Guide to Reading OBD2 Codes and What They Mean

Whenever you take your car to an auto shop for a check-up or repair, you’ll otice that mechanics usually plug in a gadget to your car’s OBD port to scan your car’s computer. That gadget is called an OBD2 scanner, which collects and reads the fault codes stored in your car’s computer.

That tool is what helps mechanics identify what and where the problem is, so they know where to check inside your car. An OBD scan is what confirms the existence of an automotive issue.

Now, the real issue is whether you should always trust their interpretation of those codes. Many repair shops, especially those that also sell parts, may sometimes mislead car owners into buying new components to make a profit.

To protect yourself and your car from such schemes, you need to learn how to read OBD2 codes. This way, you have an idea of what the real problem is.

In this guide, you will learn what OBD2 codes are and how to read them.

A list of the standard generic code categories will also be interpreted.


In learning about OBD2 codes, you’ll come across several acronyms that may be used interchangeably or in different ways.

The most important are the OBD, DTC, OBD2, and SAE.

OBD directly refers to your car’s On-Board Diagnostics (OBD) system that stores fault data in the form of Diagnostic Trouble Codes (DTC). These codes are then formatted into a coding form called OBD2, or OBD-II codes that are read through OBD scan tools.

DTC and OBD2 virtually mean the same—fault codes—so they can be freely interchanged.

SAE (Society of Automotive Engineers) codes, on the other hand, refer to generic codes within the DTC or OBD2 format. SAE is referred to as “generic” and is represented as “0” in the second digit of OBD2 codes.


The OBD2 standard coding format is comprised of five (5) digits.

Generic P Code

1. The first digit is a letter corresponding to the category or system in the car that has an issue.

There are four different systems:

  • B codes (Bxxxx) – refers to the “Body” system. B codes indicate issues that occur within the passenger compartment.
  • C codes (Cxxxx) – refers to the “Chassis” system. C codes indicate issues that occur outside the passenger compartment.
  • P codes (Pxxxx) – refers to the “Powertrain” system. P codes directly indicate issues occurring in the car’s engine compartment.
  • U codes (Uxxxx) – refers to “User network” system. U codes indicate issues regarding shared computer connectivity within the car.

2. The second digit is either 0 or 1

This is the standard, but 2 or 3 may also appear.

  • 0 – SAE or generic codes. This indicates issues that are common across all car models that use the OBD2 standard coding. For example, in a P0xxx DTC, it indicates that there is a generic issue occurring in the Powertrain system.
  • 1 – Manufacturer specific codes. This indicates issues that are specific to the car’s model or make. In a B1xxx DTC, it indicates that a manufacturer specific issue is occurring in the Body system.
  • 2 and 3 – Variable codes. These codes may refer to either generic or manufacturer specific codes, depending on the affected system.

In B codes, generic issues are indicated as B0xxx and B3xxx. Manufacturer specific issues are indicated as B1xxx and B2xxx.

In C codes, generic issues are indicated as C0xxx and C3xxx. Manufacturer specific issues are indicated as C1xxx and C2xxx.

In P codes, generic issues are indicated as P0xxx, P2xxx and P34xx – P39xx. Manufacturer specific issues are indicated as P1xxx and P30xx – P33xx.

In U codes, generic issues are indicated as U0xxx and U3xxx. Manufacturer specific issues are indicated as U1xxx and U2xxx.

3. The third digit indicates which function system is experiencing the issue.

It is usually represented in numbers (from1 to 9). In hybrids, it may be represented in letters (A to C).

  • 1 – Fuel and air metering
  • 2 – Fuel and air metering in the injector circuit
  • 3 – Ignition system and/or misfire
  • 4 – Auxiliary emission control
  • 5 – Speed control and idle control systems
  • 6 – Computer output circuit
  • 7, 8 and 9 – Transmission-related
  • A, B and C – Hybrid propulsion

4. The fourth and fifth digits refer to the exact problem in the specified systems.

It is represented in numbers (from 00 to 99). These specific fault codes are individually listed and can be downloaded from online sources.


P codes are the most common and broadly defined OBD2 codes. This is because most of the problems that need diagnosing are those that occur in the engine compartment.

P codes are also the most important to learn for any car owner.

Here’s a list of the generic P code categories and what they refer to:

  • P0100 to P0199 – These are DTCs that refer to issues in the fuel and air metering system such as the mass airflow (MAF) sensor.

    Example: P0171 (System Too Lean - Bank 1) means that the air entering your engine is too much compared to the fuel entering it.
  • P0200 to P0299 – These are DTCs referring to issues in the Injector circuit’s fuel and air metering system.
  • P0300 to P0399 – DTCs referring to misfires or problems with the ignition system.

    Example: P0301 (Cylinder 1 Misfire Detected) means that something is causing a problem in the fuel injector or spark plug in one or more cylinders.
  • P0400 to P0499 – DTCs that refer to problems with the auxiliary emission controls.

    Example: P0442 (Evaporative Emission Control System Leak Detected) means that there is a small to medium leak detected in the evap system.
  • P0500 to P0599 – These are DTCs referring to issues involving the speed control and idle control systems like the idle air control valve.
  • P0600 to P0699 – DTCs indicating faults in the computer output system.
  • P0700 to P0999 – These are DTCs related to Transmission issues in the gearbox.

This is just a collective list of the generic P Codes. To know which exact part of the affected systems is causing the problem, you need to refer to the fault codes indicated in the OBD2 code’s fourth and fifth digits.

For manufacturer specific codes, the information must be obtained from your car’s manufacturer.


Being able to read OBD2 codes provides certain advantages:

You get an idea about the need for repair or replacement.

