Fault Codes/Rehlko/ENGINE SPEED LOW SD *RehlkoENGINE SPEED LOW SD *UnclassifiedSpeedWhat This Code MeansEngine speed drops below 85% of the normal running speed for more than 3 secondsPossible Causes•Excessive generator load•Tripped enclosure thermostatSuggested Actions1Reduce the load2Check enclosure thermostat and reset if tripped3Contact an authorized dealer for serviceRelated Rehlko Fault CodesOVERCRANKSPD SENS FLT SDENGINE SPEED HIGH SD *ENG SPEED LOWENG SPEED HIGHADVANCED DIAGNOSTIC ACTIVEADVANCED DIAGNOSTICERRATICSIGESEXER NOT SCHBrowse all Rehlko fault codes→ASK RUDY ABOUT THIS FAULTGet a diagnosis walkthrough for ENGINE SPEED LOW SD * on your specific Rehlko unit — cited to the OEM manual, not a forum guess.TRY IT FREE