Mercedes-Benz Parts Catalog Mercedes-Benz Accessories Catalog Mercedes-Benz Technical Articles Mercedes-Benz Tech Forums
 
Follow Pelican Parts on Facebook Follow Pelican Parts on Twitter Follow Pelican Parts on Instagram Follow Pelican Parts on YouTube Follow Pelican Parts on Pinterest Follow Pelican Parts on Tumblr
  Search our site:    
View Recent Cars  |   Cart  | Project List | Order Status | Help    
 >  >
Mercedes Brake Booster Diaphragm Positioning Sensor
 
Bookmark and Share

Pelican Technical Article:

Mercedes Brake Booster Diaphragm Positioning Sensor

Steve Vernon

Time:

3 hours3 hrs

Tab:

$220

Talent:

**

Tools:

13mm socket, T20 Torx, flare nut wrenches, power bleeder large

Applicable Models:

Mercedes-Benz W203 (2001-07)

Parts Required:

New sensor

Hot Tip:

Use paper towels and plastic bags to contain any fluid leaks

Performance Gain:

Better braking

Complementary Modification:

Replace brake booster

Without a doubt, your brakes are the most important systems on the car. Like most modern cars Mercedes boosts the braking system with a brake booster. There is a sensor that reads the position of the rubber diaphragm in the booster. If this sensor goes bad it can cause all kinds of problems with the boost and make for a mushy or too firm feel to the brake pedal

Replacing the brake booster diaphragm position sensors is not that difficult unfortunately you will need to remove the master cylinder to accomplish it as the sensor is tucked away below and behind the master cylinder. The first step is to disconnect the battery. Next remove the fluid level sensor connector from the top of the reservoir.

You'll want to try and get as much brake fluid as you can out of the fluid reservoir on top of the master cylinder. Open the cap on the reservoir and remove the strainer. Using a fluid pump or turkey baster, get as much of the old fluid out as you can. This helps prevent excessive spilling of brake fluid inside the engine compartment. It's also helpful to stuff a bunch of old rags or paper towels under the master cylinder to absorb any spills.

Use a 12mm flared nut wrench and remove the two brake lines from the master cylinder. Make sure you use a flared nut wrench and make sure that it is seated correctly; you do not want to strip the nut. Also be prepared to catch the small amount of brake fluid that is going to come out.

You are going to have to remove the brake lines that connect to the ABS unit to get the master cylinder out. Disconnect the lines from the ABS unit, follow the lines where they pass through the sheet metal and remove them from the rubber grommets and set them aside.

There is a rocker plenum on the front of the master cylinder. Remove the crush washer that secures it to the rubber grommet. The crush washer will need to be replaced as it is a single use piece. Slide the rocker off the front of the cylinder and remove it from the car.

Disconnect the brake pressure sensors from the bottom of each cylinder.

Now locate the two 13mm nuts on either side of the master cylinder. These nuts hold the master cylinder in place. You'll probably need an extension with a universal joint in order to reach both nuts. Pull the master cylinder straight forward off the brake booster then tilt it slightly sideways and remove it from the car. Note: When you reinstall the master cylinder the lower nut is very difficult to access. Try placing a small amount of tape or a small piece of rubber glove between the nut and socket to help keep the nut in place. Just make sure the threads are clear.

With the master cylinder removed you can see the sensor almost directly below the hole left by the master cylinder. Disconnect the wiring harness from the sensor by squeezing it and pulling straight back.

There is a metal circlip holding the sensor in place. Lift the metal clip with a flathead screw driver and pull the sensor out of the booster. There is a rubber gasket that helps seal the sensor to the booster, make sure you replace it and remove the old one before reinstalling.

Install the new sensors and reinstall the master cylinder. Now fill the master cylinder reservoir with new brake fluid and pump the pedal a few times to build up pressure. Do not pump the pedal without fluid in it. You could score and damage the inside of the cylinder bore, rendering it inoperable. You'll have to bleed all of the brake lines at each wheel to get all of the air out of the system. Please see our article on how to bleed your brakes.

DO NOT drive the car without completely bleeding the brakes

Next remove the level sensor (yellow arrow) connector from the top of the reservoir.
Figure 1

Next remove the level sensor (yellow arrow) connector from the top of the reservoir.

You'll want to try and get as much brake fluid as you can out of the fluid reservoir on top of the master cylinder.
Figure 2

You'll want to try and get as much brake fluid as you can out of the fluid reservoir on top of the master cylinder. Open the cap on the reservoir and remove the strainer. Using a fluid pump or turkey baster, get as much of the old fluid out as you can. This helps prevent excessive spilling of brake fluid inside the engine compartment. It's also helpful to stuff a bunch of old rags or paper towels under the master cylinder to absorb any spills.

Use a 12mm flared nut wrench and remove the two brake lines (red arrows) from the master cylinder.
Figure 3

Use a 12mm flared nut wrench and remove the two brake lines (red arrows) from the master cylinder. Make sure you use a flared nut wrench and that it is seated correctly, you do not want to strip the nut. Also be prepared to catch the small amount of brake fluid that is going to come out.

