PANEL AS 3631597 - Caterpillar

System Operation
Although the rack solenoid (BTM) is capable of shutting the engine down, the shutoff solenoid provides a secondary means for the ECM to shut down the engine. When the solenoid receives a voltage, the solenoids' plunger is pulled in to allow the engine to run. When the solenoid loses the voltage, the plunger releases and the engine shuts down.If an overspeed condition is detected by the overspeed switch, the relay in the overspeed switch box will open causing the shutoff solenoid to release and the engine to shut down.With the engine running, the voltage at the shutdown solenoid connector should be between 1.5 and 2.5 VDC (from pin A to pin B).Schematic
For a more detailed schematic, refer to 3408/3412 High Performance Marine Engine Schematic, Form No. SENR5518.Diagnostic Codes
Functional Test