Compatible with MEFI-1 thru MEFI-4 marine EFI systems, the CodeMate marine Engine Control Module (ECM) continually checks the integrity of its sensors and controls. When a problem is detected, a Diagnostic Trouble Code (DTC) is set and retained in the ECM's computer memory. These stored trouble codes are intended to assist a service technician in diagnosing engine and control system problems. The CodeMate Tester tool provides the technician with three separate diagnostic functions. It can be used as a system Malfunction Indicator Lamp (MIL); a trouble code display & erase tool; and a base spark timing tool. This tool is not for use with MEFI-5, MerCruiser PCM-555, ECM-555, Volvo Penta EGC or other marine EFI systems. - This part is non-refundable if opened