Automatic transmissions rely on varying degrees of hydraulic pressure to shift gears and engage transmission components such as clutches and belts. To make these shifts efficient, the vehicle’s computer uses pressure control solenoids to direct transmission fluid from one hydraulic circuit to another.
For automatic transmissions to achieve an efficient process for setting gear ratios, the fluid must be channeled precisely. If a pressure control solenoid fails, the fluid cannot be effectively controlled. If the Powertrain Control Module (PCM) detects that the output voltage of the pressure control solenoid “B” is problematic or out of range, it will set DTC P0778 OBDII.