Leave the air conditioner off, as well as the headlights and any other accessories.

Now that you have a baseline, it’s time to turn the engine on.

With the engine off, you should get a reading somewhere between 12.0 volts and 12.6 volts. Touch the positive side of the voltmeter to the positive battery wire.

With your Corolla turned off, you’ll connect the negative side of the meter to the negative battery post or wire.

Specifically, you’ll need to set it to 20V DC. The following was taken from bad alternator diagnosis page on this site: With a multimeter you do a quick test to see if your Corolla’s alternator is working or not. The first thing that you’ll want to do is get a good multimeter. If you have a voltage meter, that’s a fantastic place to start. You can diagnose whether your Corolla’s alternator is bad pretty quick at home. Just be careful not to get any of the corrosion in your eye. A battery post cleaner or wire brush can clean it up in no time. If the battery post is really corroded, it won’t be able to do its job of sending the voltage to and from the battery efficiently, and your Corolla’s battery light will turn on. The voltage from the alternator is sent to the battery through a wire that connects to the battery post. If the serpentine belt goes bad, it will no longer be able to turn your Corolla’s alternator enough for it to get an adequate charge. The serpentine belt turns more than one engine accessory (A/C compressor, power steering, etc). Nearly all modern vehicles use a serpentine belt to turn the alternator. See Also: Toyota Corolla Bad Alternator Diagnosis A new alternator will rectify the problem. If you see your Corolla’s battery light turns on while the engine is already running, that is a strong indication that the alternator is no longer providing enough wattage to power the various electrical systems and charge the battery at the same time. A bad battery usually makes itself known when you are trying to start the vehicle.Ī bad alternator will usually make itself known when the engine is already running. It can run off the alternator just fine once it’s started. The battery is primarily there to start your Corolla. There isn’t a lot to it, which makes diagnosing it relatively simple.

The engine turns the alternator, which charges the battery. The charging system in vehicles hasn’t changed that much in the last 50 years.

That would indicate a bad battery, but it’s still worth your while to have it tested first. You may have noticed your Corolla struggling to start, and then the battery light stays on after the start. With an older battery, you will often notice this on the first truly cold day of the year. Most battery lights will come on when the vehicle starts if the computer has detected that the voltage was too low for a quality start. The battery light comes on when it detects that the voltage in the battery is too low. It’s almost always going to be caused by a bad battery or alternator. The charging system itself is relatively simple. It is trying to warn you that there is an issue with the charging system. If your Toyota Corolla’s battery light is on, it means a few things.

Dashlights off on toyota cotolla 2016