battery light on in car

Battery light on in car? Explained in easy to understand details

Battery light on in car

Is your battery light on in the car? The moment that your battery light came on instant fear pass through your body as you are reminded of the sometimes ridiculous price car owners pays to fix their vehicle. A bad alternator is one of the most common problems that can occur with a car that is growing in miles and years. If you are experiencing a battery light comes on and off

A bad alternator is another possibility, and another possibility is an electrical short which will set you back a few bills if either needs to be repaired. Don’t panic, the most common problem related to a battery light staying on is a bad generator AKA the alternator.

Since the alternator is what controls the electrical system of your car, a bad alternator is known to ruin other electronic accessories inside your vehicle if not repaired in a timely manner.

The main problem with driving with a bad alternator is if the problem is the bearing and the pulley gets hot enough it can melt the internal components of the alternator bind up, and break the serpentine belt and other engine components.

Symptoms of a bad alternator

Normally the signs of a bad alternator are the battery light comes on and stays on, however, once you accelerate and get higher in the RPM range, the failing alternator will kick in and out intermittently and the battery light will go out. Due to the acceleration, the alternator works faster and gets it moving again but don’t think for one second that everything is ok the alternator is on its way out.

Yes, a bad alternator can run down a battery

Symptoms for a bad alternator are similar to those of a bad battery.

A bad alternator can prevent a car from starting because it did not recharge the battery when the car was going through its normal drive cycle.

Obviously, batteries sometimes fail on their own but a bad alternator can actually cause the battery to drain because it’s lost the ability to recharge the battery.

A bad alternator can cause a number of engine symptoms, like not providing the right amount of voltage or too much voltage to the transmission and engine sensors making them behave erratically.

“YES”, a low battery or bad alternator can cause the airbag light to come on.

Signs of a bad alternator are pretty simple, continue reading to see what to look for in a failing charging system.

Another related symptom of a bad alternator is a car engine running weakly and then powering up again.

The proper step to diagnosing a bad alternator is starting with a charged battery. Drive the car for a long period of time and observe if the battery voltage drop until the lights dim and the accessories no longer function.

How to test a bad alternator

Keep in mind that a bad battery can kill an alternator, and a bad alternator can kill a battery, so if it’s either one, you may want to inspect both very carefully.

The best method of testing a bad alternator is with a voltmeter or multimeter. Don’t be worry too much these two are actually very simple to use.

car battery voltage test

With either tool, start the car and let it idle. Place multimeter or voltmeter on the voltage setting and touch the red wire to the battery positive terminal. Touch black wire to negative side of the battery all while the car is still idling.

Have a friend for family member turn the air condition to the highest setting, and head light high beam on all at the same time. Observe the multimeter for a drastic drop in voltage from 10 volts and lower. Also, watch for a change in engine RPM.

For future reference, a little trick to test for a bad alternator is to start the car (jump if necessary) then pull the negative cable from the battery. If the car dies after removing the negative cable, it is a good indication your alternator failed. 

How to prevent your charging system from failing without you knowing

The best way to prevent being stranded by a bad alternator is by having it tested on a regular basis. When you go in for your routine maintenance such as oil change, tire rotation, and many other forms of maintenance. Just ask to test battery and charging system and give you a printed report if possible.

If you’ve followed the steps above and concluded that you have a bad alternator if you are a do it yourself, remove the alternator and have the auto parts store test it for you to be certain the alternator really failed.

About Author

Collin Whittaker

My name is Collin and I am the editor and founder of My Used Car Blog. A little bit about my background - I've been an automotive technician for 10 plus years and I have worked for companies like Honda, Nissan, and other major automotive repair shops. I am a husband and a dad to three beautiful kids. My reason for starting this blog/website stems from my love and passion for the automotive industry. I will provide expert and insightful information from my years of experience.
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