The ELM327 Bluetooth diagnostic interface connects to the diagnostic socket of your vehicle. It allows you to diagnose the engine and transmission of your vehicle. Displays and clears fault codes The ELM327 Diagnostic Interface communicates with the engine and transmission systems of your vehicle to access diagnostic data. You can display fault codes, which consist of several characters, such as P0070. You have a fault code database on most software to find out what the fault code is and correct the problem (example: code P0070 = Outside temperature sensor - circuit failure / P0093 = Leak in the fuel system - significant leak detected.