How to Test a Relay

Auto Mechanic Using a Digital Multimeter

A starter relay, also known as a starter solenoid, is an electromagnet within a car’s internal combustion engine, used to help start the motor. Because this part is such a crucial element for connecting battery power to the starter motor, it’s important to understand how to test a starter relay when issues arise. Discover the tools and steps necessary to perform this task with Gateway Cable Company.

How Do I Know if My Starter Relay is Bad?

Your starter relay may be experiencing some issues if you notice the following signs:

  • Your engine won’t start after turning the ignition key
  • While turning the ignition key, you only hear clicks without an engine start
  • You experience intermittent starts, forcing you to turn the key multiple times during use

Once you’ve ruled out whether your car battery itself is dead, there are still many reasons why these issues may occur. Testing your starter relay is a good place to start narrowing down the problem.

Testing a Starter Relay

Luckily, starter relays are located in a very accessible part of the engine bay, meaning you can work on it without lifting the car. You will need the following tools for your assessment:

  • A digital multimeter
  • Wire

It’s also helpful to have someone ready to help turn the ignition while you perform your tests.

Step 1: Test for Electrical Resistance

Using your multimeter, place probes on both the ground lead and ignition circuit terminal. If the reading is more than 5 Ohms, your starter relay needs replacement. You can also use a wire jumper to check for resistance. Connect wire between the ignition circuit lead and the battery lead to see if there is a strong click. Weak clicks indicate that the starter relay is faulty.

Step 2: Test for Voltage

Switching your multimeter to 20V DC, connect the red probe to the terminal connection of the battery’s red wire, while placing the other on the black and white ignition switch circuit. When your assistant turns the ignition, the voltage drop should not be more than 0.2 volts. If so, you have an electrical conductivity issue and need a new starter relay.

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