How to Tell if a Relay is Bad in a Car, Truck, or SUV

1. Signs of a failing or bad starter relay in a car

Below are the common signs indicating your car has a bad starter problem;

1.1. Car won’t start

This is still the most obvious warning symptom of a problematic starter relay in a vehicle. Whenever you turn the key of your vehicle or press the ignition button and the vehicle refuses to start as you keep trying, suspect your ignition’s starter relay.

A bad starter relay in a car usually make a driver

A bad starter relay in a car usually make a driver face problem with the vehicle’s overall ignition system

1.2. Starter remains on after engine’s already started

Normally, after you have successfully started the engine in your car and stopped pressing the “start” button or released the keys, power should be disconnected from the vehicle’s starter motor. But in any case, if in your car, the starter still stays on after the engine has been started, then there must be a problem with the starter relay of such a car.

>>> Some problems are clearly informed on your car dashboard. Check them here! Battery warning light: Five factors that might be responsible

1.3. Intermittent problems with starting up the car

The starter relay of an ignition system of a car usually suffers from debris, dirt, and excessive heat that eventually causes a problem of sporadic operations of a vehicle’s starter.

1.4. Starter making some “Clicking” sound

This sign is commonly observed when a car battery is getting low on charge, but it is also a clear indicator of a failing starter relay which is suspiciously not delivering the full signal in the setup. 

When your car won’t crank or start part 3: How to check relays, fuses, switches and wires


How Much Does It Cost To Test a Relay?

It doesn’t cost hardly anything to test it as many mechanics will test a relay for free. Replacing one is pretty cheap as some can cost as little as $5. However, some can cost up to $100 and you will still need to pay for labor to replace it. That is inexpensive as well with the average cost between $35 to $75. 

Are Relays Interchangeable If A Relay Is Bad?

There are various types of relays available, each with its own specifications and power ratings. If the power rating is too different, the voltage may either be too high or too low.

What causes a relay to fail?

Several factors can cause your car relay to fail, and they include;

Corrosion: Corroded leads or connectors cannot transfer the required amount of current. It will result in starting issues. It can be intermittent starting, a clicking noise from the relay, or an idle vehicle that cannot start.

Dirt and debris: This component is usually protected from dirt, debris, and grimes by placing them under the dashboard or hood. Over time, debris and dirt will accumulate and affect the functionality of the relay. As the dirt clump, it’ll not allow adequate flow of current, and you’ll hear a series of buzzing or clicking sounds from the relay.

Bad connectors: A defective or broken connector is a significant cause of a failed relay. The relay will not function properly if the required amount of current is not passing through. It will display some signs by giving a series of weak clicking sounds and unable to carry the starting circuits. Aside from the series of weak clicks, the vehicle may refuse to start.

Too much heat: If high voltage passes through the relay continually, it will generate excess heat that will burn or melt contacts causing them to stick together. This will close the starter circuit even when the ignition is off. This effect requires immediate attention because it can lead to damaging the entire starting system.

Overly aged relay: starter relay issues may not have any significant cause. It might be an overly-aged relay that has last hundreds of miles. An old relay may have a deteriorating part that can’t function properly. If this is the case, you need to replace the relay, Nothing more.

Now that you have known the symptoms and causes of a bad starter relay, how do you fix it? The answer depends on the cause of the failure. If it is caused by dirt or debris, cleaning them will be the best option. And if it is caused by excess heat or bad connectors, consider replacing them. That takes us to how to fix faulty starter relay problems.

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5. Symptoms of starter relay failure

The starter relay, like other mechanical and electronic components in your car, will show signs of failure before it finally stops. Some signs of damaged or worn starter relays are listed below. If you see these warning signs, please make an appointment with a local ase-certified mechanic to conduct a thorough inspection of your car, as these symptoms may indicate a problem with other components.

