Probable Causes

WARNING: This page is about a different car, the 2014 Mitsubishi Outlander. However, it is still accessible from the selected car via links, so may be relevant.

Malfunction of CAN bus system.
Damaged harness or connector.
Malfunction of the fuse No.14.
Malfunction of the stoplight switch.
Malfunction of the ETACS-ECU.
Malfunction of the ECM.