As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CRUISE, ''RUDDER RATIO, L-HYD SYS PRESS'' MESSAGE SHOWN ON EICAS AND L-DEMAND PUMP LOW PRESSURE LIGHT ON. AIRCRAFT AIR TURN-BACK AT CKS APIRPORT. GROUND CHECK FOUND L-HYD SYSTEM PRESSURE SWITCH FAILED. REPLACED L-HYD SYSTEM PRESSURE SWITCH AND GROUND OPER CHK CONDITION IS NORMAL. (X)