Solenoids are used in many locations throughout a vehicle. They can start a reaction that ends in an action such as closing a valve, generating a spark, etc. Solenoids are a helix coil of metal wire. The center of the coil is iron and moveable. When an electric current is passed through the solenoid, a magnetic field is generated. Many solenoids are in use in tandem with a magnet which can affect vacuum creation, valve opening or closing, etc. Many other solenoids are used on their own as electromagnets to affect an action. The solenoid creates magnetic fields that are very small, often within an enclosed space. This technology is used all over a vehicle. Many valves operate by solenoid. Switches and relays are also often operated by solenoid. Some of the systems that solenoids operate in are brakes, clutch, exhaust gas recirculation, combustion, air intake, ignition, etc.