If your car transmits an OBD2 code, it doesn’t necessarily mean that the faulty part involved needs replacing.

When you read the code and know exactly which part is affected, you can inspect that part to further diagnose the problem or have someone you trust to inspect it for you.

Reading OBD2 code to Protect Car

You get to know your car better.

Learning to read OBD2 codes will allow you to better understand your car’s capacity and current condition.

By noting the frequency and pattern of a certain issue’s occurrence, you’ll be able to determine which likely causes that problem, and prevent it in the future.


Starting with the Complete Guide, you are able to read OBD2 codes.

Getting an OBD2 scanner will help you diagnose and monitor the car's health. You can see a huge variety of OBD 2 scanner products in this review.

Also read this useful article to better understand the different types of OBD2 scanners, and how to to use it.


Learning to read your car’s OBD2 codes is like learning to read an X-ray or CT-Scan. It gives you the ability to identify problems in your car so you can determine whether you need to repair or replace faulty parts.

Once you learn this, you can save a lot of money, time and energy on your car’s maintenance and repair.

34 thoughts on “Guide to Reading OBD2 Codes and What They Mean”

  1. I wish I had thought to do this when I was younger. I wonder if I’ve been ripped off from mechanics now. They need to teach this in school! I also think it’s important to be able to know what’s going on in your car.

  2. I didn’t know what obd codes were exactly until now. I’m glad I’m able to look up what a code means if I need to. I need to get one of these scanners… my car’s check engine light has come on a couple of times.

  3. I bet a lot of mechanic’s shops don’t like it if people have this knowledge, lol. Thank you for sharing this valuable info.

  4. Wow…this is wonderful to know that an On-Board Diagnostic (OBD) scan is what confirms the existence of an automotive issue. With this, you can actually detect car troubleshooting codes with ease. Thanks for sharing this information.

  5. Wow, I know how to read car codes from my OBD2 code now, my mechanic cant just give me shit again. What each digit mean then we can solve the issue together. I cant wait to see his expression 😃😃👌

  6. Now car fault codes explained here will allow me to reduce unnecessary cost from my mechanic. I know what each digit stands for, no more scam 🤔

  7. It is a must that we understand how to read car codes. This is one of the helpful ways to more about your car.

  8. This makes sense. Particularly in today’s vehicles which are guided by computers, I learned in school that machines has a language of 0’s and 1’s. That said it is an edge if we know how to read car codes just in case or at the least have a background on it.

  9. Just learned a new one for vehicles now. car fault codes explained in a way that even a novice can understand. Thanks for this

  10. The OBD2 code has been a helpful code for automobiles. For a lasting solution on how to read car codes, this article will help you out.

  11. Though I’m yet to have a car but knowing car troubleshooting codes is very important. It will be helpful in the long run.

  12. This is the first article I’ve come across with car fault codes explained so well. I’ll have to bookmark the page and refer later.

  13. This guide is agreat help to learn how to read car codes, speacialy to avoid buying unnecesary stuff for the car.

  14. Did you just compare the obd2 code guide to reading an X ray??? Interesting but codes are numbers so I imagine it being translated first before it can be read? Reading this article makes me curious about this guide and how it benefits a vehicle.

  15. The automobile industry has grown to the use of OBD2 code. This post of obd2 code guide can be but over emphasized. I wish everyone can have access to this wonderful guide. Thanks for sharing

  16. Learning how to read obd2 codes is a must for every car owner except you want to continuously throw your Money into the moon..thanks a bunch for education us on how to read this codes..I never knew it could be this easy..thumbs up

  17. How to read obd2 codes now just got easier than I have expected. I always thought this obd2 code those not work but right now I love how wonderful it is now. Thanks for this

  18. Wow, this is a very good article… by giving a detailed explanation of how to check codes. Really a big help so that people are not misled again, so amazing! This will be a big surprise for them, lol.

  19. Thanks for outlining how to read obd2 codes. It’s definitely something worth being well versed in so you can negotiate for the right deal when getting your car repaired. It will also help you take proper care of your vehicle overtime knowing what signs or malfunctions to look for.

  20. Knowing how to check codes is one of those skills that can potentially save any car owner a lot of money. Everyone ought to learn it.

  21. This is one of the best guides on generic obd2 codes that I have come across. So happy to have found the article!

  22. Thanks for freely sharing this obd2 code guide. This will prove to be a useful resource for a great many people.

  23. Before reading this article I had no idea how to read obd2 codes. The write up really couldn’t have come at a better time for me 🙂

  24. Talks on how to read obd2 codes has been town for sometimes now. But thanks to this great and solution post. We got the best answer ñow.

  25. Thank you so much for this elaborate guide on how to check codes. I have been searching all over the internet for this information.

  26. Reading generic obd2 codes can be quite a challenge. With this guide everything is much easier though! Great write-up and keep it up 😉

  27. What a comprehensive obd2 code guide! This is so well researched and laid out. I will be referring to this whenever I need help with OBD2 codes.

  28. Anyone experiencing challenges with how to read obd2 codes should definitely read this article. There is a treasure trove of useful information here!

  29. I would really like to learn how to check codes. That way I can always diagnose my car by myself and at least save some money.

  30. I am so grateful for this obd2 code guide. If I get the scanner at least now I know where to begin and how to interpret the codes.

  31. I got a tester at Walmart for twenty dollars that tells me the same almost useless stuff and I don’t need to know how to use a smart phone. I have yet to see any information on any tester that tell me the exact component that is bad. My collector carbureted cars are simpler to fix by far and NEVER leave me stranded.


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