How Do 12V Car Solenoids Work?

Written by dan ferrell
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How Do 12V Car Solenoids Work?
(A solenoid's magnetic field (photo courtesy of Nmnogueira at

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The Solenoid as Actuator

Solenoids may act under your control as a driver or passenger, or the control of the vehicle's computer-Engine Control Unit (ECU). You may order a solenoid to lock or unlock the electric door locks by pushing a button, for example. In the same way, the computer may order solenoids to regulate temperature, vacuum flow, pressure and other tasks for best engine performance.

How a Solenoid Operates

Every time you push the button on your electric door lock, electrical energy travels to a solenoid. This electrical current then travels through a small winding in very close proximity to a metal core inside the solenoid. The magnetic filed created by the current on the winding causes the core to move and act on the lock mechanism to lock or unlock the door.

Different Types of Solenoids

Some electromechanical solenoids are equipped with a return spring. This helps the core or plunger inside the solenoid to return to its original position once electrical current is shut off. A starter solenoid functions this way. Other solenoids are equipped with a reversible motor. This helps the plunger inside the solenoid to execute an "order" in two different ways. Automotive electric door locks use this type of solenoid to lock and unlock doors. Still other solenoids may act in proportion to voltage signals for more precise control, like fluid pressure flow inside a transmission.

Different Uses

Uses for automotive solenoids may vary widely, depending on vehicle make and model. A solenoid may be part of a relatively simple electrical circuit to engage the starter motor, to trigger engine control devices or act as an interlock device to prevent the engine from starting without the proper ignition key or the transmission in gear other than Park or Neutral. On more sophisticated electrical circuits, a solenoid may act as vibration damper on engine mountings, while others may help regulate oil pressure inside an automatic transmission.

Precision Control

Proportional or limited movement solenoids are widely used in precision control circuits to operate pistons, valves and fluid flow inside a transmission or fuel injection system in modern vehicles. These solenoids have limited travel motors to provide accurate and smooth pressure control.

Electronic Control

The modern solenoid is also part of a complex and precise electronic automotive control system. Different integrated and interrelated automotive systems use solenoids to control shaft speeds, vacuum, spark advance, injector parameters, transmission shift changes, engine temperature and dozens of other events to allow for better emissions, acceleration and fluid control.

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