Why My Car’s Brake And Battery Light On At The Same Time?

Your vehicle is equipped with multiple sensors that monitor and ensure that all systems are functioning as intended. Whenever there is a problem with the brake system, your car’s brake and battery light on at the same time will let me know that there is a problem charging the battery.

What Does It Mean When Brake And Battery Lights On At The Same Time?

If the brake and battery light on at the same time, the alternator is most likely starting to fail. While it may still charge the battery, it might not be charging at the required voltage of at least 13 volts. Other possibilities include a fault with your braking system resulting in increased power consumption, a loose connection, or a faulty voltage regulator.

Possible Reasons Why Battery And Brake Lights Are On

I will cover in detail four main reasons that could cause your car to throw out these warning light simultaneously:

1. Failing Alternator

From my experience, whenever a customer comes in with his car having this problem, in most cases, it will be a faulty alternator causing the issue.

While you can test and diagnose the problem at home, I always recommend getting your car to a specialist as he will have the tools and knowledge required to fix it. However, I put together a short guide on how you can test your alternator at home using a voltmeter or a multimeter.

How To Test Your Alternator?

While it might seem like a difficult task to someone with not enough knowledge, testing your alternator can be easy. It is important to note that some alternators’ output will vary between 13 volts – 15.5 volts, depending on the car model.

Follow the steps listed below and you will be able to tell if you have a faulty alternator.

  1. Get your hands on a voltmeter
  2. Ensure your batterie’s terminals are clean
  3. Connect the voltmeter to the battery terminals
  4. You should be getting a reading of 12.5v – 12.8v while the engine is off
  5. Now start the engine and check for higher readings, ideally over 13 – 13.5v
  6. Turn on your radio, headlights and other electric components
  7. You should be getting around the same reading as before
  8. A lower reading will indicate that your alternator is undercharging the battery
  9. A higher reading will indicate that your alternator is overcharging the battery
  10. If the readings are off, I recommend visiting a car mechanic for a proper diagnostic.

2. Voltage Regulator Malfunction

Working as a mechanic for a long time has caused all sorts of problems with people’s trucks. On some vehicles, the battery and brake lights only flashed for a few seconds at a time. The voltage regulator has failed.

Simply put, a voltage regulator ensures that the maximum voltage flowing through the car circuit is the same. A faulty regulator will overload or overload the generator and cause the vehicle system to malfunction.

This may explain why you may see a battery light indicating a problem with the charging system and a brake light indicating that the brake system is malfunctioning.

3. Bad Contact Or Bad Wiring

Bad connection or bad wiring causes the ECU to simultaneously report a possible problem to the brake and charging systems.

Wires wear out over time, so it’s a good idea to check the battery harness. A damaged wire or a loose connection can cause a short and damage your car’s components.

It would help if you also made sure that the terminals of your battery were clean and the connectors were tightened.

4. Faulty Braking System

Although rare, there is a possibility that your braking system has an electric issue, causing the battery light to turn on too.

If every scenario discussed above fails, I recommend checking your brake lines’ wiring and ensuring they are not damaged.

Frequently Asked Questions

Here take a look at some frequently asked questions:

1. Will My Car Run With A Bad Alternator?

Short answer: “It depends”. The generator may be overcharged, overcharged or not working at all. In such a scenario, the car can be driven for a short distance until the car battery is discharged.

2. What Should You Do When These Warning Lights Come On?

If your brake and battery lights are on at the same time while driving, the first thing you should do is safely pull over for a quick inspection of your car.


If you find yourself in a situation the brake and battery light on at the same time. Find a safe spot where you can pull over and inspect your car.

Following a visual check, if everything seems fine, restart the car.

Even if the lights disappear after restarting the engine, it is still recommended to have the issue investigated by a car mechanic.

Leave a Comment