Are you sure that is what the code means? And the impeller has nothing to do with coolant...BUT it does have something to do with cooling water flow. I know computerized newer generators have a flow sensor. If it is indeed a raw water flow issue, then you have changed the impeller. I would have checked the strainer first...then I would have checked to see if I had flow coming out of the thru hull by pulling the hose and checking.
BUT...if it is indeed a coolant issue...and you have coolant...then like someone said, check to see if it is a bad sensor.
Prairie 29...Perkins 4236...Sold
Mainship Pilot 30...Yanmar 4LHA-STP...Sold
Carver 356...T-Cummins 330B...Sold
Meridian 411...T-Cummins 450C