The DEBUGGER expansion is used to easily probe every output of the expansion pin socket, as well as to easily connect a JTAG debugger to the ECU.
A standard 20-pin JTAG connector is present on the debugger expansion. This allows the user to connect a debugger such as the ST-LINK V2 to easily develop and debug new firmware for the ECU.
Schematic of the JTAG circuitry
Pinout of the DEBUGGER expansion's connector