When we turn off the ignition switch, both the starting solenoid and the motor should stop working. When the starter relay doesn’t operate in this order, the engine won’t start. It is likely that the main contacts are already welded together, in the closed position. If this happens, the starter relay will be trapped in the start position, causing damage to the starter, circuit, relay and drive flywheel, if not dealt with immediately.

1) The vehicle cannot be started

1) The vehicle cannot be started

The failure of a car to start is one of the most obvious signs of a car breakdown. Although many potential failures may prevent the car from starting, the failure of the starting relay is often the source of the problem. To understand why, we must first understand the function of the starter relay better.

When you turn the ignition key, your battery is shaken, releasing a burst of electrical energy. The starter motor is triggered by this energy and turns your engine. A starting relay completes the circuit before reaching the starter motor, but also increases battery current when it passes through it.

A defective starter relay will prevent your battery from delivering electrical signal to your starter motor. Therefore, no matter how many times you turn the key, your engine will not start. When you turn the key, if the circuit is not broken, you may hear a click. In either case, you should get professional help to evaluate the symptoms and accurately diagnose the cause.

2)The start relay remains open after the engine is started

The starting relay and the starting solenoid send current to the ignition switch when you turn on your ignition.The starter motor rotates the flexible board to start the engine, and the solenoid supplies power to the flexible board.

When we turn off the ignition switch, both the starting solenoid and the motor should stop working. The main contacts of the starter relay are probably already welded together, in the closed position, if it does not operate in this order, the relay keeps the engine started. If this happens, the starter relay will be trapped in the start position, causing damage to the starter, circuit, relay and drive flywheel, if not dealt with immediately.

It usually happens when the relay touches anything or is exposed to a lot of electricity. Because this problem may damage the entire boot system, it must be diagnosed and dealt with immediately.

3) The starter makes a clicking sound

Relays usually operate on an all-or-nothing basis. It either sends the entire current, or it sends nothing. However, when the starter relay is destroyed, only a part of the signal can be sent.

The starter relay makes a clicking sound, but the engine does not rotate, which indicates that the starter motor is not receiving enough current from the relay. This may also be a sign of low or exhausted battery power. Only when it transmits enough current to the starter, the relay starts to work. Smaller power may damage the entire starting device or cause the vehicle to fail to start, accompanied by annoying clicking sound.

Both of these conditions may be caused by corroded or aging relays with damaged contacts. Cleaning the contact points to ensure the correct flow or replacing the old relay are the only two options for repair. Scrape the corroded surface of the relay with sandpaper or a gravel scraper. You can replace the relay to get a larger output, or you can contact a professional mechanic.

4)The vehicle starts intermittently

When the starter relay is working, it transmits power to the starter every time it is turned on. However, debris, dirt and high temperatures can contaminate this ingredient. Corrosion and residues in the circuit restrict the flow of current. Due to these conditions, the starting relay may be forced to work intermittently.

The starter relay is the basic component of the ignition system and has very few moving components, which is why it rarely fails. However, when it happens, it is due to conductivity issues. If the relay is not malfunctioning, there may be a damaged or corroded wire connection under the hood.

What does a relay do in a car?

Relays are switches controlled by electrical power, like another switch, computer or control module. The purpose of an automotive relay is to automate this power to switch electrical circuits on and off at particular times.

How do Relays Work?

A car relay works like a switch that’s controlled by electrical power. When you turn on something in your car that requires a lot of current, say your wipers, horn, or lights; the current is passed through the relay where two pints of contacts close to power the accessory. 

A typical car relay has two circuits – an energizing circuit that has a coil and a contact circuit that has a lever. To better understand how these work, we will take the example of a vehicle’s horn.

A car’s horn comes with a four-pin relay. Two of the pins sit opposite each other and are connected to the coil. The other two are connected to the horn with an open contact between them. Each pin will have its own number to make it easy to identify the power source. 

