Inspection Procedure 15: The Trunk Is Not Opened When The Keyless Operation Key "TRUNK" Button Is Operated: Notes
WARNING: This page is about a different car, the 2012 Mitsubishi Lancer. However, it is still accessible from the selected car via links, so may be relevant.
CAUTION:
Before replacing the ECU, ensure that the power supply circuit, the ground circuit and the communication circuit are normal.