assuming you have used clear fuel lines to see if there is any air bubbles, the other most common cause of that fault code is a blockage. ie dirty fuel filter, something in tank or lines blocking the pickup, dented fuel line.
also check for air bubbles coming out of the injection pump.
one place often missed is the spill line. the injector connections sometimes leak and the injection pump sucks air in. as the connection is at the pump banjo clear fuel line on the pickup side doesn't show any bubbles.