All of your car’s electrical wiring is directly connected to multiple relays. These car relays perform particular functions. Likewise, all of these relays have special functions. If each of the relays stops working, then the associated part will be disabled or start malfunctioning. That’s why you need to know how to test a car relay with a multimeter and without it.Budget is always a major concern for professionals. If you want best multimeters under 100 dollars then you can also find them easily here.
| Quick Look: To test a car relay with my multimeter, I set it to measure voltage and check if it passes voltage through the normally closed points. If there’s no voltage, I know the relay is faulty. Next, I apply voltage and check for continuity between the normally closed points if the continuity breaks, I replace the relay. If I find carbon buildup, I clean the relay base before installing a new one. |
Before testing any car relay, you must know the usage of a multimeter. Here you have two types of multimeters, Analog multimeter, and Digital Multimeter. Digital multimeters have an LCD on which you can see the respected values in digits. Similarly, in analog multimeters, there is no LCD but a needle with a printed background chart.
A Quick Look
Car Relay Testing with a Multimeter: Quick Step-by-Step Guide
What is a Relay, and How does it work?
“A relay is an automatic electromagnetic on/off switch.” You can control it with an electrical signal. The electrical signal can be manual or from your car controller.
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If we talk specifically about a car relay and how to test a car relay with a multimeter, it has 5 terminals 85 and 86 for the power supply, and the remaining three are used for control signals. The 87A and 30 are Normally closed points, whereas 87 and 30 are generally open points. This is because when applying the voltage across power terminals, the normally open point will be closed and complete the circuit.
Steps to test car relay with multimeter
- First of all, open your relay or fuse box and do a physical inspection.
- If you don’t find anything fishy, then turn on the ignition switch. Still not seeing any change?
- Now it’s time to use your digital multimeter.
- Keep the ignition switch on and set your multimeter to Voltages.
- Now attach one black test lead to the body of the car and the other test lead to each relay output.
- The relay which is not passing voltages through the normally closed point is at fault. Congrats, you have found the faulty relay.
- Now take out the relay from the relay box and directly applies the voltages.
- And check continuity between normally closed points. If the continuity breaks, then replace the faulty relay.
- Another tricky thing that can happen is carbon on the relay base.
- Turn the ignition off and rinse the base of the relay box with a contact cleaner. When it completely dries, take the new relay and fix it.
- Your car is ready to fly.
Safety Guide
Wear the safety gear
Always make a habit that before starting any electrical testing, wear safety gloves and safety glasses. While testing relays and learning how to test a car relay with a multimeter, you don’t know which relay is passing current, so don’t touch the terminal naked-handed.
Don’t reuse
If you have found out that your relay is faulty, then don’t use any pre-used relay. Because most of the time, recycled relays cause a spark or disturb the whole car’s electrical wiring.
Multimeter calibration
Always make sure that your multimeter is well calibrated. The most common issue faced by automotive electricians is that their testing tools are used roughly. This rough usage can cause damage to internal circuitry. If you have dropped your multimeter, then you must check its calibration. The calibration checking is straightforward: measure the voltages in a nearly known power socket or check the continuity of any dead naked wire. If the results are satisfactory, then you’re good to go. If you’re a fluke lover then i have made a list of most precised fluke multimeters for you.
Read the user manual
If you don’t know anything about relay testing or cannot find the relay’s pinpoint location, then read the user manual carefully. Hopefully, you will find a list of solutions on it.
Direct looping
If you are stuck in some deserted place, you can directly jump the wires between normally open points of your relay base. And later on, after reaching your garage, you can replace the car relay.
Check the coil power.
Sometimes you see that physically the relay looks pretty well, but sometimes it starts missing. To check its coil power, you can check the resistance of the coil. If the resistance is more than adjacent relays, then you should replace it.
Importance of multimeter in your toolkit
In electrical troubleshooting, you rely primarily on electrical testers. If you talk about electrical testers, then a digital multimeter is best among all. Being an automotive technician, I always have DMM in my toolkit. You can easily test all your car issues regarding electrical wiring, spark plugs, batteries, audio system, and headlamps.
Which multimeter is best for car relay testing?
There is a wide range of multimeters available in the market. The best one is an auto-ranging digital multimeter. The selection of your multimeter depends upon your usage and ranges. If you’re a beginner, you can get a cheap one, but you need a True RMS multimeter for commercial use. Additionally, learning how to test a car relay with a multimeter is essential for automotive professionals and DIY enthusiasts, making a quality multimeter an even more valuable tool.
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In addition to this, keeping in mind an automotive electrician’s usage, I have made a list of the best automotive multimeters.
You will definitely not use your multimeter only for relay testing. Instead, you will grab the one which can perform battery tests. But unfortunately, you can not perform an on-load battery test with it. So, for on-load testing, you need specially designed car battery testers.
Conclusion
Testing a car relay with a multimeter has become an essential part of my routine when troubleshooting electrical issues. By following the steps I’ve outlined, I can quickly spot faulty relays and replace them before bigger problems arise. I always make sure my multimeter is calibrated, prioritize safety, and keep my car’s electrical system well-maintained to avoid future headaches.
FAQs
Q1: How do I know if my car relay is faulty?
To test if a car relay is faulty, use a digital multimeter. Set it to measure voltage and check if the relay passes voltage through the normally closed points. If it doesn’t, the relay is faulty and needs to be replaced.
Q2: Can I test a car relay without a multimeter?
While a multimeter is the best tool for testing car relays, you can also try bypassing the relay by jumping the wires between the normally open points. This is a temporary solution until you can replace the faulty relay.
Q3: What should I do if I find carbon buildup on the relay base?
If you discover carbon buildup on the relay base, turn off the ignition and clean the base using a contact cleaner. After it dries, replace the faulty relay with a new one.
Q4: How often should I calibrate my multimeter?
You should regularly check your multimeter’s calibration, especially if it’s been dropped or used roughly. To check, measure the voltage of a known power source or check the continuity of a simple wire to ensure it reads correctly.