How To Use A Multimeter On A Car: The Complete Guide

Modern cars use so much more electrical equipment than they used to. Because of this, we need to know if something electrical is failing. But in order to do this, we need to know how to use a multimeter on a car. 

This useful gadget can be used to check several electrical problems in our vehicles, saving us an expensive trip to the garage. If you know how to use a multimeter on a car, you can figure out what’s gone wrong and how to put it right.

But if you don’t know how to use a multimeter on a car, then you have come to the right place.

Finding The Problem

Electrical issues are often the most difficult to solve on a car. But a multimeter can really make the difference. Multimeters are special electrical tools that work by connecting probes to wires.

They are often digital and can help you figure out if a piece of electrical equipment in your car isn’t working. Electrical faults in vehicles are often because of a defective wire. Which your trusty car multimeter can help you track down.

A faulty wire will have a lack of voltage running through it. Which will be displayed on your multimeter’s screen. However, it can be a tedious process to check each wire until you find the culprit.

Three Different Checks

There are three main things you might want to check on your car (which also determines the settings you need to use on your multimeter). These are:

  • Voltage
  • Amperage
  • Ohm

Here’s a bit more about each one, and we’ll explain how to use them to check a few potential faults on your car further on in this article.

The first thing is the car battery voltage test. This will indicate whether electricity is getting to the piece of equipment you are having trouble with.

If your voltage check indicates that electricity is passing to the faulty piece of equipment, it’s time to move on to the next check – amperage.

The amperage check can identify whether an electrical charge is flowing through the faulty equipment. The voltage has shown electricity is getting there. But there may be a problem inside. For instance, a faulty lightbulb.

If there is no reading when checking the amperage of a piece of equipment, it means your circuit is unable to be completed. If the amperage and voltage signs are just fine, you can check the ohm reading. Otherwise known as the resistance.

The ohm reading is an indication of how difficult it is for electricity to pass through a circuit.

The lower the reading, the lower the resistance in your wires and circuits. This means it’s easy for electricity to flow through. 

Wires and circuits with a higher resistance mean your battery will work harder to pump the juice through the system to make your equipment work.

How Do I Test A Car Battery With A Multimeter?

One of the most common reasons why a car won’t start is the battery. Testing your battery is something you can easily do using a car multimeter. 

To test for voltage, first set your multimeter to the 20V setting.

This is the correct setting to check battery voltage because they are typically 12V batteries. Setting your multimeter any higher means you may get an inaccurate reading.

You can check your battery by connecting both probes to your battery’s terminals with your engine turned off.

The red lead is positive, which needs to be hooked up to the corresponding positive terminal on your car. The black is negative, and should also be matched to the terminal of the same colour.

If your reading is below 12V it’s a good sign that your car battery will need replacing sooner rather than later. 

Many batteries will run between 12 and 13 volts when the car is turned off. And this could rise to as much as 15V when the car is on and the charging systems are in operation.

How To Use A Multimeter On A Car Alternator

You may have realised that your battery is just fine. But you are still having an issue with your car’s electrical performance. 

It could be that your battery is failing to recharge thanks to a faulty alternator.

The alternator uses the mechanics of your car while in motion to recharge the battery. A failure to do this can result in a drained and lifeless battery.

Checking the alternator actually requires you to connect your multimeter to your battery once more. 

You can check how your car battery’s voltage responds to various electrical loads to see how well your alternator works.

With your vehicle turned off, connect your car multimeter’s probes to your battery once again. Hopefully, you will see a healthy reading of over 12V.

Turn your car on and you should notice that the multimeter’s reading has jumped to over 14V. If your reading is under this number with your vehicle turned on, your alternator is the problem.

If you have a reading of over 14V on your multimeter, it’s time to start putting your alternator through its paces. Begin to turn on your lights, heaters, and stereo to see if your alternator responds well or not.

If your battery’s voltage reading is dropping below 13V while these pieces of equipment are in use, you have an alternator problem.

A reading above 13V means your problems lie elsewhere.

How To Use A Multimeter On A Car Fuse

Multimeters can even check for blown fuses – all you need to do is switch your device to the ohms setting. 

Place your probes on either side of your fuses and check the reading. 

A low number on your display means your fuses are working just fine. However; no reading at all means your fuses have blown.

Our Final Thoughts

You may worry that using a multimeter on your car battery isn’t safe. But there are generally only small levels of voltage involved. 

However, we would like to note that if you own an electric vehicle we wouldn’t recommend testing your battery voltage yourself. This is because EVs run on a super high voltage that is high enough to put your life at risk.

If you own an electric car or vehicle, we would suggest bringing it to a garage to have a professional check it out.

Another useful piece of advice is to ensure you always zero your multimeter between measurements. This is because you will likely be measuring such low electrical readings that your results may be inaccurate with any residual reading on the multimeter.

We would advise using a digital multimeter when checking electrical components rather than one with a dial. Those multimeters that use dials can overload your equipment.

Correctly knowing how to use a digital multimeter on a car battery can save you time and money by diagnosing a faulty battery in minutes.

Thankfully, using a multimeter on your car is relatively simple. But, remember to always connect red on red and black on black. 

Now that you know how to use a multimeter on a car battery, you can save yourself time and money by diagnosing electrical faults without a trip to the garage.

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