Most people have never heard of a solenoid, and when their vehicles start having electrical problems, they automatically assume that the battery or the starter is dead.
Very possibly, it could have been the solenoid.
What Is a Solenoid?
A solenoid is just a coil of wire that's wrapped around a hollow, non-magnetic core. It receives an electric current from both the ignition switch as well as the battery.
The small electric current from the ignition switch forces the solenoid to clamp together a pair of heavy contacts. This allows the large electric current from the battery to flow to the starter and turn over the engine.
Generally, when a solenoid is broken, the two metal clamps won't operate anymore to complete the circuit, making it impossible for power to flow from the battery.
Diagnosing a Problem With Your Solenoid
If your car won't start and you've changed your battery or jumped it, and if there's no sound at all out of the starter when you turn the key, then it's a good bet that your solenoid is bad.
Depending on the solenoid, you may or may not be able to test it. Its job is simple: It connects the circuit between the battery and the starter. So when it's broken, it no longer is able to connect the battery to the starter. So testing is just a matter of bridging the connection and allowing power to flow from the battery to the starter.
If you have a metal tool with a rubber handle, you can touch both of the posts with the metal, thus bridging the connection and allowing power to flow. Just be sure not to shock yourself. This will not work in every case, however, because solenoids are different and not all of them have easily accessed ports like this.
We once had a riding lawnmower with a bad solenoid and would keep a long screwdriver in the glove box to use every time we needed to start it. We would reach in and touch the screwdriver to both the ports on the solenoid, and without fail, the lawnmower would start right up every time.
We eventually changed it out, but since the solenoid is a very simple part that only functions to bridge the connection between the battery and the starter, we figured it wasn't that big of a deal. In fact, having an easily accessible faulty solenoid is actually quite a good anti-theft system.
How Do Solenoids Break?
Your car's solenoid can break for a variety of reasons. One is just normal wear-and-tear, which causes all automotive components to eventually wear out. Another factor that can cause it to go bad is poor technique in jumpstarting a car. If you've jumpstarted your car recently or helped a friend jumpstart theirs, then it's possible that you've accidentally knocked out your solenoid.
When the jumper cables are hooked up to your battery posts, if you accidentally touch the copper of the other two jumper cables together, it'll send a spike of power through your system that can knock out your solenoid.
This generally happens to the car that's doing the jumpstarting and not the one with the dead battery. Generally, poor jumpstarting technique happens when a person hooks up the cables to the powered battery first, and then while walking over to hook up the dead car, the heads of the other two cables touch, thus sending a surge through the system which either knocks out the solenoid, or else weakens it so that it becomes faulty and fails at a later date.
So don't ever touch the heads of the jumper cables together.
How Do You Replace a Faulty Solenoid?
If you've got a faulty solenoid and you want to replace it, it should be a fairly simple process, depending on whether or not it's buried under other components.
If your electrical system is constantly acting up and you've already replaced the battery and don't know what to do, it might be a good idea to slowly start replacing the rest of the starter system.
The solenoid is a good place to start because it's a small part with little installation. If you go into your local auto parts store and find the solenoid you need for your car, they should be able to give you further instructions on how to install it.
Just make sure you disconnect your battery first so that you don't accidentally shock yourself.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
© 2011 Benji Mester