How to Identify a Faulty Car Relay and Troubleshoot It

Car relays play a crucial role in the reliable operation of numerous electrical components in your vehicle. From your horn to your headlights, a faulty relay can lead to various issues. This article will guide you through the process of identifying and troubleshooting a car relay. Whether you are a DIY enthusiast or a professional mechanic, this comprehensive guide will help you.

Signs of a Faulty Car Relay

One of the first signs indicating a problem with a car relay is the presence of clicks. If you hear clicks, it suggests that the relay is operating on one side – the side with the energizing circuit and coil. However, if there is no sound from the horn, it indicates a problem along the contact circuit.

Testing and Troubleshooting

Method 1: Relay Swap Test

Symptoms: If the device it's powering isn't working, swap it with another properly rated, known-working relay. If the device starts working, your relay is bad. If it doesn't start working, you likely have a different problem, probably and hopefully with the device itself.

Steps: Ensure you have a spare relay that is compatible with your vehicle. Disconnect the battery to avoid any accidental shorts. Replace the faulty relay with the new one. Check if the device works correctly with the new relay.

Method 2: Voltage and Continuity Tests

Symptoms: If the relay is a problem, you might notice no switching action, electrical noise, or the relay staying closed.

Steps: Remove the relay from the vehicle. Grab two 14-gauge wires with alligator clips on each end. Attach the wires to the relay according to the diagram on the relay. Connect the wires to the battery terminals. Listen for a click. If you hear one, the relay is working. A voltmeter will confirm the current flow.

Troubleshooting Symptoms of a Faulty Relay

Electrical Noise: This can be due to contact bounce or dirty contacts. Clean the contacts with a fine wire brush or sandpaper to ensure proper function.

No Switching Action: This can be caused by a burned-out coil or contacts or lack of coil voltage. Test the coil voltage using a multimeter to identify the issue.

Relay Stays Closed: This is typically caused by shorted or welded contacts. A visual inspection may reveal the issue, or you may need to replace the relay.

Additional Tips for Diagnosing Relays

Generic Symptoms: A faulty relay may exhibit several generic symptoms, including:

Good trigger circuit but no output activation. Inoperative component that bench checks as good. Circuits 85 and 86 check as good. Jumping relay cavity circuits 30 and 87 make the component work. Terminal tension is good on all relay cavities.

If none of these issues are present, it points to a relay fault. Refer to your car's service manual for specific wiring diagrams and relays to ensure proper troubleshooting.

Understanding and resolving car relay issues can significantly enhance the reliability of your vehicle. Whether you’re performing a swap test or engaging in more detailed electrical testing, this guide provides a robust approach to troubleshooting.