When you notice the battery and brake light on simultaneously, your car system has a complicated issue. Normally, modern cars are equipped with various sensors to monitor the functionality of several car parts. And when these sensors obtain information from various systems, they send the signal to the Engine Control Unit (ECU) for interpretation. When the battery light illuminates on the dashboard, the ECU is informing you there is a battery charging issue. On the other hand, when the brake light illuminates, the ECU is telling you there is a problem with the brake system. But what if you see the brake light and battery light on simultaneously? Then you have a faulty alternator, malfunctioning brake system (together with electrical components like sensors), dead car battery cells, faulty voltage regulator, loose wiring, and other causes. Let’s learn more about the causes in the next topic.

Brake And Battery Lights Activates Simultaneously: What’s the Issue?

All the dashboard lights will illuminate when you turn on the car. But they all turn off after the car runs for a few minutes. What if the lights don’t go off? Your car has some serious problems that need to be fixed. Below is what causes the brake light and battery light to come on at the same time:

1. Faulty Alternator

Many times car owners have contacted me. “Hey, my car battery and brake light on, and later the battery turned flat.” Normally, we test the battery after charging it and notice it’s in good condition. But when we get to the alternator, we see it’s dead.   Faulty Alternator :photo   Short circuits kill the alternator quickly. But also age can take a toll on this vital equipment that charges the car battery. And unfortunately, when it fails, the car battery light will illuminate due to low charge. On the other hand, some brake system electrical components like wheel speed sensors use power to function. The ECU will show a brake system problem if they lack enough power supply.

2. Damaged Alternator Belt

In another case, your alternator may not be faulty, but its belt may have aged and started cracking. And once the belt slides or fails to spin the alternator at the required speed, it fails to fully charge the battery and supply the maximum power for other components. In this case, you’ll learn your car check engine brake and battery light on due to low power supply. Damaged Alternator Belt :photo

3. Dead Car Battery Cells

Your alternator may function normally, but your car battery cells may be dead. What happens afterward? All power comes to the battery before being distributed to various components. So, if the battery cells are damaged, your system may show brake and battery lights. A faulty alternator, short-circuiting, extreme temperatures, and aging battery are the leading causes of dead battery cells.

4. Corroded Battery Terminals

Many a time, it has happened. The alternator and the battery are in good condition. But the battery has gone without service for an extended period. Note that corroded terminals don’t mean the battery is dead. However, the battery will not charge or power components effectively. Corroded Battery Terminals :photo

5. Faulty Wiring

Loose wiring or shorted wires can ruin all the car computer system functionality. They alter the signals from wheel speed sensors connected to the brake system and the battery cells. This results to error signals on the ECU, and the brake, the battery, and other lights may turn on.

6. Accessory Overload

This applies to many gearheads. You plan to go tracking, and the car sockets are loaded with many accessories. You aren’t enjoying; you are killing the car battery and the car functionality. See, aftermarket stereo systems, complex car alarms, tracking devices, and charging phones on the dashboard can cause electric overload. These accessories will require alot of power, and several vital car components will lack the power to operate. This turns the battery and the brake light on. Later the wires may overheat and fail.

7. Low Brake Fluid

A leaking brake fluid pipe or a low brake fluid can cause the brake light to turn on. And if there are other battery issues, both lights may appear on the dashboard. This can cause too much confusion, especially if you try to check the system at home.

8. Parking Brake Not Fully Disengaged

Oh! You may ruin your car brake system if you are that forgetful person. Several drivers often don’t fully disengage the parking brake when driving. As a result, the brake light remains on, and the engaged parking brake can damage the brake system and cause other car components to strain when moving.   Parking Brake Not Fully Disengaged :photo  

9. Worn Out Brake Pads

When you apply brakes, worn-out brake pads cause the caliper pistons to move deeper into the rotors. This makes the brake fluid go low, and as a result, the brake light turns on. The worst may happen if there are other electrical system issues. Both brake and battery lights will illuminate.

10. Faulty Anti-Lock Brake System (ABS)

Electrical wiring issues and dirty wheel speed sensors are the main cause of Anti-lock brake system failures. As a result, the battery light may turn on due to electrical failure, and the brake light will turn on due to the faulty mechanical system.

11. Malfunctioning Voltage Regulator

The voltage regulator controls the voltage generated by the alternator. If it fails, there may be high voltage in the electrical lines. This can result in battery failure and malfunctioning of other components. And you’ll see the battery light turn on while driving.   Malfunctioning Voltage Regulator :photo

What To Do When Your Brake and Battery Light Comes On

If you notice the battery and brake light flashing while driving, park the car and check before visiting the mechanic. Here are a few things you can do with basic knowledge:

Examine Your Alternator, Battery, Voltage Regulator, And Wiring

Start by smelling around the car to feel if there are shorted wires. Then, check the alternator belt and test the voltage using a multimeter. Here is a guide for testing the alternator, battery and voltage regulator. Step 1: Connect the multimeter to the battery terminals and check the readings. You should get 12.5V to 12.8V when the car engine is off to know the battery is in good condition. Step 2: Turn the engine and connect the multimeter to the battery terminals to check the readings. If it reads 13V to 13.5V, all the components are functioning well. Step 3: Turn on the headlights and the radio and test using a multimeter. The reading should be 13 to 13.5V.   test using a multimeter :photo   A lower reading will indicate the alternator is faulty, while a higher than 13.5V will mean the voltage regulator is releasing high voltage. Visit the specialist to have the issue fixed. Also, if the battery terminals are corroded, clean them and apply silicone grease to prevent further corrosion.

Minimize Electrical Accessories Plugged Into the Car

Avoid overloading the electrical sockets. You can charge some accessories at home and preserve the power for vital car components.

Disengage the Parking Brake

Always ensure the parking brake is fully disengaged before driving your car. This will save the brake system and other components from much pressure.

Inspect the Brake System

Inspect the brake fluid pipes, brake pad condition, and wheel speed sensors and have them fixed by a specialist. Note that dirty sensors can cause the brake and battery light to illuminate.

Frequently Asked Questions (FAQs):


What Should I Do When These Warning Lights Come On?

Suppose you notice the battery and brake light on while driving; stop the car and turn off the engine. Secondly, get under the car and check for any brake fluid leaks. Go around the car and smell for any shorted wire smell. Else, take a multimeter and test if the battery, alternator, and power regulator are in good condition. If there are complicated issues, call a mechanic but if the car can drive, go to the nearest mechanic and have it diagnosed.


Can I Drive With the Brake and Battery Lights On?

You should consult a specialist before driving a car with the battery and brake light on. If the specialist advises you to drive, it should be a very short distance to get to a repair shop. Else, ignoring the brake and battery lights may put you and other road users in danger if the car brakes or other electrical components fail.


Can a Bad Alternator Cause the Brake Light to Come On?

If the car alternator is faulty, it will undercharge the car battery. Afterward, the battery will supply less power to brake electrical components, and the battery and brake lights will turn on.


Can a Scanner Clear My Brake Lights?

If you have fixed the problems and the brakes lights dont go off, a scanner can help to detect and fix electrical errors. Note that the lights will go off if the issues are completely fixed.

Our Final Notes

Once you notice the car battery and brake light on, know there are either complex electrical or brake issues. Park the car and do some checkups before calling the mechanic. If your mechanic advises you to drive to the repair shop, drive carefully to avoid accidents.