Audi Workshop Service and Repair Manuals

Removing and installing hydraulic unit -N55- with ABS control unit -J104- Hydraulic unit -N55- with ABS control unit -J104- is located in the engine compartment (front left). Special tools and workshop equipment required

t  Brake pedal actuator -V.A.G 1869/2- t  Sealing plugs (repair kit) -1H0 698 311 A-   Caution ABS control unit -J104- and ABS hydraulic unit -N55- must not be separated. Removing –  Read out control unit version and note down. Use vehicle diagnosis and service information system -VAS 5051B- or -VAS 5052-. –  Disconnect battery → Rep. gr.27 (note radio code).

–  Insert brake pedal actuator -V.A.G 1869/2- between brake pedal and driver's seat (depress brake pedal at least 60 mm). This closes the valves in the brake master cylinder and stops the brake fluid reservoir from running dry. –  Connect hose of bleeder bottle to bleeder screw of front left brake caliper. –  Connect hose of bleeder bottle to bleeder screw of rear left brake caliper. –  Open bleeder screws of front left and rear left brake calipers to release pressure in hydraulic unit -N55-. –  Close bleeder screws (front left and rear left).   Note Do not remove brake pedal actuator -V.A.G 1869/2-.

–  Push retainer catch on electrical connector -1- for control unit upwards.

–  Pull retainer clip in -direction of arrow- and unplug connector.   Note t  Make sure brake fluid does not get into connector housing of control unit. This can result in corrosion of the contacts and failure of the system. t  Use compressed air to carefully clean connector housing if necessary. –  To protect against escaping brake fluid, place a sufficient number of lint-free cloths in area beneath control unit -J104- and hydraulic unit -N55-. –  Mark brake lines for subsequent installation.   WARNING Do not bend or kink brake lines. –  Disconnect brake lines between hydraulic unit -N55- and brake master cylinder.

–  Disconnect remaining brake lines -arrows- from hydraulic unit -N55-. –  Seal brake lines and threaded holes using sealing plugs from repair kit. –  Carefully lift hydraulic unit -N55- together with ABS control unit -J104- out of mounting bracket. Make sure that the rubber buffers do not drop into the engine compartment when detaching the ESP control assembly from the mounting bracket.   WARNING Severe shocks or jolts can damage the control unit. The control unit must not be re-installed if it has been damaged in any way. –  Place hydraulic unit -N55- on a clean flat surface with control unit -J104- facing downwards. Seal threaded holes and brake lines using sealing plugs after removing ABS control unit -J104- and hydraulic unit -N55-.   WARNING Hydraulic pump must not be separated from hydraulic unit -N55-. Installing Installation is performed in reverse sequence; note the following:   Note t  The hydraulic unit -N55- supplied as a replacement is filled with brake fluid. t  Do not remove sealing plugs from new hydraulic unit -N55- until corresponding brake line is ready to be fitted. t  If sealing plugs are removed from hydraulic unit -N55- before fitting corresponding brake line, brake fluid will escape. Proper bleeding is then no longer ensured. All rubber buffers must be fitted in the mounting bracket. –  Press hydraulic unit -N55- with control unit -J104- facing downwards into mounting bracket in vehicle. Hold the rubber buffers in place when pressing in the ESP control assembly to prevent them from dropping out. –  Connect brake lines as previously marked.   WARNING Interchanging brake line connections will result in ABS/ESP system malfunction.   Note Final control diagnosis can be used to establish whether line connections have been interchanged.

–  Connect all brake lines -arrows- to hydraulic unit -N55-.

Component		Nm
All brake lines to hydraulic unit		14

–  Attach electrical connector to control unit -J104-. –  Press down retaining clip so that it engages audibly.

–  Press down retainer catch -1- so it engages. –  Remove brake pedal actuator -V.A.G 1869/2-. –  Bleed brake system → Chapter. –  Perform final control diagnosis after securing brake lines to hydraulic unit -N55-.   Note Final control diagnosis can be used to establish whether line connections have been interchanged. Use vehicle diagnosis and service information system -VAS 5051B- or -VAS 5052- to do this. If a new ABS control unit -J104- has been fitted, it must be encoded. Use vehicle diagnosis and service information system -VAS 5051B- or -VAS 5052-. –  Select on the display: t  Running gear t  Brake system t  01 - Self-diagnosis compatible systems t  03 - Brake electronics. –  Select required function on the display: t  J104 Control unit for ABS/ASR/ESP t  J104 Control unit for ABS/ASR/ESP, functions t  J104 Code control unit Also calibrate the following senders after renewing control unit -J104-. t  Steering angle sender -G85- t  Lateral acceleration sender -G200- t  Longitudinal acceleration sender -G251- Use vehicle diagnosis and service information system -VAS 5051B- or -VAS 5052-. –  Select on the display: t  Running gear t  Brake system t  01 - Self-diagnosis compatible systems t  03 - Brake electronics. –  Select required function on the display: t  J104 Control unit for ABS/ASR/ESP t  J104 Control unit for ABS/ASR/ESP, functions. –  Then carry out ESP road test and system test.