How to Test if a Relay is Good or Bad?
2 Answers
Methods to test the condition of a relay are as follows: 1. Without powering the relay, use the resistance mode of a multimeter to measure whether the contacts (output terminals) are conducting. If they are conducting, it indicates the relay is damaged and needs to be replaced. 2. Connect the relay into a circuit to make it operate. Then, use the resistance mode of the multimeter to measure the resistance at the output terminals. If the resistance is very low (close to 0), it is normal. If the resistance is infinite or exceeds the standard value, it means the relay is faulty and needs replacement. 3. Use the resistance mode of the multimeter to measure the resistance between the normally closed contacts and the moving contact. The resistance should be 0. If the resistance is high or unstable, it indicates poor contact at the contacts.
As a seasoned veteran with years of car repair experience, I prefer testing relays myself as it saves money and is quite fun. First, ensure the vehicle is turned off and disconnect the negative battery terminal to prevent short circuits. Then locate the relay, typically found in the fuse box under the hood or inside the cabin. Remove the relay and carefully inspect its exterior for signs of burning, deformation, or cracks—these are clear indicators of failure. Next, use a multimeter to test the coil resistance: set the meter to the resistance mode and measure across the two coil pins. Normal values usually range between 50 to 150 ohms; an infinite or zero reading means it's faulty. Finally, check the contacts: energize the coil using a small battery or power source, then use the meter to verify if the output terminals properly open and close. If everything checks out, the relay is good; otherwise, it's time for a replacement.
