There are two different Subaru Impreza WRX V10 ECUs available. These are categorised as 2004-2006 2500cc and 2007 2500cc. This maybe slightly misleading as some 2006 vehicles require a 2007 ECU.
It is critical that the correct ECU for the vehicle is installed, failure to install the correct ECU can result in engine component, engine wiring or ECU damage.
The correct ECU can be verified by studying the wiring loom.
If pins A1, A2 and A3 (see pinout section) contain no wires, then the correct ECU required is the 2007 2500cc version. If these pins contain wires, then the correct ECU is the 2004-2006 2500cc version.