How Do You Check If A Relay Is Bad?

How Do You Check If A Relay Is Bad?, <h1>How Do You Check If A Relay Is Bad?</h1> <h2>Introduction</h2> <p>A relay is an electromagnetic, blog, how-do-you-check-if-a-relay-is-bad, KampionLite

How Do You Check If A Relay Is Bad?


A relay is an electromagnetic switch that allows a low-power signal to control a high-power circuit. It is commonly used in various electrical and automotive applications to control lights, fans, motors, and other electrical devices. Over time, relays can become damaged or faulty, leading to malfunctioning circuits. In this article, we will discuss how to check if a relay is bad and identify common signs of relay failure.

Signs of a Bad Relay

Before going into detail about how to check if a relay is bad, it is essential to understand the signs that indicate a faulty or damaged relay. Here are some common signs of relay failure:

  1. Inoperable device: When a relay fails, the component it controls will stop working. For example, if a relay controlling a fan fails, the fan will not turn on when the switch is activated.
  2. Intermittent operation: A bad relay may cause intermittent operation of the controlled device. It might work sporadically or only under certain conditions.
  3. Audible clicking noise: Relays produce a distinct clicking sound when they operate correctly. However, if you hear rapid or continuous clicking sounds, it may indicate a bad relay.
  4. Burn marks or damaged casing: Physical inspection of the relay can reveal burn marks, melted plastic, or other visible damage. These signs suggest a relay failure.
  5. Burnt smell: When a relay overheats due to excessive electrical current or a short circuit, it may emit a burnt smell. This indicates a damaged relay that needs replacement.
  6. Electrical issues: A bad relay can cause electrical issues in the circuit it controls. These issues may manifest as flickering lights, dimming lights, or even blown fuses.
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Tools Needed

Before attempting to check if a relay is bad, make sure you have the following tools:

  • Multi-meter: A multi-meter is a versatile tool that measures voltage, current, and resistance. It is essential for diagnosing relay issues.
  • Screwdriver: Depending on the type of relay and its mounting, a screwdriver may be necessary to remove the relay from its socket for testing.
  • Replacement relay (optional): If you determine that the relay is bad, you may need a replacement relay to restore the circuit’s functionality.

How to Check If a Relay Is Bad

Step 1: Identify the relay

The first step is to locate the relay that you suspect is faulty. Depending on the application, relays can be found in the fuse box, control panel, or even integrated into the device itself.

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Step 2: Power off the circuit

Before performing any tests, ensure that the power to the circuit is switched off. This precautionary measure prevents accidental electrical shock or damage to the multi-meter and other equipment.

Step 3: Remove the relay

Using a screwdriver or a suitable tool, remove the relay from its socket or mounting. Take caution not to damage the relay or any adjacent components during this process.

Step 4: Inspect the relay

Visually inspect the relay for any burn marks, melted plastic, or other signs of physical damage. If any damage is found, it is highly likely that the relay is bad and needs to be replaced.

Step 5: Test the relay with a multi-meter

Using the multi-meter set to the resistance or continuity mode, it is possible to test the relay’s coil and contacts.

Testing the coil

To test the coil, connect the multi-meter leads to the relay’s coil terminals. If the resistance reading is within the specified range (as indicated by the manufacturer’s specifications), the coil is functioning correctly. If the resistance measurement is significantly different or there is no continuity, then the coil is likely bad.

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Testing the contacts

Testing the contacts involves checking for continuity. Set the multi-meter to the continuity mode and connect one lead to the common terminal and the other lead to each of the normally open (NO) and normally closed (NC) terminals in turn. When power activates the coil, the contacts should change state, resulting in a change in continuity. If the contacts do not change state or there is no continuity, it indicates a problem with the relay’s contacts.

Step 6: Compare results with specifications

If the tested coil or contacts do not meet the manufacturer’s specifications, it confirms that the relay is bad and needs to be replaced. However, if the relay passes all the tests and there are no visible signs of damage, it is likely that the problem lies elsewhere in the circuit.


Checking if a relay is bad requires a systematic approach and the use of appropriate tools such as a multi-meter. By following the steps outlined in this article, you can determine whether a relay is faulty or damaged, allowing you to take appropriate measures to rectify the issue. Remember to exercise caution while handling electrical components and always refer to the manufacturer’s specifications for accurate testing procedures.



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