2008 BMW 650i Brake Pressure Sensor Replacement Cost

Automotive braking systems are responsible for stopping extremely heavy vehicles through the use of hydraulic pressure. Since the braking system must stop such a heavy load, the hydraulic pressure operating the brake system must be extremely high. But what happens when brake pressure starts to decline because of a deficiency in the system? To monitor the brake system operating pressure through the entire range of brake pedal movement, a brake pressure sensor is used to constantly report the amount of brake pressure present in the master cylinder, ABS hydraulic control unit, or individual brake lines at all times. This allows the vehicle's computers to catch a brake pressure failure before it leads to an accident.

The brake pressure switch is installed in direct contact with pressurized brake fluid in the braking system. It is also powered by the battery, ABS control module, or both. The power source is not as important as the signal the sensor sends to the ABS (or other) control module. The signal sent back the the control module will allow the control module to understand how much pressure the brake pressure sensor is subjected to at all times. Since the control module will have a digital map or table of what the pressure should be, when the pressure is outside of the normal range, the brake, traction control, and ABS warning lights will be illuminated. This allows the control module to communicate the error directly to the driver.

There are two scenarios to consider when discussing symptoms of failure for the brake pressure sensor. The brake pressure sensor may fail, but more importantly, the brake system may have a loss in pressure. Understanding the difference is key to diagnosing the vehicle as will be discussed. If the brake pressure sensor reports low brake fluid pressure, the brake, anti lock brake system (ABS), and traction control (TC) lights will illuminate, plus there is the chance of a brake fluid leak. Also, many manufacturers have trademarked names for the TC system, so they will have a different warning light for that system. Some examples would be: ESC, DSC, SH-AWD. However, if the sensor has failed, the reported pressure will be incorrect. The same warning signs will appear, but there is no chance of a brake fluid leak.

Braking systems are one of the most important systems on any vehicle. If there is any issue with the braking system, especially if warning lights are on or the vehicle's brakes feel odd, the vehicle should be serviced immediately.

Brake system pressure sensors fail at a much lower rate than most other components of a vehicle. In fact, many people are unaware that their vehicle, or even their last vehicle even has one of these sensors. They are exposed to heat that travels from the service brakes through the lines, but otherwise they have no regular cause of failure. They should last the lifetime of the vehicle, and then some. Any failures are random, at best, or from physical damage.

When a technician enters a vehicle with an anti lock braking system (ABS), traction control (TC) of some kind, and theses systems have warning lights on, the first thing that technician will think is that the problem is not the typical wheel speed sensor. That is because the 'BRAKE' warning lamp will be illuminated. First, they will set and release the parking brake, to test for normal operation, then, a professional grade scanning tool will be used to read fault codes for the ABS control module. There, the technician will see fault codes indicating brake pressure is incorrect, and he or she will proceed to view the operation of the sensor. If the sensor is reporting information correctly, the brake system will be diagnosed for pressure loss or leaks.

If the brake fluid pressure sensor is at fault, the technician will either remove the sensor by unscrewing the sensor from its mounting location or disconnecting brake lines running in and out of the sensor. Most commonly, the brake pressure sensor will be mounted on the master cylinder or the ABS hydraulic control unit. Once removed, the new sensor can be installed and connected electronically. Depending on the location, the brake system, including the master cylinder, may have to be bled of air before the technician may test the operation of the brakes and new brake pressure sensor.

If the manufacturer specified maintenance calls for flushing the brake system, now is a good time to have that done under one of two conditions. That is, if the interval for completing the service is coming up very soon, or the maintenance interval has elapsed. If the service has been done on time, or it is not due for quite some time, skip it to avoid an unnecessary charge. In the event the owner's manual does not suggest a mileage or age to flush the brake system, there are scheduled maintenance lists for most vehicles on RepairPal.com.

Many vehicles will not have a brake pressure sensor, especially older vehicles and those without anti lock braking systems. If the brake warning light comes on in an older vehicle, it is most likely that air has been introduced into the master cylinder, the master cylinder has failed, or the parking brake switch or brake light switch is defective. Knowing which system you have on your vehicle is extremely important when attempting to diagnose the braking system. This is because the older systems use simple electric circuits, while newer vehicles use electronic (computerized) circuits.

This can be a very easy or very difficult job, of course depending on component location. The other aspect is having the appropriate scan tool to determine if the sensor or the brake system is at fault. If the sensor is blamed when there is a hydraulic issue, the problem will return immediately. In the case of physical damage to the sensor, replacement can be done by someone who has a strong understanding of brake hydraulic systems, otherwise, leave this to a professional for diagnosis.