ETR Solenoid (Energize To Run)
An ETR type fuel solenoid is the type that must be continuously energised for the engine to run: the moment power is lost, fuel is cut and the engine stops. Because the engine stops by itself when the ignition switch is turned off or when a wire breaks, it is a solution that naturally stays on the safe side.
ETR solenoids usually have two windings: a strong pull-in winding energised briefly during cranking to pull the lever, and a low-current hold winding that maintains the position. This is why a short high current pulse is seen on some engines when the ignition is switched on.
- Safety advantage: loss of supply directly means shutdown. The emergency stop button is wired so that it breaks this line.
- Disadvantage: when the battery weakens or a terminal loosens, the engine can stop unexpectedly.
- Engine protection switches — low oil pressure, high coolant temperature — provide shutdown by breaking this line.
When installing an electronic throttle kit, the ETR line is not touched. The supply of the GS740 and GS740-3P and the supply of the solenoid must be considered separately; cutting the kit's supply does not stop the engine, it only lets the throttle lever fall to idle.
Context in which this term is used: Electronic speed and throttle control on a diesel engine