J2534 is an interface standard developed by the SAE (Society of Automotive Engineers) and mandated by the US EPA (Environmental Protection Agency) for the reprogramming of vehicle ECUs. Its purpose is to create an API (Application Programming Interface) that is adopted by all vehicle manufacturers to allow independent workshops to reprogram ECUs without the need for special tools accessible only to authorised dealers. In short: en .

SAE J2534 consists of two parts: -1 and -2. SAE J2534-1 defines functions for a device that performs reprogramming of emission control devices (and could also apply to non-emission control devices).

SAE J2534-2 defines optional functions for a device that performs reprogramming of other non-emission ECUs. It also provides a way for a vehicle manufacturer to reprogram all ECUs in their vehicles “using J2534” by publishing necessary protocol information about non-emission-related ECUs.

The US EPA regulation requires all automobile manufacturers to implement J2534 pass-through reprogramming for their emission control devices beginning with the 2004 model year. If a manufacturer cannot be J2534 compliant by model year 2004, they can apply for a one-year extension. In addition, the specification includes a provision that allows manufacturers to use the J2534 reprogramming method for model year 1996 through 2003 vehicles as long as they provide any necessary additional hardware (e.g., vehicle connector cables for use with the unit and/or additional connectors) for the aftermarket. If a manufacturer cannot retrofit the J2534 pass-through reprogramming solution, with or without special cables, they must provide equipment and tooling companies with all the information needed to develop aftermarket equivalents of their manufacturer-specific reprogramming hardware and software.

J2534 pass-through reprogramming is only required for emissions-based ECUs (e.g. powertrain, engine, transmission, accelerator pedal control) and is mandatory for all vehicles beginning with the 2004 model year. Additional support for reprogramming of chassis and body ECUs depends on the individual capabilities of each manufacturer's reprogramming application software.