When you press the horn button on your steering wheel, current flows through the two pins that are connected to the coil. This coil then generates an electromagnetic field that attracts a lever found along the contact circuit. The lever closes the point of contact, allowing the current to reach and activate the horn. 

How to Test a Relay in Your Vehicle


When you suspect that something is going wrong with one of the relays in your vehicle you can take it to a mechanic to get it checked out or you can go through the process of getting the relay tested on your own. testing your own relays is not overly complicated and if you’re comfortable doing any work in your vehicle, you may be able to handle this job on your own.


Step 1: You should use a test light and check the fuses in your vehicle before you proceed with checking the relays just in case the problem is with a few rather than the relay burning it. Every electrical component will have a fuse in the system as well that you can check and replace if necessary. Automotive fuses are typically very cheap and should cost you under $10.


Step 2: If you check under the hood of your car you should have something called a power distribution centre or PDC.  This provides a map for relay locations and what each one does. This will be handy for you to find the exact relay you need to address whatever problem you are experiencing with your vehicle. If you don’t have a location map for all the relays in your vehicle on your PDC anywhere, you can check out your owner’s manual and it should provide the same information. If that fails, the internet will definitely have what you’re looking for so you can Google your make, model, and year and the relay you’re looking for and you should be able to find exactly where you need to go.


Step 3: Now that you’ve located the specific relay that you’re looking for, gently take hold of the relay that you’re looking for and have someone turn the vehicle on.  All you need to do is hold the relay between your fingers, there’s no need to pull on it or move it. As the engine cranks over, the relay should click in one of the ignition switch positions. If that happens, then you know this relay is working properly. If it doesn’t happen, then you need to proceed.


Step 4:  Turn off your car and now you can remove the relay to inspect it at this point. Get a firm grip on it and pull forward, give you a bit of a wiggle if you need to help it come out.


Step 5: Give the relay a quick visual inspection. The terminals on the underside should be clean. If you see any signs of corrosion or damage from heat, you’re going to want to replace the relay.


Step 6: You need to do an inspection of the terminal that the relay came out of. The terminals are encased in plastic, so if there’s been an issue with overheating you may see some melting or evidence of burning around them. That also indicates you need to replace the relay. If you’re seeing just a bit of mild corrosion, you could use an abrasive tool of some kind to scrape the corrosion clean and give it a good buff so that it is in proper working order again. 


Step 7:  The relay should show an illustration of the internal circuit that it applies to. On the primary side of a relay you’re going to find terminal 86 and 85.  Power from the switch comes into the relay at pin 85 and it heads out to the ground at pin 86. That makes the complete circuit activating the electromagnet. The magnet closes the second circuit in the relay that runs from pin 87 to pin 30.


High amperage current from the battery enters the relay at pin 87. Pin 30 is where the current flows to whatever component it controls. 


Step 8:  To check any relay to make sure it’s working properly the only tool you really need is a multimeter. Once you have the relay removed you can set the multimeter to measure DC voltage and check to see if there are 12 volts located at pin 85 in the fuse box where the relay plugs in. If there is no voltage there you need to check the appropriate fuse for whatever component that you are checking.  


Step 9: If you confirm that there’s voltage in the 85 position then you can turn your multimeter to continuity and check just make sure that you have a ground at the 86 slot. If that is in good working order, then you can move to the 87 and check for voltage there. If you have no voltage present at the 87 point, then you may also have a blown fuse or problem with the circuit breaker.


Step 10: Return the multimeter to the continuity function and you can check the 30 terminal by placing one lead there and the other on the component positive voltage connection point. If that looks alright, then the relay is very likely the problem so you can replace it.


Step 11: If you’re not sure that you performed all of the steps properly, it never hurts to do a double check just to make sure everything is working the way it is supposed to be. 



What happens when a relay breaks?

If the ignition relay shorts, burns out, or otherwise fails while the engine is operating it will cut off power to the fuel pump and ignition system. This will cause the vehicle to immediately stall due to fuel and spark being cut off.


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