Electronic Brake Control Module: Service and Repair
ABS Hydraulic Unit (N55) with ABS Control Module (J104)
The ABS hydraulic unit N55 with ABS control module J104 is located in the left front of the engine compartment.
Special tools, testers and auxiliary items required
• Brake Pedal Actuator (V.A.G 1869/2)
• Repair Kit Plugs (1H0 698 311 A)
The ABS control module J104 and ABS hydraulic unit must not be separated.
Removing
- Read the control module version and make a note of it.
• Use the vehicle diagnostic tester (VAS 5051B) or (VAS 5052) for this.
- Disconnect the battery, noting the radio code.
- Insert the (V.A.G 1869/2) between the brake pedal and driver seat by pressing the 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.
- Connect the hose from a bleeder bottle to the bleeder screw on the left front caliper.
- Connect the hose from a bleeder bottle to the bleeder screw on the left front caliper.
- Open the bleeder screws on the left front and rear brake calipers to reduce the pressure in the ABS hydraulic unit.
- Close the left front and left rear bleeder screws.
• Do not remove (V.A.G 1869/2).
- Press the securing clip on the connector to the control module - 1 - up.
- Pull the securing bracket in the - direction of the arrow - and remove the connector.
• Make sure that 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.
- Mark the brake lines for installation later.
Do not bend or kink the brake lines.
- Remove the brake lines from the ABS hydraulic unit and brake master cylinder.
- Remove the remaining brake lines - arrows - from the ABS hydraulic unit.
- Seal brake lines and threaded holes with plugs from repair kit.
- Carefully remove the ABS hydraulic unit together with the ABS control module upward from the bracket.
• When removing the ESP control unit from the bracket, make sure the rubber buffers do not fall into the engine compartment.
Excessive shaking (for example dropping, impact) may destroy the control module. Control module must then no longer be used.
- Set the ABS hydraulic unit with ABS control module down on a clean, level surface.
• Seal the threaded holes and brake lines with plugs after removing the ABS control module and ABS hydraulic unit.
The hydraulic pump must not be separated from the hydraulic unit N55.
Installing
Installation is the reverse of removal, with special attention to the following:
• For customer service, the hydraulic unit N55 is filled with brake fluid.
• Remove the 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.
• All the rubber buffers must be inserted in the bracket.
- Press the hydraulic unit with the ABS control module down into the bracket in the vehicle.
• When pressing the ESP control unit into the bracket, counterhold the rubber buffers so they do not fall through.
- Connect the brake lines according to the markings.
If the brake line connectors are replaced, an ABS/ESP system malfunction will register.
• By performing the output check diagnosis, it can be determined if the line connections were interchanged.
- Tighten all the brake lines - arrow - on the ABS hydraulic unit.
- Connect the electrical connector on the ABS control module.
- Press the locking bracket down until it engages audibly.
- Press the securing clip - 1 - down and engage it.
- Remove the (V.A.G 1869/2).
- Bleed the brake system, refer to => [ Brake System, Bleeding ] Service and Repair.
- After securing the brake lines on the hydraulic unit, perform output diagnostic test mode.
• By performing the output check diagnosis, it can be determined if the line connections were interchanged.
Use the vehicle diagnostic tester (VAS 5051B) or (5052) for this.
If ABS hydraulic unit was replaced, it must be coded.
Use the vehicle diagnostic tester (VAS 5051B) or (5052) for this.
- On display, select:
• Chassis
• Brake System
• 001 - OBD-capable systems
• 003- Brake electronics.
- Select the following functions on the display:
• ABS/ASR/ESP control module J104
• ABS/ASR/ESP control module J104, functions
• J104 Coding control module
The Following Sensors Should Also be Calibrated After Replacing ABS control module.
• Steering Angle Sensor (G85)
• Transverse Acceleration Sensor (G200)
• Longitudinal Acceleration Sensor (G251)
Use the vehicle diagnostic tester (VAS 5051B) or (5052) for this.
- On display, select:
• Chassis
• Brake System
• 001 - OBD-capable systems
• 003- Brake electronics.
- Select the following functions on the display:
• ABS/ASR/ESP control module.
• ABS/ASR/ESP control module functions.
- Then perform the ESP driving and system test.