Electronic Brake Control Module: Service and Repair
ABS Hydraulic Unit N55 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, 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 (N55) must not be separated.
Removing
- Read the 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.
- Insert the brake pedal actuator (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 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 bleeder screws on the left front and rear brake calipers to reduce the pressure in the ABS Hydraulic Unit (N55).
- Close left front and left rear bleeder screws.
• Do not remove brake pedal loading device (V.A.G 1869/2).
- Press securing clip on the connector to the control module - 1 - up.
- Pull securing bracket in direction of - 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 ABS Control Module (J104) and ABS Hydraulic Unit (N55).
- Mark brake lines for installation later.
Do not bend or kink the brake lines.
- Remove brake lines from the ABS Hydraulic Unit (N55) and brake master cylinder.
- Remove remaining brake lines - arrows - from the ABS Hydraulic Unit (N55).
- Seal brake lines and threaded holes with plugs from repair kit.
- Carefully remove the ABS Hydraulic Unit (N55) together with the ABS Control Module (J104) upward from the bracket.
When removing the ESP control module from the bracket, make sure the rubber buffers do not fall into the engine compartment.
Excessive shaking (e.g. dropping, impact) may destroy the control module. Control module must then no longer be used.
- Set the ABS Hydraulic Unit (N55) with the ABS Control Module (J104) down on a clean, level surface.
Seal the threaded holes and brake lines with plugs after removing the ABS Control Module (J104) and ABS Hydraulic Unit (N55).
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 ABS Hydraulic Unit (N55) is filled with brake fluid.
• Remove sealing plugs on the new ABS Hydraulic Unit (N55) when the corresponding brake line is going to be installed.
• If the sealing plugs are removed from the ABS 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 ABS Hydraulic Unit (N55) with the control module J104 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.
- Tighten all the brake lines - arrow - on the ABS Hydraulic Unit (N55).
- After securing the brake lines on the ABS Hydraulic Unit (N55), perform output diagnostic test mode.
• By performing the output check diagnosis, it can be determined if the connections were interchanged.
- Connect electrical connector on the ABS Control Module (J104).
- Press locking bracket down until it engages audibly.
- Press securing clip - 1 - down and engage it.
- Remove brake pedal loading device (V.A.G 1869/2).
- Bleed brake system. Refer to => [ Brake System, Bleeding ] Service and Repair.
Use the vehicle diagnosis, testing and information VAS 5051B or 5052 for this.
If ABS Control Module (J104) was replaced, it must be coded.
Use the vehicle diagnosis, testing and information system (VAS 5051B) or (VAS 5052) for this.
- On display, select:
• Chassis
• Brake System
• 01- On Board Diagnostic (OBD) capable systems
• 03 - 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 (J104).
• Steering Angle Sensor (G85)
• Transverse Acceleration Sensor (G200)
• Longitudinal Acceleration Sensor (G251)
Use the vehicle diagnosis, testing and information system (VAS 5051B) or (VAS 5052) for this.
- On display, select:
• Chassis
• Brake System
• 01- On Board Diagnostic (OBD) capable systems
• 03 - Brake electronics
- Select the following functions on the display:
• ABS/ASR/ESP control module J104
• ABS/ASR/ESP control module J104, functions.
- Then perform the ESP driving and system test.