37840-R70-A01 Tdc Sensor Assembly - Overview. The 37840-R70-A01 Tdc Sensor Assembly is a crucial component for Honda marine engine systems. This sensor supports the ignition system by accurately detecting the top dead center (TDC) position of the engine's crankshaft, enabling precise ignition timing. By ensuring efficient engine operation, it plays a vital role in maintaining the reliability and performance of Honda marine engines. Engineered to factory specifications, it ensures seamless integr