Understanding OBD2 Protocols: A Deep Dive into CAN, KWP, and More

by Garage Pro September 4, 2024

As modern vehicles become more advanced, understanding how they communicate internally is essential for both professional mechanics and DIY enthusiasts. The OBD2 (On-Board Diagnostics II) system is a universal standard that allows you to diagnose vehicle issues, but what many people don’t realize is that there are different OBD2 protocols in use. Each of these protocols has a unique method of communication, and knowing which one your car uses is key to effective diagnostics.

In this article, we’ll dive into the most common OBD2 protocols, with a special focus on CAN (Controller Area Network) and KWP (Keyword Protocol 2000). We’ll also touch on older protocols like SAE J1850 and ISO 9141-2, to give you a complete understanding of how OBD2 systems function.

OBD2 scanner connected to a car, displaying diagnostic codes, with a focus on the scanner and the vehicle's interior.

The Importance of OBD2 Protocols

Before jumping into specific protocols, it’s essential to understand what OBD2 protocols actually do. OBD2 protocols are communication standards that dictate how information flows between a vehicle's ECU (Engine Control Unit) and the OBD2 scanner. Depending on the vehicle’s make and model, it will use one of these protocols to communicate data such as fault codes and sensor readings.

Having a scanner that supports the right protocol is critical to obtaining accurate information. If your scanner isn’t compatible with your vehicle’s protocol, you may not be able to read any data, rendering the scanner ineffective.

CAN (Controller Area Network)

The Controller Area Network (CAN) protocol is the most widely used OBD2 protocol in modern vehicles. Introduced in the mid-2000s, it quickly became the standard for most automakers due to its high speed and reliability. CAN is a robust, multi-master protocol that allows different electronic control units (ECUs) in the vehicle to communicate with each other without a central computer. This is especially useful in today’s cars, which have dozens of sensors and control units.

CAN operates on two dedicated communication lines: CAN-High and CAN-Low, which work together to ensure that data transmission is both fast and reliable. CAN’s speed is particularly beneficial for real-time diagnostics and for capturing rapidly changing sensor data. If you’re working with any vehicle from 2008 or later, chances are it uses the CAN protocol.

Chart displaying OBD2 protocols like CAN, KWP2000, ISO 9141-2, SAE J1850 PWM, and SAE J1850 VPW, comparing data transfer rates, communication methods, and compatibility with different vehicle types.

How CAN Impacts Diagnostics

For DIY mechanics, understanding CAN is crucial. It means that your OBD2 scanner must support this protocol to provide fast and accurate diagnostics. Most high-quality OBD2 scanners, such as the ones available at GaragePro Shop, support CAN and offer real-time data streams, making it easier to detect intermittent issues.

KWP (Keyword Protocol 2000)

The Keyword Protocol 2000 (KWP2000) is another commonly used OBD2 protocol, especially in European and Asian vehicles. KWP2000 was widely adopted before CAN became the dominant protocol and is still found in many cars built in the early 2000s. While not as fast as CAN, KWP2000 offers reliable diagnostics and supports both asynchronous and synchronous communication, depending on the vehicle’s system architecture.

KWP2000 operates over a single wire and uses an initialization process that takes a bit longer compared to CAN. Despite this, KWP2000 remains popular because of its flexibility and ease of implementation, particularly in older models. This protocol allows for advanced diagnostic functions, including ECU reprogramming in some cases.

How KWP Affects OBD2 Scanning

If you’re dealing with older cars, especially from brands like Volkswagen, Audi, or Toyota, your vehicle may use KWP2000. Ensure that your OBD2 scanner supports this protocol to avoid connectivity issues. Many OBD2 scanners available today support both CAN and KWP, making them versatile for diagnosing a wider range of vehicles.

Other OBD2 Protocols

In addition to CAN and KWP, there are several other OBD2 protocols, primarily used in older vehicles:

ISO 9141-2: Primarily used in Chrysler, European, and Asian vehicles before 2008. It operates at a slower speed and relies on a single wire for communication.
SAE J1850 PWM: Used mainly in Ford vehicles. It operates with two wires and supports a 41.6 kbps data rate.
SAE J1850 VPW: Used primarily in General Motors (GM) vehicles. It uses a single wire and offers a data rate of 10.4 kbps.

While these protocols are less common today, it’s still important to be aware of them, especially if you’re working with vehicles built before the mid-2000s.

Choosing an OBD2 Scanner That Supports Multiple Protocols

When shopping for an OBD2 scanner, you’ll want to ensure it supports multiple protocols to cover a wide range of vehicles. Most modern scanners support all major protocols, including CAN, KWP2000, and older systems like ISO 9141-2 and SAE J1850. At GaragePro Shop, we offer scanners that are compatible with all these protocols, ensuring you can diagnose nearly any vehicle with ease.

Conclusion

Understanding OBD2 protocols is key to making sure you get the most out of your diagnostics. Whether you're working on a newer car that uses CAN or an older model running KWP or ISO 9141-2, having the right OBD2 scanner for the job is essential. Be sure to check your vehicle’s manual to see which protocol it uses, and choose a scanner that supports it for accurate and efficient diagnostics.