Posted by Matthew Yu on Thu, Mar 04, 2010 @ 05:40 PM
All vehicles are equipped with an anti-lock brake (ABS) systems that prevents the wheels on a motor vehicle from locking up while braking. An ABS is composed of a electronic control unit (ECU), four wheel speed sensors, and two or more hydraulic valves within the brake hydraulics. The ECU monitors the speed of each wheel and when it detects a wheel rotating slower than the others it then actuates the valves to reduce hydraulic pressure to the brake at the affected wheel which then reduces the braking force on that wheel. It works in the opposite manner for a wheel that turns faster than the others. This process is repeated continuously and can be detected by the driver through the brake pedal pulsation.
You should have your brakes bled when your brake system is opened to replace components such as calipers, wheel cylinders, the master cylinder, brake lines or hoses. Manufacturers usually specify that brakes should be bled every two years, starting from the date the vehicle was built. The most common bleeding procedure is to bleed the brake furthest from the master cylinder first, then bleed the other brake that shares the same hydraulic circuit. After these have been bled, you then bleed the other brake circuit starting with the furthest brake from the master cylinder. Typically, this would mean RR, LR, RF, then LF. However, it doesn't really matter if you start with the front or rear wheels, since they are on separate brake circuits on modern cars with ABS and/or dynamic stability control systems. However, you should start with the passenger side wheel and then do the driver's side.
Why must this procedure be done and how does it benefit you the driver?
- Fresh brake fluid has a significantly higher boiling point than old fluid, allowing harder braking without fade.
- That same moisture promotes corrosion. Frequent bleeding with fresh fluid allows brake components to last longer.
- A well maintained brake system could help you avoid ever having to replace calipers, master cylinder or an expensive ABS control unit.
- The bleeding process, done properly, removes air bubbles from the hydraulic system resulting in better brake pedal feel and more responsive braking performance.
- Too much air in the system can be dangerous and result in the pedal sinking all the way to the floor. Air is compressible while brake fluid is not.
Volkswagen has made it even simpler for you by providing this procedure to been carried our by a diagnostic scan tool! Below you will find the instructions on how to process the ABS Brake Bleeding with screenshots from the AUTOBOSS PC Max scan tool:
1) Select "03 - ABS Brakes"
2) Then "Introduction to Basic Settings - 04"
3) Enter Group 001 (Golf, GTI, Jetta, and Audi TT) or 002 (Passat and Audi A4/S4, A6/S6, and A8/S8)
4) Click "Go"
This will trigger the ABS pump to turn on for about 10 seconds. You should hear the fairly loud pump clicking during this time.
Click the "Done or Go Back" button and you're all set!