LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Audi >> 2009 >> A4 Avant Quattro >> Repair and Diagnosis >> Brakes >> Traction Control >> Anti-Lock Brake System (AVANT) >> Anti-Lock Brake System >> Removal And Installation >> Abs Hydraulic Unit With Abs Control Module
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Abs Hydraulic Unit With Abs Control Module

The ABS hydraulic unit N55 with ABS control module J104 is located in the left front of the engine compartment.

Special tools and workshop equipment required 

CAUTION:

The ABS control module J104 and ABS hydraulic unit N55 must not be separated.

Removing 

-- Read control module version and make a note of it.

Use vehicle diagnosis, testing and information system VAS 5051B or VAS 5052 for this.

-- Disconnect battery, refer to Removal and Installation , note radio code.

-- Insert brake pedal actuator V.A.G 1869/2 between brake pedal and driver seat by pressing brake pedal down at least 60 mm. By doing this, the valves in the brake master cylinder are closed and the brake fluid reservoir does not run empty.

Fig 1: Brake Pedal Depressor VAG 1869/2 Inserted Between Brake Pedal And Driver's Seat
GWWA44-0020Courtesy of AUDI OF AMERICA, LLC

-- Connect hose from a bleeder bottle to bleeder screw on left front caliper.

-- Connect hose from a bleeder bottle to bleeder screw on left rear caliper.

-- Open bleeder screws on left front and rear brake calipers to reduce pressure in the ABS hydraulic unit N55.

-- Close left front and left rear bleeder screws.

NOTE:

Do not remove brake pedal loading device V.A.G 1869/2.

-- Press securing clip on connector to the control module -1- up.

Fig 2: Identifying Brake Lines
GWWA45-10016Courtesy of AUDI OF AMERICA, LLC

-- Pull securing bracket in direction of -arrow- and remove connector.

Fig 3: Pushing Retaining Plate And Disconnecting Connector
GWWA45-10017Courtesy of AUDI OF AMERICA, LLC
NOTE:
  • Ensure no brake fluid enters control module connector housing. This could lead to corrosion of the contacts and thereby cause the system to fail.
  • A contaminated connector housing must be carefully cleaned with compressed air.

-- To protect against escaping brake fluid, place a lint-free cloth in the area under the control module J104 and hydraulic unit N55.

-- Mark brake lines for installation later.

WARNING:

Do not bend or kink the brake lines.

-- Remove brake lines from ABS hydraulic unit N55 and brake master cylinder.

-- Remove remaining brake lines -arrows- from ABS hydraulic unit N55.

Fig 4: Identifying Brake Lines
GWWA45-10016Courtesy of AUDI OF AMERICA, LLC

-- Seal brake lines and threaded holes with plugs from repair kit.

-- Carefully remove ABS hydraulic unit N55 together with ABS control module J104 upward from bracket.

NOTE:

When removing the ESP control module from the bracket, make sure the rubber buffers do not fall into the engine compartment.

WARNING:

Excessive shaking (e.g. dropping, impact) may destroy the control module. Control module must then no longer be used.

-- Set hydraulic unit N55 with control module J104 down on a clean, level surface.

NOTE:

Seal threaded holes and brake lines with plugs after removing the ABS control module J104 and ABS hydraulic unit N55.

WARNING:

The hydraulic pump must not be separated from the hydraulic unit N55.

Installing 

Installation is in reverse order of removal, with special attention to the following:

NOTE:
  • For customer service, the hydraulic unit N55 is filled with brake fluid.
  • Remove sealing plugs on the new hydraulic unit N55 when the corresponding brake line is going to be installed.
  • If the sealing plugs are removed from the hydraulic unit N55 before installing the corresponding brake line, the brake fluid will drain. If that is the case, sufficient brake system bleeding can no longer be ensured.
NOTE:

All the rubber buffers must be inserted in the bracket.

-- Press hydraulic unit N55 with control module J104 down into bracket in the vehicle.

NOTE:

When pressing ESP control module into the bracket, counterhold the rubber buffers so they do not fall through.

-- Connect brake lines according to the markings.

CAUTION:

If the brake line connectors are replaced, an ABS/ESP system malfunction will register.

NOTE:

By performing the output check diagnosis, it can be determined if the line connections were interchanged.

-- Tighten all brake lines -arrow- on hydraulic unit N55.

Fig 5: Identifying Brake Lines
GWWA45-10016Courtesy of AUDI OF AMERICA, LLC
Component   Nm
All brake lines to the hydraulic unit 14

-- Connect electrical connector on control module J104.

-- Press locking bracket down until it engages audibly.

-- Press securing clip -1- down and engage it.

Fig 6: Identifying Brake Lines
GWWA45-10016Courtesy of AUDI OF AMERICA, LLC

-- Remove brake pedal loading device V.A.G 1869/2.

-- Bleed brake system BRAKE SYSTEM, BLEEDING .

-- After securing brake lines on hydraulic unit N55, perform output diagnostic test mode.

NOTE:

By performing the output check diagnosis, it can be determined if the line connections were interchanged.

Use vehicle diagnosis, testing and information VAS 5051B or 5052 for this.

If ABS Hydraulic Unit J104 was replaced, it must be coded.

Use vehicle diagnosis, testing and information system VAS 5051B or VAS 5052 for this.

-- On display, select:

-- Select the following functions on the display:

The following sensors should also be calibrated after replacing control module J104.

Use vehicle diagnosis, testing and information system VAS 5051B or VAS 5052 for this.

-- On display, select:

-- Select the following functions on the display:

-- Then perform the ESP driving and system test.

scientia non olet · About LEMON Manuals