DTC B1500 Keyless UART Com. Malfunction: DTC Detecting Condition
WARNING: This page is about a different car, the 2008 Subaru Impreza. However, it is still accessible from the selected car via links, so may be relevant.
UART between keyless entry control module and body integrated unit is open or shorted, the connector is not connected properly, or the terminal is crimped improperly, keyless entry control module internal error.