Service Brake Assist Light Comes On? Here’s Why And How To Fix

Does your service brake assist light come on while you are driving? Here's why it happens and ways you can fix it.

Emergency Brake Assist (EBA), or simply Brake Assist (BA), is a car safety system designed to reduce stopping distances in rapid braking situations.

If there’s a problem with the BA system or a supporting component, the message “Service Brake Assist” may display on the dash.

What causes the Service Brake Assist light to come on?

Here are the most likely reasons why:

  1. Faulty sensor
  2. Old or low brake fluid
  3. ABS/TC/ESC malfunction
  4. Bad electronic control unit
  5. Brake booster problem
  6. Wiring or signal fault

This guide examines these causes further. We’ll also cover what to do if the Service Brake Assist light appears. Finally, we’ll explain how to reset the BA system after addressing the cause.

But first, a quick look at how Brake Assist works.

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How Does Emergency Brake Assist Work?

Emergency Brake Assist
Image credit: Mercedes-Benz

Simply put, if Brake Assist senses the brake pedal pressed with enough speed and force, it increases hydraulic pressure to maximum. This means drivers need only press the pedal a short distance for full stopping power rather than all the way to the floor.

There are two main types of BA systems, mechanical and electronic, though only the latter is still used today. Design specifics vary from one automaker to the next, but all work similarly.

Learn more about how Brake Assist works in this YouTube video from The Engineer’s Post

6 Causes For The Service Brake Assist Light Appearing

#1. Faulty Sensor

Car Sensors

Brake Assist uses several sensors, which vary on the vehicle’s make and model. These measure hydraulic pressure, wheel rotational speed, and even the positions of the brake and accelerator pedals.

If a critical sensor fails, it can prompt the system to display a Service Brake Assist light on the dash.

#2. Old Or Low Brake Fluid

low brake fluid

Once the Brake Assist system detects rapid braking, the master cylinder will pre-fill the brakes with hydraulic fluid.

Yet, if the car’s brake fluid is low, the system can struggle to build enough pressure. In this case, a Service Brake Assist light, or another indicator, may appear.

#3. ABS/TC/ESC Malfunction

traction control light 1

Brake Assist works with other safety features, like Traction Control (TC), Electronic Stability Control (ESC), ABS, and more. In fact, some even share the same sensors to perform their tasks.

A problem with one of these systems can confuse the ECU, possibly causing the Service Brake Assist light to illuminate.

#4. Bad Electronic Control Unit

The electronic engine control unit of the car installed in the engine compartment. Car software

Another reason for the Service Brake Assist light coming on is a bad electronic control unit. Modern cars have 100+ ECUs managing their systems, including brake-related safety features like BA.

Further signs of a failing brake ECU include more dash alerts, the pedal getting harder to press, or feeling spongey, among others.

#5. Brake Booster Problem

Brake Booster

Brake boosters, also known as vacuum boosters or servos, “boost” braking performance by helping increase hydraulic pressure. This is done without the driver having to exert more force.

A problem with one of the brake boosters, like a faulty valve or vacuum leak, can lead to the Service Brake Assist light showing up.

#6. Wiring Or Signal Fault

Car Brake Line

As you may have noticed, Brake Assist is a bit complicated. The many components must communicate for the system to function.

An interruption, like a bad wire or fuse or a signal not transmitting, can result in the Service Brake Assist light appearing on the dash.

Is It Safe To Drive With The Service Brake Assist Light On?

No, driving with the Service Brake Assist light on is not a good idea.

Sure, it might seem like you have a small issue with a passive, seldom-used safety feature. However, after learning the various causes, you can see that a Service Brake Assist warning can actually mean some serious issues.

If you are unsure about the reason the Service Brake Assist light is illuminated, you will need to either go to a shop or figure it out on your own.

How To Fix The Service Brake Assist Light

Check The Brake Fluid Level

car brake fluid

Check the brake fluid level and condition when you see the Service Brake Assist alert.

Open the cap and add more if levels are below the minimum line. This might be all it takes for the dash alert to disappear.

If you can’t remember when you last changed your car’s brake fluid, or if it’s dark brown/black, you should consider flushing the system.

For the best results, most automakers suggest flushing the brakes every two years or 30,000 miles.

Scan The System For Errors

If your car’s brake fluid is fine, the next step is to scan the system for error codes using an OBD II scanner, which are handheld devices that plug into a car’s OBD port.

One error code, 01435, is associated with brake pressure sensor failure. There are many possible codes, like P0556 or P0577, which both concern brake booster problems.  

Yet, diagnosing the issue is not the same as performing the repairs. If you aren’t savvy under a car’s hood, consider calling a mechanic for certain tasks.

Reset The Brake Assist System

Service Brake Assist Light

If fluid levels are fine and a system scan reveals no issues, you should be able to safely make the light go away by resetting Brake Assist.

Resetting the light varies between manufacturers but disconnecting/reconnecting the battery is effective in most models. Just remember to drain the residual power in between by repeatedly pressing the brake pedal.

Otherwise, check your vehicle’s owner’s manual for instructions on resetting Brake Assist.

What Should You Do If “Service Brake Assist” Appears On Your Car’s Dash?

It is important to quickly deal with the reason behind a Service Brake Assist light for the sake of your vehicle, yourself, and your loved ones.

When safe, pull your car over and check the brake fluid levels. If below the minimum line, add more or call a tow truck.

For owners handy with an OBD II scanner, finding the cause should be simple. Just be careful not to tackle a repair you don’t know how to perform.

If you don’t yet own a code scanner, you can find them for as low as $30 at any reputable online auto parts store.

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Joshua Barrett

Josh Barrett is a writer hailing from the great state of Alaska. While describing himself in the third person is not his forte, writing about any and all things automotive – is. After 13+ years hustling in the exciting world of car sales, he took off to travel the world with his dog Teemo.