This part is a kind of semiconductor called TMS374.

Function of this product has ECU DECODER.

Manufacturers : ETC

Image and pinout :

Some of the text within the PDF file :

TMS374 ECU DECODER Connection diagram: + :12v DC - : GND S :signal wire Introduction This Tool is a frequency sweeper with 5V square wave output (Duty cycle 50%, effective frequency range from over 10kHz (max 50kHz) to 50Hz) .This tool can be also considered as a MCU version of the software TMS-374 Decoder ECU. The only difference between the two tools is that the MCU version works without a PC. A small MCU is used to generate the pulses instead of the PC RS232 Tx line. Manual After powering the device on - the LED should blink twice. The sweeping process starts as power is supplied to the device. LED ON - means there are pulses on the output. After reaching the lowest frequency the LED goes off and the mcu stops the generation.      Connect the GND line to any suitable G [ ... ]

TMS374 PDF Datasheet Download