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Audi A4 Brake Fluid Level Sensor Replacement
 
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Pelican Technical Article:

Audi A4 Brake Fluid Level Sensor Replacement

Steve Vernon

Time:

1 hour1 hr

Tab:

$40

Talent:

*

Tools:

Hands

Applicable Models:

Audi A4 (2002-05)
Audi A4 Cabriolet (2003-06)

Parts Required:

New brake fluid level sensor

Hot Tip:

Remove the brake booster vacuum hose

Performance Gain:

Proper brake booster function

Complementary Modification:

New brake fluid

Without a doubt, your brakes are the most important system on the car. Having a proper functioning brake system is the highest priority you should have on a running vehicle and that includes the fluid.

Brake fluid is hydroscopic, which means it absorbs water. Once the fluid has absorbed a certain percentage of moisture (usually around 2%) it must be changed. Water in the system can cause both corrosion to the brake system, as well as seriously degrade the performance or stopping power of your brakes.

Another important issue with the fluid is maintaining the proper level. If the brake fluid level gets too low, air can be introduced into the system and or you can lose brake pressure.

The Audi A4 has a built in brake fluid level sensor that can warn of an approaching dangerous low level of fluid. The nice thing about replacing the level sensor is it can be done quickly as well as without having to drain the reservoir. If you are changing out the sensor, it is also a good time to give the brake system a complete flush with new fluid. Follow the simple test listed below to determine if your sensor needs replacement.

To get access to the sensor you will need to first remove the battery cover and cowl (red arrow).
Figure 1

To get access to the sensor you will need to first remove the battery cover and cowl (red arrow). They both just pull off.

To test if your sensor is functioning correctly, clean around the filler cap and then remove it.
Figure 2

To test if your sensor is functioning correctly, clean around the filler cap and then remove it. With the ignition turned on, reach into the reservoir with a clean finger and press down on the strainer in the opening. Check that the warning light and alarm are set off in the dash. If neither warnings sound then the sensor is faulty.

The sensor is located directly below the small yellow tab on the reservoir (red arrow).
Figure 3

The sensor is located directly below the small yellow tab on the reservoir (red arrow). You will need to remove the vacuum line going into the brake booster to replace the sensor (yellow arrow). The vacuum line simply pulls out from the booster.

Note: I have removed the reservoir from the vehicle to photograph the procedures; you do NOT need to remove the reservoir to perform the work.
Figure 4

Note: I have removed the reservoir from the vehicle to photograph the procedures; you do NOT need to remove the reservoir to perform the work. Begin by unclipping the wiring connection to the sensor (red arrow).

There is a small plastic tab on the bottom of the sensor that sits in an opening on the channel in the reservoir.
Figure 5

There is a small plastic tab on the bottom of the sensor that sits in an opening on the channel in the reservoir. Push in the tab (red arrow) and pull the sensor straight back and out from the reservoir.

This photo illustrates the tab on the sensor that must be depressed to remove the sensor (red arrow).
Figure 6

This photo illustrates the tab on the sensor that must be depressed to remove the sensor (red arrow). Installation is the reverse of removal. If you have not given your brake fluid a flush in over a year or the vehicle is new to you, this would be a very good time to perform that work.



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