Possible causes

– Low transmission fluid level
– Dirty transmission fluid
– Faulty line pressure solenoid ‘B’ valve
– Line pressure solenoid ‘B’ valve harness is open or shorted
– Line pressure solenoid ‘B’ valve circuit poor electrical connection

When is the code detected?

Engine Control Module (ECM) detectes an open or shorted condition on the solenoid circuit

Symptoms

– Engine Light ON (or Service Engine Soon Warning Light)
– Transmission shift shock

P0778 TOYOTA Description

The line pressure solenoid valve regulates the oil pump discharge pressure to suit the driving condition in response to a signal sent from the Transmission Control Module (TCM).