What Is a Solenoid in a Car?by Tracy Underwood
According to Webster's New Collegiate Dictionary, a solenoid is "a tubular coil for the production of a magnetic field." This magnetic field is what moves a spring-loaded steel or iron plunger within the solenoid when an electrical current is present.
In automotive use, a solenoid is usually a heavy-duty electrical relay. The plunger opens or closes a set of electrical contacts when a small control current is present in the coil.
The most common use for a solenoid in a car is to control the starter motor. The starter must produce enough power to rapidly spin the engine until it starts, and this requires a large electrical current. Because a car's ignition switch is not large enough to carry enough current to operate the starter, the ignition switch controls the solenoid, which can produce the necessary current.
Fluid or Pneumatic Valve
Most cars have a variety of valves to control fluid or vacuum in the transmission, climate control, and emissions control systems. When such a valve uses an electrical impulse for activation, it is called a solenoid.