ELM327

The ELM327 is a programmed microcontroller produced by ELM Electronics for translating the on-board diagnostics (OBD) interface found in most modern cars. The ELM327 command protocol is one of the most popular PC-to-OBD interface standards and is also implemented by other vendors.

The original ELM327 is implemented on the PIC18F2480 microcontroller from Microchip Technology.

ELM327 is one of a family of OBD translators from ELM Electronics. Other variants implement only a subset of the OBD protocols.

The ELM327 abstracts the low-level protocol and presents a simple interface that can be called via a UART, typically by a hand-held diagnostic tool or a computer program connected by USB, RS-232, Bluetooth or Wi-Fi. New applications include smartphones.

There are a large number of programs available that connect to the ELM327.

The function of such software may include

The protocols supported by ELM327 are:

The ELM327 command set is similar to the Hayes AT commands.

The ELM327 is a PIC microcontroller that has been customized with ELM Electronics' proprietary code that implements the testing protocols. When ELM Electronics sold version 1.0 of its ELM327, it did not enable the copy protection feature of the PIC microcontroller. Consequently, anyone could buy a genuine ELM327, and read ELM's proprietary binary microcontroller code using a device programmer. With this microcode, pirates could trivially produce ELM327 clones by purchasing the same microcontroller chips directly from MicroChip and programming them with the copied microcode. ELM327 clones were widely sold in devices claiming to contain an ELM327 device, and problems have been reported with the clones. The problems reflect bugs that were present in ELM's version 1.0 microcode; those making the clones may continue to sell the old version.

Although these pirate clones may contain the ELM327 v1.0 code, they may falsely report the version number as the current version provided by the genuine ELM327, and in some cases report an as-yet non-existent version. Released software versions for the ELM327 are 1.0, 1.3a, 1.4b and 2.1 only. The actual function of these pirate clones is nonetheless limited to the function of the original ELM327 v1.0, with inherent deficiencies.

...
Wikipedia