Automatic transmissions use fluid pressure to activate transmission shifts. This performs gear shifts, achieves Torque Converter Clutch (TCC) lock-up, and smoothes shift points for better drivability. To obtain line pressure for these functions, pressure control solenoids are used.
According to the manufacturer, the pressure control solenoid “B”, contributes to gear shift control and locks the TCC. It does this by regulating the fluid pressure of the belts and clutches. This solenoid is electronically controlled by the PCM (Powertrain Control Module) or TCM (Transmission Control Module).
When the P0777 OBDII fault code is displayed, it is because the pressure control solenoid “B” is stuck.