[Solved] BMW ABS and Brake Light On

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Here is a list of tools I use every day at the shop. Let me know if you use them too in the comments!

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When it comes to diagnosing the ABS and Brake light, BMWs can have multiple issues. Some common issues are wheel speed sensors, low brake pads, low brake fluid, or electrical issues with the ABS module. Even low quality parts can cause issues. The rest of this case study will look at how a new part cause still cause issues with the ABS and Brake system.

What does the ABS light mean on a BMW?

The ABS light on a BMW stands for “Anti-lock Brake System”. The Anti-lock Brake System assists the driver by restoring traction to the tires in emergencies. The ABS uses wheel speed sensors to determine if a tire has lost traction and then activates to restore traction to the tire. Each wheel has to have a properly function wheel speed sensor in order for the ABS to work properly. High quality parts are a must for the ABS.

Case Study on a BMW with the ABS and Brake light on.

A 2016 BMW 3-Series came into the shop with an ABS and Brake light on. After a test drive, there were no noticeable drivability issues other than the lights being on.

The first step in diagnosing an ABS and Brake light is to read the fault codes that are stored in the ABS module.

The scan tool I’m using is the Snap-on Zeus. It’s a professional scan tool that can do a multitude of functions. If you wanted to read the ABS module in your vehicle, there are plenty of scan tools with this function that do not have the high price. Here are a list of scan tools on Amazon.

Just looking at all of the fault codes (in the picture above) in this BMW can be overwhelming, but the key take-away is finding the common issue. All of the fault codes deal with a wheel speed sensor and/or a signal from the wheel speed sensor. Specifically, the fault codes deal with the left rear wheel speed sensor.

The scan tool I use allows me to view each wheel speed sensor as I take the vehicle for a test drive. The next picture shows all except one of the wheel speed sensors working.

Left Rear Wheel Speed Sensor not working

Why would a wheel speed sensor not work?

Common issues with wheel speed sensors can be the sensor itself, a wiring issue, or a malfunctioning ABS module.

After a quick visual inspection of the wiring of the left rear wheel speed sensor, there were no broken wires found.

I decided to replace the left rear wheel speed sensor.

The owner of this vehicle actually wanted to replace both rear wheel speed sensors. So at their request, the rear wheel speed sensors were replaced.

Fixed right? Not really.

After replacing the rear wheel speed sensors, the ABS and Brake light came back on. I took a look at the fault codes and found both rear wheel speed sensors were setting the codes now, not just the left one.

Two codes appeared after the repair.

While the BMW was sitting still, I checked the wheel speed sensors to see if they were showing incorrect data. The picture below shows not only incorrect data, but some weird data.

Weird spikes of 186.41 MPH.

The BMW is still and inside the shop, and the rear wheel speed sensors are showing spikes of 186.41 MPH.

Extremely incorrect data is being shown.

The only explanation is incorrect wheel speed sensors.

Even though the parts used say they are compatible with BMW, it is apparent that they are not. Some vehicles, including BMW, are sensitive when it comes to electronic components. A new issue can occur when a low quality electronic component is installed. Always choose high quality electronic components.

After replacing the rear wheel speed sensors again with correct BMW brand parts, this BMW worked perfectly and the ABS and Brake light did not come back on. Fixed!

Below is a picture of all of the wheel speed sensors working properly.

Properly working wheel speed sensors.

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