Fault Codes/Rehlko/516600 4Rehlko516600 4UnclassifiedGeneralWhat This Code MeansSCR system (Secondary 1 DCU Sensor supply) - Critical under-voltageRelated Rehlko Fault Codes516663 0516663 31516600 3516666 1516284 17516667 31516281 15A-22760063ACCY PWROVER WARNING62ADBrowse all Rehlko fault codes→ASK RUDY ABOUT THIS FAULTGet a diagnosis walkthrough for 516600 4 on your specific Rehlko unit — cited to the OEM manual, not a forum guess.TRY IT FREE