthusiast and expert in car diagnostics through OBD2 scanners. With over a decade of experience in helping car owners understand and fix their vehicles, I am passionate about making car maintenance more accessible to everyone. I believe that knowledge of fault codes and diagnostics should not be limited to professional mechanics. Through my articles and guides, I strive to give you the tools and understanding you need to take better care of your car. Feel free to contact me with questions or feedback.