Troubleshoot Relays | OhmCheck.com

How to test electrical relays Test Procedures

Summary: Use these tips to test relays for cars, electronics, or appliances.

Relays are a small, most often hermetically sealed component that transfers power from one set of internal contacts to another. When in its simplest form, it is a switching device. A relay has a coil inside that when energized, will "actuate" the relay contacts and transfer the current through to the other side.

The internal coil has a power input and a ground. It takes both the power and ground to operate. Most relays will either be waiting on a power input or a ground connection.

Some relays will have multiple sets of inputs/outputs. Half the contacts will be "made" with the relay de-energized, and the other half will be "made" while the relay is actuated.

When troubleshooting relays you should find out what the coil resistance should be. You might find this in the manual of the component the relay goes to, or by researching the internet.

Now find the two contacts of the coil (usually contact numbers x1 and x2), and put your meter leads on the contacts. In the Ohms setting on your meter, you should read the resistance through the relay coil, if you get no movement or infinity Ohms, then the relay is open (coil windings are broken).

If you get zero Ohms or a lot less Ohms than the correct amount, then the relay coil is shorted. Either way the relay would need replaced.

Car Relay Type Car Relay Power Relay Type power relay

Another way to test a relay is by shaking it near your ear, if you hear the internals noticeably rattling, then the relay is most likely bad and needs replaced. Note: Some movement inside is common, when a relay is bad, it will sound like a bunch of pebbles knocking around.

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