Home Diagnosis and TroubleshootingElectrical System and Electronics How To Test A Relay – How Can You Do It With A Multimeter?

How To Test A Relay – How Can You Do It With A Multimeter?

by Jordan Harris
How To Test A Relay

How to test a relay? Every car on the road today contains a number of relays. It’s a broad name for a switch in your car that has both an input and output circuit. It permits a small amount of current to manage high-current accessories in your vehicle. The relay eliminates the need for larger switches and more wiring to make these things operate.

A correctly operating relay utilizes an electromagnetic mechanism to adjust the switch to open or close the circuit or, in this case, make or break it. The majority of relays are small black square devices known as many relays or ordinary relays. So, in this post, we’ll learn what a relay is and how it works. Furthermore, how to test a relay with a multimeter if it’s defective.

What Is A Relay

In general, a relay is an electromagnetic switch. A coil, an armature, and a few contacts make up this device. When we deliver a low voltage signal across the coil, it transforms into an electromagnet and attracts the armature to itself.

The armature shifts from one contact to the other as a result. When the voltage across the coil is removed, the coil de-energizes and ceases to be an electromagnet. The armature now flips to the opposite side.

Normally Open (NO) and Normally Closed (NC) contacts are the two types of contacts available (NC). When the electromagnet is turned off (the coil is de-energized), the armature makes contact with the Normally Closed (NC) contact. When the electromagnet is operating, the armature makes contact with the Normally Open (NO) link (the coil is activated).

The armature is known as COM because it is the common point for both NO and NC connections (short for Common). The COM, NO, and NC terminals are independent of the coil, and the COM terminals alternate between NC and NO based on the coil’s energization.

How To Test A Relay

An automobile relay is similar to an electrically controlled switch. When you turn on any electrical accessory in your car, such as your wipers, horn, or lights, the current goes via the relay, which contains two sets of contacts that are close together to power the device.

A typical car relay consists of two circuits: an energizing coil-based circuit and a contact lever-based circuit. We’ll use the horn of a car as an example to further grasp how these work.

A four-pin relay is included in the horn of a car. The coil is attached to two of the pins that sit opposite one another. The other two joined to the horn by an open contact. To make identifying the power source easier, each pin will be assigned a unique number.

Current passes through the two pins attached to the coil when the horn button on your steering wheel is pressed. The electromagnetic field produced by this coil attracts a lever situated along the contact circuit. When the lever shuts the point of contact, allowing power to reach it, the horn is activated.

How To Test A Relay With A Multimeter

To test a relay, use one of two modes on a multimeter.

Mode Of Continuity Testing

The major goal of this test is to ensure that the coil is in good working order.

  • Set the continuity test mode on the multimeter.
  • Connect the coil terminals with the multimeter probes.
  • The coil is electrically closed if the multimeter beeps (or if there is any trace of continuity) (good).
  • The coil is open and damaged if the multimeter doesn’t beep. It’s better to replace the relay.

Use the second option if your meter does not have a continuity feature or does not show any signs of continuity for some reason. Unfortunately, testing a relay with this continuity method will not detect any reduced coil turns.

Mode Of Resistance

If you want to test a relay with an Ohmmeter, you’ll need to do some preliminary study. The nominal value of the coil resistance can be found in the datasheet. The model number, which is normally written on the protective cover, can be used to obtain its datasheet online. On the other hand, the coil’s resistance is usually less than 400 ohms.

  • Select the Ohmmeter setting on the multimeter.
  • Connect the probes to the coil’s two terminals.
  • Take note of the resistance reading on the multimeter.

The relay coil is good if the measured resistance matches the resistance specified in its datasheet. If the resistance is extremely low or extremely high, the coil most probably has short turns or is closed.

Difference Between A 4-Pin And A 5-Pin Relay

A four-pin relay controls a single circuit, but a five-pin relay changes power between two circuits.

4 Pin Relay

In a 4 pin relay wiring diagram, two pins (85 and 86) regulate the coil, while two pins (30 and 87) switch power on a single circuit. There are two different types of 4-pin relays: typically open and normally closed. An open relay will turn on the power to a circuit when the coil is engaged. When the coil is engaged, a normally closed relay will switch off the current to a circuit.

5 Pin Relay

Two pins (85 and 86) regulate the coil, whereas three pins (30, 87, and 87A) switch power between two circuits in the 5-pin relay wiring diagram. They have connecting pins that are both ordinarily open and normally closed. Power is shifted from the normally closed pin to the typically open pin when the coil is triggered.

Bad Relay Symptoms

As you might expect, if a relay in your vehicle fails, it can cause havoc with numerous electrical systems. Because the relay is tied to every electrical item in your vehicle somewhere along the line, practically any imaginable electrical system could fail.

This includes everything from your gasoline pump to your door locks, power windows, and air conditioning, among other things. They have an impact on practically every aspect of your car. It’s possible that when a relay fails, it’s only a matter of it becoming loose or unclean.

You may notice any of these symptoms if your vehicle’s relays start to fail.

