The On-Board Diagnostics II (OBD2) system is crucial for modern vehicle diagnostics, allowing mechanics and car enthusiasts to read vehicle data and troubleshoot issues. A key aspect of OBD2 is the communication protocol it uses. While many sources may inflate the numbers, there are fundamentally five main OBD2 protocols that vehicles utilize. Understanding this Obd2 Protocol List is essential for anyone working with vehicle diagnostics.
OBD-II Protocol Overview
OBD2 compliant vehicles employ one of five primary communication protocols. These protocols ensure standardized communication between diagnostic tools and the vehicle’s computer. It’s important to distinguish between true communication protocols and protocol variants, as some may mistakenly list variants as separate protocols, leading to inflated counts. Tools like ELM-USB and OBDTester are designed to support all of these standard protocols.
ISO 15765-4 (CAN-BUS)
CAN-BUS (Controller Area Network) is the most modern and prevalent OBD2 protocol, mandated for all vehicles sold in the US from 2008 onwards. It uses pins 6 and 14 on the OBD2 connector for communication, employing differential signaling. While there are four ISO 15765-4 variants, they mainly differ in identifier length and communication speed:
- ISO 15765-4 CAN (11 bit ID, 500 Kbaud)
- ISO 15765-4 CAN (29 bit ID, 500 Kbaud)
- ISO 15765-4 CAN (11 bit ID, 250 Kbaud)
- ISO 15765-4 CAN (29 bit ID, 250 Kbaud)
It’s worth noting that some manufacturers, like Fiat, Alfa, and Lancia, have used a fault-tolerant CAN-BUS at 50 kbaud, which is not compatible with the standard OBD2 protocols.
ISO 14230-4 (KWP2000)
KWP2000 (Keyword Protocol 2000) was a very common protocol, particularly in vehicles from 2003 onwards that used the ISO9141 K-Line. It communicates via pin 7 of the OBD2 connector. The two variants of ISO 14230-4 differ primarily in their communication initialization methods, but both operate at 10400 bits per second:
- ISO 14230-4 KWP (5 baud init, 10.4 Kbaud)
- ISO 14230-4 KWP (fast init, 10.4 Kbaud)
ISO 9141-2
This is an older protocol primarily found in European vehicles manufactured between 2000 and 2004. ISO 9141-2 utilizes pin 7 and optionally pin 15 for communication.
SAE J1850 VPW
SAE J1850 VPW (Variable Pulse Width Modulation) is a diagnostic protocol mainly used in General Motors (GM) vehicles. It uses pin 1 of the OBD2 connector, and its communication speed is 10.4 kilobytes per second.
SAE J1850 PWM
SAE J1850 PWM (Pulse Width Modulation) is another diagnostic protocol, primarily used in Ford vehicles. It utilizes pins 1 and 2 for differential signal communication at a rate of 41.6 kilobytes per second.
Determining Protocol from OBD2 Connector Pinout
In many cases, you can identify the OBD2 protocol used by a vehicle by examining the pinout of its OBD-II connector. The presence or absence of pins in specific locations can indicate the protocol. Refer to the table below for a general guideline:
| Standard | Pin 2 | Pin 6 | Pin 7 | Pin 10 | Pin 14 | Pin 15 |
|---|---|---|---|---|---|---|
| J1850 PWM | Must have | – | – | Must have | – | – |
| J1850 VPW | Must have | – | – | – | – | – |
| ISO9141/14230 | – | – | Must have | – | – | Optional |
| ISO15765 (CAN) | – | Must have | – | – | Must have | – |
It’s important to remember that while these pinouts can be indicative, other pins might also be populated. These additional pins often connect to other vehicle systems beyond the engine control unit (ECU). Standard OBD2 tools are generally limited to communicating with the engine ECU. For diagnosing other systems like ABS, airbags, or body control modules, vendor-specific diagnostic software is typically required, such as FiCOM for Fiat/Alfa/Lancia, FoCOM for Ford/Mazda, or HiCOM for Hyundai/Kia.
Non-OBD2 Protocols
Beyond the standardized OBD2 protocols, vehicles also utilize a range of vendor-specific diagnostic protocols for in-depth diagnostics. These can include protocols like KWP2000 (in different implementations), KW1281, VWTP, KW72, and KW82. These protocols are used for more specialized or “native” diagnostics beyond the scope of generic OBD2 functions.
Understanding the OBD2 protocol list and how to identify them is a foundational step in vehicle diagnostics and repair. By knowing which protocol a vehicle uses, technicians and enthusiasts can select the correct tools and procedures for effective vehicle communication and troubleshooting.
