DTC P0778: 2-4 Brake Solenoid Valve Circuit Fault (Open/Short): Description
WARNING: This page is about a different car, the 2002 Mazda MPV. However, it is still accessible from the selected car via links, so may be relevant.
Open or short in 2-4 brake solenoid signal system (while TCM monitors solenoid output voltage, the voltage that differs from the ON/OFF signal output by CPU in TCM is detected).