1. Stalling Unexpectedly

If your vehicle’s ignition relay fails, you’ll experience unexpected stalling. This occurs because the ignition is cut off, and you can no longer resume combustion since the relay can no longer operate the electrical current passing to your spark plugs.

2. Start-Up Failure

A faulty relay will cut electricity, preventing your car from starting. There are no lights on the dashboard, and the electronics aren’t working. When you turn the key, nothing occurs. The car is completely silent, with no clicking or other sounds. That could potentially be a dead battery, so you should check your battery and try jumping it off first.

A defective ignition relay switch can be identified by the failure to jump off. Most batteries, especially older ones, will easily discharge. It’s wise to have your battery tested anyway to rule out that possibility, as well as test your ignition relay switch.

3. Electric Smell

Ignition relays are susceptible to rust, corrosion, and water accumulation. This generates heat, which can melt or burn the switch or the plastic cover. A malfunctioning ignition relay switch will emit a burned-electronic smell. A malfunctioning relay switch might eventually harm your electrical system, so take your vehicle to a professional right away if you notice a burned odor.

4. Dimming Lights

Your headlight relay could be broken or malfunction, resulting in your headlights not operating at all or seeming dimmer than normal. This could be due to a faulty connection or overloading of the relay.

How To Test A Relay

The same thing can happen to the lighting in your vehicle’s interior or even on your display. As a circuit is overloaded or unable to sustain, you may experience intermittent dimming, lights not operating at all or flashing lights.

5. Windows Isn’t Responding

When you press the button on your power windows, they only drop and raise partially, become stuck, or don’t operate at all. This is a good indicator that the relay that controls your power windows has failed.

6. A Clicking Sound Is Made By The Starter

Relays are often all-or-nothing devices. Either the entire current is sent, or nothing is sent. Only a portion of the signal can be sent if the starting relay is destroyed. The starter relay clicks, but the engine does not turn, indicating that the starter motor is not receiving sufficient electricity from the relay. This could potentially be an indication of low or depleted battery power.

The relay doesn’t start working until it sends enough electricity to the starter. Smaller power may harm the entire starting equipment or cause the vehicle to fail to start, emitting an unpleasant clicking sound.

Corroded or aging relays with defective contacts can cause both of these problems. The only two alternatives for repair are to clean the contact points to guarantee proper flow or to replace the old relay. Sandpaper or a gravel scraper can be used to scrape the relay’s rusted surface. You can change the relay to acquire a bigger output, or you can consult a professional mechanic.

7. A/C Isn’t Working

When you switch on your air conditioner, If you notice that there is no cold air coming out, or no air coming out at all, it’s possible that your air conditioning system’s relay and control have failed.

As you can see, identifying the signs of a malfunctioning relay in a broad sense is difficult. You’ll have a better chance of identifying the symptoms of a bad ignition relay, a bad starter relay (which you can check by knowing how to tell if starter is bad, and get your car going again by learning how to jump a starter), a bad fuel pump relay, and so on because relays are connected to every electrical system.

To summarize, if any of your vehicle’s electrically powered systems aren’t working at all or are working at a reduced capacity, it’s quite likely that the relay attached to that device is the source of the problem. If this is the case, you might want to try testing a relay to see if there’s anything you can do.

How To Test A Relay

As the preceding description shows, relays are incredibly significant electronic components that allow low-powered devices, such as microcontrollers to control high-powered devices. Because relays are mechanical devices, they can break down with time, making sure they’re in good working order is important. If it stops operating, we must replace it right away.

But how to test a starter relay? There are several methods for determining whether or not a relay is functioning properly. We’ll look at a few different ways to test a relay, as well as how to test a relay with a multimeter.

How To Test A Relay Fuse Via DC Power Supply

The first way involves simply turning on and off the relay coil to determine if the armature switches between the two terminals. Connect the coil terminals to a 12V DC power supply or a battery with a switch if you’re using a 12V relay.

The circuit is finished and the coil is energized when we close the switch. The armature should now flip to a Normally Open contact. The armature should return to the Normally Closed contact if we open the switch. Because a 12V battery is commonly available, this is a handy approach for testing relays, particularly automobile relays.

How To Test A Relay Use A Circuit

We’ll build a modest circuit with simple components for the next technique and see if the relay works or not. This approach can be used to test relays in circuits and PCBs, but it can also be used to test automotive relays.

Assuming a 12V relay, we may switch it on and activate the coil by applying 5V to the transistor’s base. The armature contacts change position and light up the LED if the relay is functioning properly.

How To Use A Multimeter To Test A Relay

Finally, we’ll look at how to use a multimeter to test a relay. This is one of the most straightforward methods for testing a relay. Remove the relay from the circuit or the vehicle. Change the multimeter’s mode to Resistance Measurement (Ohmmeter). Set the range meter to the minimum range (200 or a similar amount) if you have a manual ranging multimeter.

Connect the multimeter’s leads to the coil terminals of the relay. The multimeter should read between 40 and 120 for a regular coil. If the coil is damaged or open, the meter will read out of range, requiring the relay to be replaced.

