Subaru Impreza 2002 Service Manual page 3155

POWER ASSISTED SYSTEM (POWER STEERING)
Trouble
Vibration
While engine is running with/
without steering turned.
GENERAL DIAGNOSTIC TABLE
Possible cause
Too low engine speed at start
Vane pump aeration
Damaged valve in oil pump, gearbox
Looseness of play of steering, suspension parts
PS-112
Corrective action
Adjust and instruct customers.
Fix the wrong part.
Vent air.
Replace the oil pump, faulty parts
of gearbox.
Retighten.