What Does BAS Mean? Understanding Your Vehicle’s Brake Assist System

Reviewed by

Anthony Harlin, ASE Certified Master Automobile Technician

Technical Reviewer at CarParts.com

Written by CarParts.com Research Team - Updated on December 13th, 2023

Reading Time: 5 minutes
Summary
  • The ESP BAS light could indicate an issue with your electronic stability program (ESP) or brake assist system.
  • This warning light may be triggered by a malfunctioning steering angle sensor, a faulty brake switch, bad wheel speed sensors, or wiring issues.
  • While your vehicle will continue to run with an illuminated ESP BAS light, it’s best not to ignore it. Driving with a malfunctioning ESP or BAS system can be dangerous in rainy or snowy weather.

A triggered dashboard light is almost always bad news, so if you see one turn on, you’re going to want to put that high on your to-do list, especially if it’s your ESP BAS light.

What Does the ESP BAS Light Mean?

The ESP BAS light on your dashboard turns on when there’s an issue with your electronic stability program (ESP) or brake assist system (BAS). You’ll have to troubleshoot your vehicle to get an actual diagnosis, but here are some of the common causes for a triggered ESP BAS light:

Malfunctioning Steering Angle Sensor

If your ESP BAS light is on, then there’s a big chance that it’s all because of a failed steering angle sensor or it’s out of calibration. The steering angle sensor monitors your steering wheel, making sure it’s aligned with your wheels, so your vehicle can determine which way you’re turning.

A faulty steering angle sensor will likely send incorrect signals to your wheels and make it hard to drive. If this is what’s tripping your ESP BAS light, then it’s a good idea to fix it as soon as possible.

Faulty Brake Switch

Brake switches are typically made to last, but things don’t always go according to plan. Given how your brake switch goes into action every time you press down on the pedal, it’s all too easy for it to break from wear and trigger your ESP BAS light.

The brake switch is responsible for turning on your vehicle’s rear brake lights, which means a bad brake switch will likely fail to turn on your rear brake lights whenever you’re slowing down or stopping. This can lead to some serious traffic accidents, so you might want to fix your bad brake switch as soon as you can.

Your vehicle may have two brake switches: one for the brake lights and another for things like cruise control, body control systems, etc. Make sure you know which one you are dealing with if you have more than one.

Your vehicle may have two brake switches: one is for brake lights and other is for things like cruise control, body control systems, etc. Make sure you know which one you are dealing with if you have more than one.

Anthony Harlin, ASE Certified Master Automobile Technician

Bad Wheel Speed Sensor

Each of your vehicle’s wheels has a speed sensor, which monitors the wheel’s motion. Your vehicle’s ESP and BAS rely on these sensors to monitor your vehicle’s traction, so they can take appropriate action when your wheels start to slip.

The ESP BAS light typically turns on when your vehicle loses traction, but it should turn off once your vehicle regains control. If it stays on, then there’s a chance that your wheel speed sensor is the issue. Generally, however, a wheel speed sensor issue will turn on the anti-lock braking system (ABS) light first.

Wiring Issues

If any of the wires connected to your vehicle’s ABS short-circuits, you’re likely to find your ESP ABS light on.

Wiring problems aren’t common with most modern vehicles because of how well-protected the wires are, but it can definitely still happen and trigger your ESP BAS light.

What Does the Brake Assist System Do?

While your vehicle’s ESP consists of your vehicle’s traction control system, ABS, and other systems related to traction issues, your BAS is in charge of increasing brake pressure whenever you suddenly slam on the brake pedal.

It monitors the intensity, speed, and force of your foot when you step on the brakes, and once it detects a need for more support, it bypasses your brakes and applies even more pressure on your brake pads until your ABS kicks in and saves the day.

What Are the Advantages of the BAS?

Did you know rear-end collisions are the most frequent type of collision in the US? They make up around 29% of all car crashes, and they cause a number of injuries and fatalities each year too.

That’s why brake assist systems are so important. They help drivers avoid rear-end collisions by applying the brakes during emergencies.

Here are some other BAS advantages to consider:

Comes With a Brake Booster System

Most brake assist systems come with a brake booster system, which typically uses the engine pump or electric motor to lessen the amount of force you have to apply when stepping on the brake pedal.

A lot of modern engines with turbochargers also have a vacuum pump to help the brake booster.

Allows for More Braking

In emergencies, applying too little pressure on the brakes can mean life and death, and research shows that most drivers tend to hesitate when hitting the brakes. This is when the BAS can be incredibly helpful. The added pressure it applies on your brakes significantly lowers your vehicle’s speed and might even help you avoid a collision.

Adaptive Learning Technique

On some vehicles, the BAS comes with an adaptive learning technique that studies the driver’s braking patterns. That way, it can tell the difference between stopping after a daily commute or an emergency situation.

Can You Drive With the ESP BAS Light on?

Your vehicle certainly won’t stop running if your ESP BAS light is on, but it’s still a bad idea to ignore it. Driving around with a triggered ESP BAS light is a recipe for disaster, especially in rainy or snowy weather.

If the ESP or BAS lights are on solid, then this just means they are not going to operate, so you will not have that added security when driving. Braking is all on the driver with no help from the vehicle systems.

How To Reset the ESP BAS Light

There are a couple of things you can do to fix your ESP BAS light. For one, you can try replacing whatever faulty component is causing it to turn on. Of course, this also means you’ll have to troubleshoot and find the culprit first.

In some cases, fixing the steering angle sensor should do the trick. However, you’ll have to first have the ability to reset it with a scan tool that has that capability. Second, you have to make sure you have a quality part. Third, you should never replace a part without first scanning to see what the problem is and then confirming if the part in question is the problem or just where the computer sees the problem. The part named in a code description is not necessarily the problem.

You can also try fixing the sensors by turning your steering wheel. Here’s a general process:

  • Turn on your vehicle’s engine.
  • Turn the steering wheel two times to the right and then two times to the left.
  • Return the steering wheel to the center so your wheels face forward.

Your ESP BAS light should turn off after your steering wheel goes back to normal, but if it doesn’t work, you might have to recalibrate or replace your steering angle sensor. Sometimes, the answer to fixing your ESP BAS light could also be installing a new brake switch sensor or wheel speed sensor.

About The Authors
Reviewed By Anthony Harlin, ASE Certified Master Automobile Technician

Technical Reviewer at CarParts.com

Tony Harlin is a Master Gas and Diesel Diagnostic Technician with over 18 years of experience. He works full-time at a large independent automotive shop as a driveability and repair technician working on all types of vehicles with a focus on diesels. ASE certifications include A1-A9, L1 and L2, as well as X1.

Written By CarParts.com Research Team

Automotive and Tech Writers

The CarParts.com Research Team is composed of experienced automotive and tech writers working with (ASE)-certified automobile technicians and automotive journalists to bring up-to-date, helpful information to car owners in the US. Guided by CarParts.com's thorough editorial process, our team strives to produce guides and resources DIYers and casual car owners can trust.

Any information provided on this Website is for informational purposes only and is not intended to replace consultation with a professional mechanic. The accuracy and timeliness of the information may change from the time of publication.

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CarParts.com Research Team and Anthony Harlin, ASE Certified Master Automobile Technician