How to Test a Relay with a Multimeter (Step by Step Guide)
Relays are one of the most important electrical components in automobiles, home automation systems and other applications where fast switching of high power circuits is required. However, like electromechanical devices, relays are subject to wear and tear and can fail at any time. Thus, it is very important to test your relays regularly to ensure they perform at their best.
One of the various relay test methods is a digital multimeter. Let me walk you through the steps to get started testing a relay with a multimeter.
About relay
A relay is an electrical control device with a control system (input circuit) and a controlled system (output circuit), which are often found in control circuits. It functions as a circuit regulator, safety circuit and converter. The relay features fast response, stable performance, long service life and small size. (1)
Relays are typically used to control a high current circuit from a low current circuit. They are in almost every car. Relays function as switches, allowing a low amperage circuit to turn on or off a high amperage circuit. In addition, the relay can also control multiple systems at the same time, such as turning on the headlights when the wipers are on, or extending the antenna when the radio is on.
What You Need When Testing a Relay
Testing your vehicle's relay is a simple procedure that does not require the use of a complete kit. To start testing the relay, you will need the following items:
Tools:
- High impedance test light
- An ohmmeter, often referred to as a digital multimeter (DMM).
- Automotive Service Manual (optional but highly recommended)
Spare parts:
- Proper Relay Replacement
- jumper wire
Relay Test Steps
Step 1: Find the Relay
Depending on what it controls, you can find the relay under the dash or in the engine bay. Check the electrical chapter of your service manual and wiring diagram if you are unsure of the placement.
Step 2: Check and clean the connectors
Once you find the relay, remove it. Then clean and inspect the connectors while this relay is off. Replacing the main relay with a suitable replacement is the quickest and easiest way to test it.
Step 3: Get a multimeter
Set your multimeter to resistance measurement mode. Then measure the resistance by touching the coil contacts. The standard coil has a resistance of 40 ohms to 120 ohms. A bad solenoid coil winding indicates that the relay is out of range or open and it's time to replace it. Then keep the multimeter in resistance or continuity mode. After that, connect the switch contacts to the leads. It should show open or OL if it is a normal open relay.
Step 4: Turn on the electromagnet coil
With a 9-12V battery on the contacts, apply power to this magnetic coil. When the coil energizes and closes the switch, the relay should make an audible click. On a 4-pin relay, polarity is not important, but on diode relays it is critical.
Step 5: Connect the test lamp
Connect the battery positive to one of the switch terminals while the coil is still active. Then connect a test lamp between ground and switch terminal. The control lamp should consume electricity and glow. Then remove the positive jumper from the battery. The control lamp should go out after a few seconds.
Step 6: Checking the Voltage Relay
At the switch, check the relay voltage. Bad contact points can lead to voltage loss. Remove the test light and change the multimeter to DC voltage. Then connect the wires to the test lamp connectors or switch contacts. The reading should match the battery voltage.
Step 7: Check the switch
Check the correct resistance in the switch. The positive jumper must be disconnected and the solenoid coil must be energized. Then measure the resistance across the switch contacts with a multimeter set to ohms. Typically, an open relay should measure close to zero resistance when turned on, while a normally closed relay should measure open or OL when turned on.
Relay Testing Pro Tips
When working with relays, it is recommended to remember the following:
Avoid mixing and matching
When you have a bad relay that needs to be replaced, it's not a good idea to mix and match relays from other vehicle components or a random trash can in your garage. This can cause a short circuit or power surge that will damage your car's electrical system. (2)
Handle with care
It is extremely important to be careful not to drop the relay. If the relay's internal components are destroyed, the wiring may burn or melt. Also refrain from interfering with the operation of the relay.
Keep away from combustible gases
Do not operate relays or anything that requires electricity in areas where explosive or flammable gases such as gasoline or other fuels are present.
Read repair manuals
Check your vehicle's service manual (not your owner's manual) to identify and understand the wiring and relay system, even if you're already an experienced garage repairman.
Organize your tools
Prepare all the necessary tools in advance and put everything in its place. This will save you valuable time and allow you to focus on the current task without looking for tools during the process.
F.A.Q.
How much does it cost to replace a relay?
A relay can cost anywhere from $5 to several hundred dollars, depending on what it controls. Next up are ohmmeters, which cost less than $20 and come in a variety of shapes and sizes. Second, high impedance test lamps are a little more expensive, averaging $20 to $40. Finally, jumpers are inexpensive, ranging from $2 to $50 depending on the length of the wire.
What happens if I ignore a possible problem?
Ignoring a failed relay or installing any old relay that fits can cause serious problems. If the relay fails or is installed incorrectly, it can burn the wires and possibly start a fire.
I don't have an ohmmeter or test light. Can I still check the relay?
No. You only have two options if you're sure your relay is the problem, and both require the use of an ohmmeter, test light, etc. First, be careful and replace the main relay with the necessary tools. Second, if you don't have the tools to test it, you can hire a mechanic to check and repair the relay for you.
You can also check out other multimeter testing guides below;
- How to test a capacitor with a multimeter
- How to use a multimeter to check the voltage of live wires
- How to test ground with a multimeter
Recommendations
(1) control system - https://www.britannica.com/technology/control-system
(2) garbage - https://www.learner.org/series/essential-lens-analyzing-photographs-across-the-curriculum/garbage-the-science-and-problem-of-what-we-throw-away /
