J2534 refers to a standard protocol that enables communication between a vehicle's on-board computer system (ECU) and a diagnostic tool or software application. It is also known as the J2534 API (Application Programming Interface) or the J2534 Pass-Thru standard.

The J2534 standard was developed by the Society of Automotive Engineers (SAE) to establish a common interface between vehicle manufacturers and aftermarket tools or software. It allows third-party diagnostic tools to communicate with a vehicle's ECU, providing access to various functions and data for diagnostics, programming, and reprogramming purposes.

By using the J2534 protocol, automotive technicians and service professionals can perform tasks such as reading and clearing diagnostic trouble codes (DTCs), viewing live data from the vehicle's sensors, performing system tests, and updating ECU firmware or software.

The J2534 standard defines the communication protocols, message formats, and procedures that must be followed to establish a successful connection between the diagnostic tool and the vehicle's ECU. It ensures compatibility and interoperability across different vehicle makes and models.

To utilize the J2534 standard, a compatible hardware interface device, known as a J2534 pass-thru device, is required. This device acts as a bridge between the diagnostic tool or software and the vehicle's ECU, facilitating the communication using the J2534 protocol.

Overall, the J2534 standard plays a crucial role in enabling effective diagnostics, programming, and reprogramming of vehicle ECUs by providing a standardized interface for aftermarket tools and software to communicate with the vehicle's on-board systems.