1998 Johnson Evinrude "EC" 150, 175 FFI Service Manual, P/N 520211, Page 54Get this manual
Warning System
FFI engines have protective feature that prevents powerhead damage due to an engine cooling system overheat, loss of oil flow, alternator output exceeding 26 volts, or excessive ECU temperatureThis feature is called S.L.OW(Speed Limiting Operational Warning)A number of devices monitor engine operating conditionsAll are linked directly to the ECU, which in turn is connected to the dash-mounted System Check gauge and hornA complete listing of failure modes and their effect on engine operation can be found under the Service Codes heading in the Diagnostics sectionInitiation
When the appropriate sensor or switch is activated, the ECU responds by interrupting fuel injector operationIt begins gradual five second drop in engine RPM to threshold limit of approximately 1800 RPMThis is accomplished by cutting out one cylinder at time, until total of five are affectedThe ECU simultaneously sounds dash-mounted warning horn and turns on the appropriate System Check gauge lightAs long as S.L.OWis activated, the engine will run normally below 1800 RPMAbove 1800 RPM, the engine will run poorlyRecovery