What is a Car Solenoid?

Dustin Hawley | Feb 26, 2021

If you really think about it, starting our cars as easily as we do every day is something of a modern miracle. We jump into our vehicles, turn a key (or even just push a button on many occasions), and then our engine instantly roars to life, harnessing the incredible power of an internal combustion reaction.

function of car solenoid in starting car

It’s certainly much easier and more convenient than if we had to start the engine in another way. There was a time when drivers had to start their cars by turning a crank. We sure have come a long way, but this convenient starting process is only made possible by your car’s solenoid. 

Not sure what a car solenoid is or how it works? Our guide will answer it all, so let’s get started.

Overview of a Solenoid

In a nutshell, a solenoid is one of the few components responsible for starting your car. It’s generally positioned between your vehicle’s ignition module and the engine.

Solenoids (also typically called starter solenoids or starter relays) operate by receiving both large electrical currents from your vehicle’s battery and smaller electrical currents from the ignition system when the car key is turned.

As the key is turned, the starter solenoid then closes two contacts or metal points together. In doing so, the solenoid relays electrical currents from the ignition to the starter motor. That begins a chain electrical reaction to start the combustion engine overall.

Think of the solenoid as the initial spark that starts your car’s engine and leads to all of its complex mechanical parts turning in unison. 

Where are Solenoids Located?

The location of a solenoid can vary depending on your vehicle’s make and model. Most cars have their solenoids mounted right on the starter motors, connected to other “starter” components like the starter gear and starter control terminal.

So what exactly is a starter motor, you ask? It’s essentially a magnetic and electric motor connected to your car’s battery, designed to receive low current power and begin turning the aptly-named starter gear, again turning to start a larger electrical reaction and (eventually) your entire engine.

However, a few cars have their solenoids mounted elsewhere in the engine compartment. Regardless, the solenoid is always located between the ignition and the engine, so check your owner’s manual to learn more about your solenoid’s exact location with your make and model.

Why are Solenoids Important?

Solenoids are critical car components since they allow your ignition system to reach the starter motor and, in turn, cause your car to turn on in the first place.

Without a solenoid, turning your key wouldn’t start your car at all. However, you could still start your vehicle by directly interacting with the battery and starter motor. But starting your car this way would require you to pop the hood of your vehicle before each drive. That procedure might even be impossible, depending on the complexities of your car’s engine bay.

Therefore, it’s essential to make sure that your solenoid is working correctly at all times. It’s a vital component if you want to enjoy the convenience of key-turning engine ignition.

How Does a Solenoid Work?

Let’s break down the solenoid engine starting process in a bit more detail:

When you insert your key into the ignition and turn it, the action sparks a small electrical current that is sent from the ignition switch to the starter solenoid. When the solenoid receives this current, it closes a pair of heavy metallic contacts. The contacts relay a proportionately larger electrical current through themselves and to the starter motor. The starter motor receives the current and begins to set the engine in motion.

What happens next? The engaged solenoid operates a lever called a plunger, which forces a component called a pinion into a meshed position with another part called a ring gear, locking them together. The ring gear is crucial since it clutches the engine and prevents the starter motor from spinning up to dangerous speeds.

It all sounds very technical, but this is the bottom line - your key turns in the ignition and sends electricity through the starter solenoid, which sends the electricity to the starter motor, which starts the rest of your engine and allows it to run smoothly.

How Solenoids Can Fail

Solenoids are extremely critical parts for proper automotive function, and while they are modestly durable, solenoids can still fail under certain circumstances. A malfunctioning solenoid will prevent your engine from starting when you turn the key in the ignition.

It’s important to know how solenoids can fail so you can identify potential malfunctions and repair your vehicle or bring it to a mechanic as soon as possible. In most cases, solenoids stop working when they don’t receive enough power from the battery.

In this case, the solenoid won’t provide the necessary electrical current to the starter motor. A low power malfunction is characterized by a rapid clicking sound when you turn your ignition key. This loss of power can be caused by things like:

  • Low battery power overall
  • Corroded or weak connections in the battery cable
  • Damaged red cables connected to the battery housing


Your car’s solenoid is a small but vital component. It’s somewhat difficult to understate how helpful this little piece is, but without it, we simply wouldn't be able to hop in our cars, turn a key, and hit the road with the same ease that we do today.

Therefore, be sure to monitor your solenoid and pay attention to the potential symptoms of failure outlined above. These details should help you get your solenoid or battery repaired, recharged, or replaced if your car ever fails to start.

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