Removing and installing ABS control unit J104/ABS hydraulic unit N55, RHD vehicles — VW
Removing and installing ABS control unit J104/ABS hydraulic unit N55, RHD vehicles on VW: 25 steps. What to remove, in what order, and what to check after.
Removing the ABS control unit J104 with hydraulic unit N55 on right-hand-drive versions of the platform code listed below means working down the side of the engine bay with the air filter housing, battery and tray out of the way. Before anything is unbolted, read and note the existing control unit coding. The brake pedal is held down at least 60 mm with V.A.G 1869/2 while the left-hand bleed valves are opened, which stops the reservoir emptying when the lines come off. The master cylinder lines are identified and released first, then the four caliper lines, each sealed immediately with plugs from repair kit 1H0 698 311 A. Careful line identification, not bending the pipes at the unit, and keeping the new unit plugged until each line is fitted decide whether the brakes bleed up properly afterwards.
🧭 Before you start
Note the control unit coding, remove air filter housing, battery and tray, and hold the pedal down with V.A.G 1869/2 after opening the front and rear left bleed valves. Identify and remove the two master cylinder lines and the four caliper lines, sealing each at once, then unplug the connector, remove the retainer bolt and pull the unit out of its rubber dampers. Separate the control unit, spray the dampers with silicone lubricant on refit, check seating, bleed the brakes and code J104.
Fits: platform code 138
- Opens: brake fluid
Don't miss
- Read and note the existing coding before disconnecting the control unit.
- Do not bend brake lines at the hydraulic unit; mark each line before unscrewing.
- Unplug the new unit's ports one at a time, only as each line is fitted.
- Spray the rubber dampers with silicone lubricant and make sure they stay in the bracket.
- Bleed the brake system and code J104 before the car leaves.
Written for this job from the workshop steps below · TorqFix editorial.
📋 Procedure
- ⚠ Do not bend the brake lines in the area of the hydraulic unit! — Read out and note the existing control unit code.
- Removing air filter housing:
- Remove battery Electrical system27Battery; Removing and installing battery.
- Remove battery tray (arrows).
- Apply brake pedal depressorV.A.G 1869/2.
- Connect hose of bleed bottle (1) to bleed valve of front left brake caliper.
- Open bleed valve.
- Connect hose of bleed bottle (1) to bleed valve of rear left brake caliper.
- Open bleed valve.
- Depress brake pedal at least 60 mm using brake pedal actuatorV.A.G 1869/2.
- Close front left and rear left bleeder valves.
- Do not remove brake pedal depressorV.A.G 1869/2.
- Place sufficient lint-free cloths under the control unit and hydraulic unit.
- First identify the two brake master cylinder brake lines (A) and (B) and unscrew from the hydraulic unit.
- Immediately seal brake lines and threaded holes using sealing plugs from repair kit1H0 698 311 A.
- Identify brake lines (brake calipers) (1 to 4), unscrew and seal.
- Release connector in direction of (arrow 1).
- Disconnect connector in direction of (arrow 2).
- Unscrew bolt (3) from retainer.
- Pull hydraulic unit together with control unit and retainer sideways out of rubber dampers of bracket.
- Unbolt control unit from hydraulic unit [Note: Remove sealing plugs from new hydraulic unit only when the corresponding brake line is to be fitted.If sealing plugs are removed too early from the hydraulic unit, brake fluid can escape, and it can then no longer be guaranteed that the unit can be sufficiently filled and bled.]
- Before installing bracket of ABS hydraulic unit N55 into console, spray rubber dampers with silicone lubricantD 007 000 A2.
- ⚠ Ensure that rubber dampers of retainer are not pressed out of bracket when installing. After installing, check hydraulic unit with control unit for proper seating, otherwise malfunctions can occur. — Remove brake pedal depressorV.A.G 1869/2.
- Bleed brake system .
- Coding ABS control unit J104: .
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Who makes these pages, and how
TorqFix was built by a mechanic — after a 2,700 km drive with five roadside repairs that no diagnostic tool could explain.
The figures on this page come from manufacturer workshop documentation and are shown as they are. The page is assembled automatically from that data — it is not written by an AI. The AI works in the chat, where it answers for your specific car. It writes nothing here.
Variants of the same model differ. Cross-check torque against the factory manual for your engine before final tightening.
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The story behind TorqFix →Workshop data on this page last updated 20 Sep 2026.