Caring for You Car: An Auto Service Website

Nobody wants their car to break down. To keep your vehicle running well, you need to provide it with regular service. Have the oil changed a few times per year, rotate the tires, and check and replace the brakes as needed. A good auto care service will take care of all these maintenance tasks for you. However, you may still want to know more about the processes they follow, when service is needed, and what other types of services may help your car last longer. We've build this website for people like you — responsible car owners who just want to learn more. Enjoy!

When Your Car Won't Start, Here's How To Tell Whether The Battery Or The Alternator Is At Fault


When your car's not starting, it can be difficult to determine whether the problem is with the battery or with the alternator. Your battery needs to be charged in order to start your car, and failing batteries often can't hold enough charge. Likewise, a failing alternator can't keep a battery at full charge.

How do you know which one is behind your car's electrical problems? Read on to find out how to narrow down the cause.

1. Use a Multimeter

If you own a multimeter or are able to borrow or rent one, using it to test your car battery is the easiest way to find out if the problem is with the battery or the alternator. Before you begin the test, you'll need to let the car sit idle for an hour. This allows any residual charge on the battery terminals to dissipate.

Set the multimeter to 20-volt DC mode, and then connect the red test lead on the multimeter to the positive terminal on your car's battery. Connect the black test lead to the negative terminal. Turn the multimeter on, and then note the voltage.

According to Haynes, a healthy car battery that's fully charged will give a reading of around 12.6 volts on the multimeter. When discharged, it will still read 12 volts. These numbers will vary slightly depending on weather conditions (they'll be lower when outside temperatures are freezing.) If your battery shows a reading of less than 12 volts, it's likely that one of the cells inside the battery has died, and it won't be able to provide enough power to start your car.

You can also use a multimeter to test your alternator. If your battery is discharged, you may need to have someone jump-start your car in order to start the engine. When the engine is idling and the alternator is functioning well, the voltage reading on the multimeter should be between 13.8 and 14.4 volts.

If the voltage reading is significantly higher than the 14.4 volts described above, it's a potential sign that your alternator is overcharging your car battery. This can cause it to explode, so you'll need to replace the alternator immediately. If the voltage reading on the multimeter doesn't change while the engine is running, then the alternator isn't charging the battery.

2. Use a Car Charger

If you don't have access to a multimeter, you can use a car charger to test your battery instead. Car chargers plug into a wall outlet inside your home and connect to your car's battery. Using a car charger allows you to charge the battery without relying on the alternator, which lets you isolate the problem.

Connect the car charger to your car's battery and wait for it to charge. Depending on the model, it may take up to 12 hours for the battery to fully charge. If your car won't start after charging the battery, it means that the battery can't hold enough charge.

If your car does start, you can test the alternator by letting the engine idle for 15 minutes. Turn on your car's headlights and radio in order to drain the battery. A functioning alternator won't have any issues with this electrical load. After 15 minutes, turn your car off and attempt to start it again. If it doesn't start, the battery isn't receiving any charge from the alternator.

3. Take the Battery to an Auto Repair Shop

Finally, it's not possible to test your battery or alternator if you don't have access to a multimeter or car charger. There's no way to tell if the battery won't hold a charge or if the alternator isn't charging it. Thankfully, most auto repair shops will test batteries and alternators for free.

Removing an alternator is usually a difficult task in most cars, but removing the battery is simple. You can remove the battery in your car and take it to an auto repair shop that has a battery tester. If the battery is bad, purchase a new one at the auto repair shop and install it in your car.

If the battery is in good condition, however, you'll need to have your car towed to the auto repair shop in order to test the alternator. Once there, you'll be able to know for certain whether or not the alternator is the cause of your car's electrical issues or if it's a more complex problem with the wiring or the starter.

Overall, testing your car's battery and alternator is easy if you have access to a multimeter or a car charger. If you don't, find an auto repair shop in your area that offers battery testing services. Bringing your battery to them is the first step in narrowing down what's causing your car to not start.


25 August 2020