Which component is considered an actuator in engine systems?

• A. Oxygen Sensor
• B. Spark Plug
• C. Fuel Injector
• D. Alternator

Answer: (C)

An actuator is a device that converts an electrical signal into a physical action within the engine. The fuel injector fits this role because the engine control unit sends a precise electrical signal to the injector’s solenoid, which moves a valve to open and spray fuel at the right moment. That direct conversion from electrical control to a mechanical action that influences the air–fuel mixture is what defines an actuator.

The oxygen sensor is a sensor that measures exhaust gases to inform the ECU, not to create a physical action. The spark plug creates a spark by converting electrical energy into a spark discharge, but it’s part of the ignition system rather than a controllable actuator that regulates engine processes. The alternator generates electrical power, not a mechanical action within the engine.