Removing and installing hydraulic control unit (S6 and RS 6) — AUDI

🧭 Before you start

Disconnect the battery, remove the plenum chamber cover and depressurise the unit with the pedal held down and two bleed screws opened. Mark and disconnect the brake lines, plug everything, unplug the control unit connector and unbolt the unit. Fit the new unit, connect the lines as marked, lock the connector and tighten the unit after the lines. Bleed the brakes, code the control unit and run the final control diagnosis.

Fits: Audi A6 C6 (4F, 2004–2011)

• Opens: brake fluid
• Special tools named: VAS 5052

Don't miss

• Number every brake line before removal; the final control diagnosis reports interchanged connections.
• Keep brake fluid out of the control unit connector; blow it out carefully with compressed air if needed.
• Leave sealing plugs in the new unit until each line is ready, or it may not fill and bleed properly.
• Do not bend the brake lines near the hydraulic unit while pulling them out.
• Keep the pedal actuator in place until the new unit is fitted and the lines are tight.
• Code the ABS control unit and use the replace function in guided fault finding when renewing it.

Written for this job from the workshop steps below · TorqFix editorial.

📋 Procedure

1. ⚠ Do not bend the brake lines. — Note or request radio code on vehicles with coded radio if necessary.
2. Disconnect battery 27.
3. Detach plenum chamber cover 50.
4. To do so, remove rubber seal (1).
5. Insert brake pedal actuatorV.A.G 1869/2 between brake pedal and driver's seat. Depress the brake pedal at least 60 mm.

6. Connect hose of bleeder bottle to bleeder screws of front left and rear left brake calipers and open bleeder screws. [Note: This will release the pressure in the hydraulic unit.]
7. Close front left and rear left bleeder screws.
8. Do not remove brake pedal actuatorV.A.G 1869/2.
9. As protection against escaping brake fluid, place a sufficient number of lint-free cloths in area beneath control unit and hydraulic unit. [Note: Mark brake lines with numbers.]
10. ⚠ Do not bend the brake lines in the vicinity of the hydraulic unit. — Completely unscrew brake lines from brake master cylinder.
11. Disconnect remaining brake lines (arrows) on hydraulic unit.
12. Loosen bolts (1) at hydraulic control unit. [Note: To make it easier to pull out the rear left and rear right brake lines, loosen bolts (1) and press the hydraulic control unit slightly forwards towards the engine.]
13. Seal brake lines and tapped holes with sealing plugs from repair kit.
14. Press red retainer catch upwards. [Note: 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.Use compressed air to carefully clean connector housing if necessary.]
15. Release control unit connector (arrow) and unplug.
16. Push retaining clip in (direction of arrow) and unplug connector.
17. Remove bolts (1).
18. Remove hydraulic control unit. [Note: Do not remove sealing plugs from new hydraulic unit until corresponding brake line is ready to be fitted.If sealing plugs are removed from hydraulic unit sooner, brake fluid may escape and it may no longer be possible to fill and bleed the unit properly.]
19. Fit hydraulic control unit in bracket.
20. Connect pipes as previously marked: [Note: To make it easier to assemble the rear left and rear right brake lines, press the hydraulic control unit slightly forwards and tighten the bolts for the brake lines slightly.] [Note: Do not tighten bolts completely. This will make it easier to attach the individual brake lines to the hydraulic unit.]
21. Attach connector to hydraulic control unit and lock connector.
22. Press down red retainer catch (1).
23. After tightening brake lines, tighten hydraulic unit (1).
24. Remove brake pedal actuatorV.A.G 1869/2.
25. Bleed brake system .
26. Code ABS control unit with EDLJ104Coding control unit with VAS 5051B or VAS 5052 via function "Guided Fault Finding".
27. When renewing the control unit, select the "“Replace”" function for the relevant control unit in the "“Guided Fault Finding”".
28. Perform final control diagnosis after attaching brake lines to hydraulic unit. Vehicle diagnostic, testing and information systemVAS 5051B or VAS 5052 [Note: The final control diagnosis indicates whether the connection has been interchanged.]
29. Install plenum chamber cover 50.
30. Install rubber seal (1).

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