The automatic transmission is based on different levels of hydraulic pressure to give the torque converter and shift interlock actuator. This pressure is controlled by at least one solenoid. This entire system is controlled by the PCM (Powertrain Control Module).
When the problem code P0776 OBDII is stored, it is because the PCM found a problem with the transmission pressure control solenoid B. The solenoid is not working properly or is stuck in the off position.