Possible causes

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

Tech notes

There is a factory service bulletin for the 2004 Toyota Sienna
2004 Toyota Sienna Factory Service Bulletin OBDII Code P0748

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

P0748 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).

TOYOTA Technical Service Bulletins for P0748 code