We may also use the multimeter to check for continuity between the relay’s three high-power contacts. The COM terminal must be linked to the Normally Closed (NC) terminal while the relay is in a de-energized state. However, the COM terminal shifts and makes contact with the Normally Open terminal as soon as the relay is energized.

To test this, set the multimeter to continuity mode and connect the multimeter’s leads to the COM and NC terminals when the relay is turned off. If the relay contacts are good, the multimeter should start the buzzer.

Now turn on the relay and check the COM and NO terminals for continuity. The relay is functioning properly if the buzzer sounds in both situations. If any of the tests fail, the problem could be a faulty relay.

How To Test A Fuel Pump Relay

Pull the relay out and physically inspect the terminals and socket for signs of corrosion and overheating before proceeding with the testing. Corrosion obstructs correct current flow, and overheating signals a problem with the relay or the circuits it connects to. If required, double-check the circuit.

Use an electrical contact cleaner to clean corroded terminals and sockets. Now you must determine which pins or terminals are part of the control circuit and which are part of the power circuit’s load or control.

You or the computer activates the control circuit of an automotive relay. The load or power circuit contains the activated load or accessory (fuel pump, radiator fan, headlights, horn).

Many automotive relays have a schematic stamped on the housing to identify each pin or terminal with a number. If you look closely at the real pins or terminals, you’ll discover that they all have the same numbers written next to them.

The terminals connecting to the control circuit are designated by the numbers 85 and 86, while the load or power circuit terminals are designated by the numbers 87 and 30. A common number system for these terminals on some smaller relays (micro relays) might be 1, 3, 2, and 4, correspondingly. They may, however, differ depending on the arrangement. For the correct terminals, compare the markings on the relay to the wiring schematic in your car repair manual.

Even so, you’ll come across relays that don’t have any numbers or schematics to help you figure out whose terminals they belong to. Consult your repair manual for wiring a relay or if you have accessibility to the underside of the relay’s socket, look for the thick and thin wires that connect to the socket.

Setting Up The Multimeter

The thick wires are connected to the terminals of the power circuit. The control circuit terminals are connected via thin wires. After you’ve located the terminals, make sure the power circuit terminals are connected.

  • Set your digital multimeter to the minimum range of the Ohms scale, or ‘continuity.’
  • Then attach one lead to one of the power circuit pins and the other to the other power terminal. The resistance on your meter should display infinite (OL, open load). You should not hear a beeping sound if you are utilizing the continuity setting.
  • Your relay’s power pins shorten if you detect 0 ohms or any resistance number in the hundreds or thousands of ohms instead of infinity or hear a beeping sound. Replacing the relay is necessary.

Relay Replacement Cost

The cost of replacing an ignition relay ranges from $15 to $100, depending on your car’s make and model and labor charges. The cost of an ignition relay ranges from $5 to $50, with labor costs ranging from $10 to $50.

How To Test A Relay

The ignition relay is often inexpensive, costing approximately $10 depending on whether you want to buy an OEM original or an aftermarket replacement. In many cases, replacing the ignition relay is also rather straightforward. If you want a mechanic to fix it instead, expect to pay between $15 and $100.


What Is A Relay

An electromechanical switch is referred to as a relay. It energizes the coil by controlling a circuit with a very low current. The coil creates a magnetic field that attracts a movable lever (pole) to change the switch position.

What Does A Relay Do

Relays are electronic and electromechanical switches that allow circuits to be closed and opened. It controls how circuit connections open and close in an electrical circuit. The relay is not energized with the open contact when the relay contact is open (NO). The relay is not energized if the contact is closed (NC). However, when energy (electricity or charge) is supplied, the states are more likely to shift.

How Does A Relay Work

The electromagnetic induction principle governs the operation of a relay. When a current is applied to an electromagnet, it creates a magnetic field around it. The DC current is applied to the load via a switch. Meanwhile, copper coils and iron cores operate as electromagnets in the relay. Then, the coil starts to attract contact when DC current is applied. This is referred to as relay energizing. When you remove the supply, it returns to its previous place. This is referred to as relay de-energization.

How To Wire Up A Relay

The number of terminals on a relay in the automotive world is either four or five, depending on the application. The layout of the relays is classed as type A or type B, and you must match the relay to your application. Each of the relay terminals has a distinct function and must be wired to a specific item. Typically, the battery positive, a ground, the trigger or switched power, and the powered item you want to activate will be wired in.

How To Test A Relay Without A Multimeter

This approach just determines whether or not the coil is operational. You will hear a “crisp-click” sound if you connect a 12 volt/9 volt/5-volt power source to the coil. This indicates that your movable contact is operational and that the relay coil is in good operating order.

Final Verdict – How To Test A Relay

Your vehicle’s relays are critical to ensure that all of your vehicle’s electrical components are functioning properly. Because there are so many of them, the most difficult step is typically determining which one truly controls the element of the car you’re interested in inspecting.

This is why you should always check your owner’s manual and keep it in a safe place, such as your car’s glove box. With the relay map, you’ll know exactly where to go and save a lot of time.

As previously said, relays are inexpensive. Moreover, the procedure of inspecting the relay will take only a few minutes of your time. This article will explain how to test a relay.

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