You are going to have to remove the brake lines that connect to the ABS unit to get the master cylinder out.
Figure 4

You are going to have to remove the brake lines that connect to the ABS unit to get the master cylinder out. Disconnect the lines (yellow and red arrows) from the ABS unit, follow the lines where they pass through the sheet metal and remove them from the rubber grommets (green arrow) and set them aside.

There is a rocker plenum on the front of the master cylinder.
Figure 5

There is a rocker plenum on the front of the master cylinder. Remove the crush washer (yellow arrow) that secures it to the rubber grommet. The crush washer will need to be replaced as it is a single use piece.

Slide the rocker off the front of the cylinder and remove it from the car.
Figure 6

Slide the rocker off the front of the cylinder and remove it from the car. Yellow arrow shows where the master cylinder sits and the red arrow shows how it attaches to the car.

Disconnect the brake pressure sensors wiring (yellow arrows) from the bottom of each cylinder.
Figure 7

Disconnect the brake pressure sensors wiring (yellow arrows) from the bottom of each cylinder.

Now locate the two 13mm nuts on either side of the master cylinder (yellow arrow, one shown).
Figure 8

Now locate the two 13mm nuts on either side of the master cylinder (yellow arrow, one shown). These nuts hold the master cylinder in place. You'll probably need an extension with a universal joint in order to reach both nuts.

Pull the master cylinder straight forward off the brake booster, then tilt it slightly sideways and remove it from the car.
Figure 9

Pull the master cylinder straight forward off the brake booster, then tilt it slightly sideways and remove it from the car. Make sure it clears the studs (red arrows) before tilting it to remove from the car.

With the master cylinder removed you can see the sensor almost directly below the hole left by the master cylinder.
Figure 10

With the master cylinder removed you can see the sensor almost directly below the hole left by the master cylinder. Disconnect the wiring harness (yellow arrow) from the sensor by squeezing it and pulling straight back.

There is a metal circlip holding the sensor in place.
Figure 11

There is a metal circlip holding the sensor in place. Lift the metal clip with a flathead screw driver (red arrow) and pull the sensor (yellow arrow) out of the booster.

There is a rubber gasket (yellow arrow) that helps seal the sensor to the booster, make sure you replace it and remove the old one before reinstalling.
Figure 12

There is a rubber gasket (yellow arrow) that helps seal the sensor to the booster, make sure you replace it and remove the old one before reinstalling.

13
Figure 13

When installing the master cylinder onto the brake booster take extreme care that the thrust rod sits into the master cylinder, other wise you can damage it and/or your brakes will not work!

Note: When you reinstall the master cylinder the lower nut is very difficult to access.
Figure 14

Note: When you reinstall the master cylinder the lower nut is very difficult to access. Try placing a small amount of tape or a small piece of rubber glove between the nut and socket to help keep the nut in place. Just make sure the threads are clear. Installation is the reverse of removal. DO NOT drive your car until you have completely bled your brakes!

Bookmark and Share
Comments and Suggestions:
omermurat Comments: Thank you very much for a very helpful tutorial.
My 2005 C230 had developed C1185 BAS diaphram travel sensor internal code and after a search I came across your site, red it and ordered the Brake booster Diaphragm Positioning Sensor. After replacing it, the brake pedal feels much firmer, however, the same C1185 is still there. Disconnected the battery for an hour and even reset the steering sensor but no help. Is there anything else I can do and/or check?
Thanks!
November 22, 2016
  Followup from the Pelican Staff: You may have to clear the fault code using a Mercedes-Benz scan tool. - Nick at Pelican Parts  
ma32asian Comments: thank-you
April 7, 2014
  Followup from the Pelican Staff: Thanks for the feedback. Glad we could help.
- Nick at Pelican Parts
 
Dickson Comments: The Brake booster Diaphragm Positioning Sensor is nothing to deal with the master cylinder. So, would it be possible to replace that sensor without removal the Master Cylinder? In your example, the reason to remove it simply because it gives way for sensor removal?
March 24, 2014
  Followup from the Pelican Staff: Yes, you should be able to replace it independently. - Nick at Pelican Parts  
F.A Comments: this is so very helpful thanks guys,but how do i solve this code c1100, I have BAS,ESP AND ABS DISPLAYING ON MY CLUSTER HOW DO I GO ABOUT IT.
April 10, 2013
  Followup from the Pelican Staff: You are welcome.

C1100 = Left Front Axle VSS Circuit Fault

The VSS = Vehicle Speed Sensor = Left front wheel speed sensor is dirty or damaged.
It must be cleaned and/or replaced to clear the code.
roy@pelicanparts.com -
 

  Search our site:    

View Cart & CheckOut | Project List | Order Status |  Help    

 

[Home] [Customer Service] [Shopping Cart] [Project/Wish List]
  [Privacy Statement]  [Contact Us] [About Us] [Shipping] [Careers]

Copyright © Pelican Parts Inc. -    DMCA Registered Agent Contact Page

Page last updated: Fri 12/9/2016 02:29:15 AM