OBD2 Codes: Definition, Types & How To Interpret

Do you ever feel like your car is trying to tell you something, but you’re just not sure what? Well, it turns out that it actually is! OBD2 codes are like a secret language that your car speaks, and by understanding them, you can become a master of car troubleshooting.

In this guide, we’ll explain what OBD2 codes are, how to interpret them, and how to troubleshoot the issues they indicate. 

So buckle up and get ready to learn everything you need to know about OBD2 codes!

What are OBD2 Codes?

OBD2 codes are numerical codes that represent specific problems with a vehicle’s systems. Each code consists of a combination of letters and numbers, and it represents a particular system or component in the vehicle that is experiencing a problem. For example, the P0300 code indicates a misfire in the engine’s cylinders, while the P0171 code indicates a lean condition in the fuel mixture. 

By using a code reader or diagnostic scanner, you can retrieve OBD2 codes. They are an essential tool for identifying potential issues with a vehicle. However, it’s important to note that OBD2 codes are just a starting point for diagnosing car problems, and they don’t always provide a precise diagnosis. Instead, they indicate which systems or components are experiencing issues, allowing mechanics and car owners to focus their diagnosis and repair efforts.

Note: In the Diagnostic Trouble Code Definition J2012 DEC2007, the SAE International stated that most circuit, component, or system diagnostic trouble codes that do not support a subfault strategy are specified by four basic categories: 

  • General Circuit/Open
  • Range/Performance
  • Circuit Low
  • Circuit High

Specifically, Circuit Low is measured with the external circuit, component, or system connected. The signal type (voltage, frequency, etc.) shall be included in the message after Circuit Low. Meanwhile, circuit High is measured with the external circuit, component, or system connected, and the signal type (voltage, frequency, etc.) may be included in the message after Circuit High.

2 Main Types of OBD2 Codes

Before we explore how to interpret OBD2 codes, let’s learn about the different types of codes. There are two main types of OBD2 codes: Generic OBD2 codes and Manufacturer-specific OBD2 codes. 

The diagnostic codes referred to as generic codes are those represent common problems standardized across the industry, allowing for consistency and ease of use among different manufacturers and models of vehicles. Some generic OBD2 codes are defined as ISO/SAE reserved codes. If you receive an “ISO/SAE Reserved” code on your OBD scanner, it doesn’t necessarily indicate a problem with any specific part or component of your vehicle. Instead, it indicates that either the code is reserved for future use or the system violates particular standards set by the ISO and SAE regulatory bodies.

Manufacturer-specific codes are unique diagnostic trouble codes that are specific to a certain manufacturer or model of vehicle. Unlike generic codes, these codes are designed specifically for the unique systems and components of a particular vehicle. This means that they may not be applicable to other makes and models of vehicles. Manufacturers use these codes to provide more detailed information about specific problems that may be encountered in their vehicles.

How To Interpret OBD2 Codes?

Understanding OBD2 codes is crucial for diagnosing and fixing issues in modern vehicles. These codes provide important information about specific systems and components in the vehicle that need attention.

In this section, we’ll break down the different parts of an OBD2 code and show you how to interpret and understand them.

The First Character (Letter) – Trouble Code System

The first character in an OBD2 code is a letter that represents the trouble code system. The letter can be B, C, P, or U, indicating different categories of vehicle systems:

  • B stands for Body systems, which provide functions inside the passenger compartment that provide vehicle occupants with comfort, convenience, and safety.
  • C stands for Chassis systems, which include mechanical systems outside of the passenger compartment, such as the brakes, steering, and suspension.
  • P stands for Powertrain systems, which cover functions related to the engine, transmission, and drivetrain accessories.
  • U stands for Network and Vehicle integration systems, which include functions shared among the vehicle’s computers and systems.

The Second Character (Number) – Type of Code

The second character in an OBD2 code can be a number between 0 and 3, which indicates the type of code as follows:

  • Powertrain codes:
    • ‘0’ or ‘2’: Generic 
    • ‘1’: Manufacturer-specific
    • ‘3’: P3000-P3399 manufacturer-specific; P3400-P3999 generic 
  • Network and Vehicle Integration codes:
    • ‘0’: Generic 
    • ‘1’ or ‘2’: Manufacturer-specific
    • ‘3’: Generic and manufacturer-specific
  • Body and Chassis codes:
    • ‘0’: Generic (SAE)
    • ‘1’ or ‘2’: Manufacturer-specific
    • ‘3’: Reserved for future use

The Third Character (Number/Letter) – Affected Subsystem

The third character in an OBD2 code is a number or letter, ranging from 0 to 9 or A to F, that specifies the affected subsystem as below:

0 – Fuel and air metering and auxiliary emission controls

1 – Fuel and air metering

2 – Fuel and air metering (injector circuit)

3 – Ignition systems or misfires

4 – Auxiliary emission controls

5 – Vehicle speed control and idle control systems

6 – Computer and output circuit

7, 8, 9 – Transmission

A-F – Hybrid Trouble Codes

The Fourth And Fifth Characters (Number) – Fault Description

The final part of a DTC is a two-character number or letter ranging from 00 to FF. It defines the specific related to a particular system or component in the vehicle. The specific meaning of these numbers can vary depending on the car’s manufacturer and model. However, they generally provide more detailed information about the fault detected. 

how to read obd2 codes
A quick summary on how to interpret OBD2 codes

What’s Next? Look up OBD2 Codes, OBD2 Codes List and More

At some point, every car owner will encounter an OBD2 code. But what do these codes mean, and how can you diagnose and fix issues in your vehicle? We’re here to help!

Our OBD codes lookup tool allows you to quickly search for specific OBD2 codes. Then you can get detailed information on what they mean and how to fix them. Simply type in the code and let our tool do the rest!

If you’re looking for a more comprehensive list of codes for your vehicle, check out our Code List Generator. This tool provides a complete list of OBD2 codes for your car brand, making it easy to diagnose and fix issues in your vehicle.

But OBD2 codes are just the beginning! To truly understand your vehicle’s health, it’s important to have a deeper understanding of OBD systems and how they work. Check out our OBD Knowledge category to learn more about OBD systems, scan tools, and how to diagnose and fix issues in your vehicle.

With these tools and resources at your fingertips, you can take control of your vehicle’s health and become a more informed and confident car owner. 

Thanks for reading, and we hope that this OBD2 codes guide has been helpful in empowering you to diagnose and fix issues in your vehicle. Keep up the good work, and happy driving!

Reference Source – Read more about OBD2 Codes

If you are looking for a comprehensive list of trouble codes for your vehicle’s On-Board Diagnostic (OBD) system, you may find the SAE DTC Definitions – J2012 Revised DEC2007 report to be a valuable resource. This technical report, published by SAE International, provides a standardized set of fault codes for malfunctions detected by the OBD system in passenger cars, light and medium-duty trucks.

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