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OBD-II Protocols

An OBD2 compliant vehicle can use any of the five communication protocols: SAE J1850 PWM, SAE J1850 VPW, ISO9141-2, ISO14230-4 (KWP2000), and since 2003 also ISO 15765-4/SAE J2480. ELM-USB and OBDTester support all of them.

Some websites say they support 9 or even more protocols. This is because they mistakenly count protocol variants as separate communication protocols. If you add 4 variants of CAN-BUS to our list, you are on 9.

Please note that some models are equipped with SAE J1962 connector, but these cars are NOT OBD2 compliant. Typical examples of such cars are some early VW/Skoda/Seat models (European versions only), Ford cars with EEC-IV using Ford DCL protocol (e.g. Ford Escort), Nissan EU/Asian models (using Nissan DDL protocol), or some European Hyundai models.

ISO15765-4 (CAN-BUS)

The most modern protocol, mandatory for all 2008+ vehicles sold in the US. Uses pins 6 and 14, communication is differential.

Four variants of ISO15765 exist. They differ only in identifier length and bus speed:

ISO14230-4 (KWP2000)

Very common protocol for 2003+ vehicles using ISO9141 K-Line. Uses pin 7.

Two variants of ISO14230-4 exist. They differ only in method of communication initialization. All use 10400 bits per second.

ISO9141-2

Older protocol used mostly on European vehicles between 2000 and 2004. Uses pins 7 and optinally 15.

SAE J1850 VPW

Diagnostic bus used mostly on GM vehicles. Uses pin 1, communication speed is 10.4 kB/sec.

SAE J1850 PWM

Diagnostic bus/protocol used mostly on Ford. Uses pins 1 and 2, communication signal is differential and it's rate is 41.6kB/sec.

Determining protocol from OBD-2 pinout

As a general rule, you can determine which protocol your vehicle is using by looking at the pinout of the OBD-II connector:
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 -
Please note that other pins may also be fitted. They usually connecto to other (non-engine) ECUs or provide various signals. Generic OBD2 tools are not capable of "talking" to other ECUs than engine. For diagnosis of other control units such as ABS, airbag, audio or body modules you need vendor-specific software such as FiCOM (Fiat/Alfa/Lancia), FoCOM (Ford/Mazda) or HiCOM (Hyundai/Kia).

Other non-OBD2 protocols

Almost every car uses also vendor-specific diagnostic protocols such as KWP2000, KW1281, VWTP, KW72, KW82, which are used for "native" diagnostics.
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