Three Signs That Your Main Relay Is Not Working (& How to Replace It)

The modern automobile is an electrical wonder. And while this electrical ingenuity has led to a wide array of features that wouldn’t otherwise be possible, they can start to act up and create a bit of a headache.

The main relay is a key component in these electric marvels. These relays should not fail and will last the entire life of your vehicle. However, sometimes a relay can break. The good news is that if you suspect a bad main relay, it’s pretty easy to rule out, and it’s cheap to replace.

Below we’ve highlighted the most common signs of a bad main relay before diving into what it does and where you can find it. Let’s begin with the signs to look for.

Bad main relay symptoms

The most common symptom of a bad main relay is that you won’t be able to start your car, and nothing happens when you turn the key. You may also notice warning lights or engine stalling in your car.

Below we’ve highlighted a more detailed list of the three most common causes of a bad main relay.

1. Unable To Start Your Vehicle

If you try to start your vehicle and it won’t start, there’s a chance that you have a bad main relay. It is important to rule out any other problems, such as a dead starter or a low battery before rushing to replace the bad main relay.

If you’ve verified that your battery has enough power, you can turn the key to different ignition spots and listen for a click from the fuse box. If you hear a click, then your main relay isn’t the problem – if you don’t, you’ll need to investigate further. Keep in mind that you vehicle must have enough power from its battery to cause the relay to click.

2. Make sure your engine light is on

If you can start your vehicle, you’ll notice a check engine light on the dashboard if you have a bad main relay. To verify that the engine light is for the main relay, you’ll need to connect an OBD II scan tool and read what the code is for, though.

3. Your Vehicle Won’t Stay Running

If you can start your vehicle, if you have a bad main relay, you won’t be able to keep it running for long. Whether this is a matter of seconds or minutes depends on the specific fault, but you’re not going to keep your engine running with a bad main relay.

If your engine is running and stays that way, whatever problem you’re experiencing isn’t related to the main relay.

Main Relay Function

Your vehicle’s main relay gives power to your car’s most electric components, like the engine control unit and other control modules. It shifts to a new position every time you turn the vehicle on. This gives you the ability to get power to any necessary parts of your vehicle when it is turned off.

Relay Point Main

Your vehicle’s main relay is typically in your vehicle’s fuse box. This fuse box can be found in two places. The first is under the dashboard. You can have it in the engine compartment.

Either way, it should have a fuse box cover that you’ll need to access the main relay. From there, you’ll need to determine which relay is the main relay in the fuse box. You might find every relay and fuse labeled inside the fuse box. Others will need you to search a bit more.

You’ll need to scour the web or your owner’s manual for a fuse box diagram if it’s not on the inside of the fuse box cover.

Replacing the main relay cost

Depending on the type of vehicle and location, you will pay between $70 to $120 for a main relay replacement. Most of this cost comes from the troubleshooting fee and cost of the relay.

That’s because while diagnosing your main relay can be a bit complicated if you don’t know what you’re doing, replacing it is easy. The relay itself costs anywhere from $30 to $70, while labor usually runs another $40 to $50.

If you are certain that the relay is the issue, remove the cover from the fuse box to replace it. If you are certain that the relay is the issue, swap it out with the other relay. If the problem “moves” you have a defective relay, and you need to replace it.

Diagnostics of your Main Relay

While a faulty main relay is rare, it’s not impossible or unheard of. Although diagnosing a main relay problem requires some technical knowledge, you have a few options.

The first step is to find the main relay. As you turn the ignition, make sure someone is standing near the fuse box. They should hear a clicking noise, if they don’t, then you might have a faulty main relay. If they do, chances are the relay isn’t the problem.

It doesn't matter what, you could swap one relay with another if it can be identified. Although they may technically be both defective, there are very few chances that this will happen. Once you’ve swapped the relays, try starting your vehicle.

You need to replace the relay if the vehicle does not start but it is acting up in the system that you had to move the main relay. However, if you don’t notice any difference and the vehicle still won’t start or stay running, chances are the main relay isn’t the problem.

Keep in mind that you can have an electrical problem in your main relay circuit – which means that the main relay will look like the problem but replacing it won’t ever help. If this is the case, you’re going to need a little technical know-how to track down what’s going on.

FAQs about Main Relay