The option DIAG is used to read/write the ECU via diagnostics through the OBDII port of the car. It allows you to read and write the ECM Maps, Internal/External Flash, Data flash.

It allows you also to perform both real and virtual read of the memory.

Select Diag and the car brand you want to work on

Select the ECU brand you want to work on

Select the memory type you want to read/write followed by Info, Read or Write.