The On-Board Diagnostics II (OBD-II) connector is a standardized diagnostic interface found in most modern vehicles. It allows mechanics and technicians to access information and perform diagnostics on various systems within the vehicle, such as the engine, transmission, and emissions controls. However, this connector can also be exploited by unauthorized devices or individuals to gain access to the vehicle's systems for malicious purposes, such as stealing the vehicle or tampering with its security features.

A device that blocks communication from the OBD-II connector to the vehicle's modules serves as a security measure to prevent unauthorized access and potential exploitation of the vehicle's systems. Here's a detailed explanation of how such a device works and its implications:

 Purpose: The main purpose of this device is to improve vehicle security by preventing unauthorized access through the OBD-II connector.

 Functionality: The device is installed between the OBD-II connector and the car's ECM.

 Blocking Unauthorized Access: Unauthorized devices, such as diagnostic tools or hacking devices, attempt to communicate with the vehicle's ECM through the OBD-II connector to gain access to sensitive information or control functions.

 Preventing Key Teaching: One specific example of unauthorized access that a blocking device can prevent is unauthorized key learning.

 Owner Control: By blocking unauthorized access through the OBD-II connector, the device gives the car owner control over who can access their car's systems.