Brake Master Cylinder

Replacement of the brake master cylinder on a 2024 Model S Long Range AWD. This is a hydraulic-only procedure that does not require HV system access, but the iBooster/electronic brake system will require bleeding and a scan-tool calibration after install.

Warnings

Tools required

Parts

• Brake master cylinder assembly (Model S 2024 specific) × 1 — OEM Tesla master cylinder for 2024 Model S — verify by VIN
• Master cylinder reservoir seal / O-rings (if supplied separately) × 1 — OEM seal kit as supplied with master cylinder
• Brake fluid (sealed, fresh) × 1 — DOT 3 — verify by VIN; some 2024 builds may specify DOT 4

Fluids

• DOT 3 Brake Fluid (verify spec on reservoir cap and by VIN) — 1 qt

Preparation

1. Park on level ground, place in P, and engage the parking brake.
2. Exit ALL doors with the key fob away from the vehicle. Wait at least 2 minutes for HV systems to fully de-energize, even on this non-HV job.
3. Open the frunk and disconnect the 12V low-voltage battery (located in the front trunk under the nose cowl panel on 2024 Model S). Isolate the negative terminal so it cannot accidentally re-contact.
4. DO NOT touch, cut, or pierce ANY orange cable — these are high-voltage and lethal.
5. If at any point you encounter an orange cable, an HV component, or are unsure if a system is de-energized: STOP and consult a Tesla-certified technician.
6. Place fender covers and absorbent material under and around the master cylinder area to protect aluminum panels and paint from brake fluid.
7. Verify the correct brake fluid specification stamped on the reservoir cap (DOT 3 or DOT 4) before opening any sealed fluid.
8. Confirm your scan tool can perform a Tesla brake system service bleed / iBooster calibration before disassembly — without it, the system cannot be returned to service.

Procedure

1. 1

   Access the master cylinder
   Remove the frunk liner and any cowl or trim panels required to expose the brake master cylinder, reservoir, and electronic booster assembly. Use plastic trim tools — do not pry against aluminum structure. Photograph all connector and line orientations before disturbing anything.
   ⚠Aluminum body — do not strike or wedge metal tools against panels.
2. 2

   Evacuate the brake fluid reservoir
   Using a clean, dedicated fluid evacuator or turkey baster, remove as much fluid as possible from the reservoir. Dispose of used fluid as hazardous waste. Do not allow fluid to drip onto body panels, wiring, or the HV pack venting under the vehicle.
   ⚠Brake fluid will strip aluminum-friendly paint instantly — keep absorbent material under all work areas.
3. 3

   Disconnect electrical connectors
   Disconnect the electronic brake booster harness connector(s) and the brake fluid level sensor connector at the reservoir. Move the harness aside and protect connector pins from fluid contamination.
4. 4

   Disconnect the hydraulic brake lines
   Using a proper flare-nut / line wrench, slowly loosen each hydraulic line at the master cylinder. Note the orientation and routing of each line. Cap each line and each master cylinder port immediately to prevent contamination and dripping. If a separate proportioning/pressure module is integrated, do not disturb its internal fittings.
   ⚠Use only a flare nut wrench — an open-end wrench will round the soft fitting hex.
   Torque spec

   Brake Line Fittings15 Nm (11 lb-ft)
5. 5

   Remove the master cylinder mounting nuts
   Support the master cylinder, then remove the nuts securing the master cylinder to the electronic booster / firewall mounting studs. Do not allow the unit to hang from any remaining line or harness.
   Torque spec

   Master Cylinder Nuts25 Nm (18 lb-ft)
6. 6

   Remove the master cylinder
   Carefully withdraw the master cylinder straight off its mounting studs to avoid bending or damaging the booster pushrod or seal. Place it port-up in a drip tray. Inspect the booster face and pushrod seal for fluid contamination — any fluid behind the seal indicates a booster issue that must be addressed before reassembly.
   ℹ️Fluid found behind the master cylinder indicates a leaking rear seal — the booster face must be inspected per the manufacturer-specified procedure.
7. 7

   Prepare the new master cylinder
   Transfer the reservoir to the new unit only if specified by the replacement part instructions, using new seals as supplied. Bench-bleed the new master cylinder per the manufacturer-specified procedure using the supplied bleed kit before installation. This is critical on electronic brake systems to prevent air ingestion into the booster module.
   ⚠Skipping bench bleeding can allow air into the iBooster-style module, which may require dealer-level service to recover.
8. 8

   Install the new master cylinder
   Align the new master cylinder onto the booster studs without cocking it. Hand-start both mounting nuts, then torque evenly in a cross pattern to the manufacturer-specified value. Verify the sequence with the Tesla Service Manual before final torque.
   ⚠Uneven tightening can crack the master cylinder flange or distort the booster seal.
   Torque spec

   Master Cylinder Nuts25 Nm (18 lb-ft)
9. 9

   Reconnect hydraulic lines
   Hand-thread each brake line fitting fully before applying any wrench torque to avoid cross-threading the soft alloy fittings. Torque each fitting using a flare nut / line wrench to the verified specification. Verify line routing matches pre-removal photos.
   Torque spec

   Brake Line Fittings15 Nm (11 lb-ft)
10. 10

    Reconnect electrical and fill reservoir
    Reconnect the booster harness and fluid level sensor. Fill the reservoir with fresh, sealed brake fluid matching the cap specification. Install the reservoir cap hand-tight only.
11. 11

    Bleed the brake system
    Connect a Tesla-compatible scan tool and initiate the manufacturer-specified electronic brake service bleed routine. Then bleed each caliper at the bleeder screw in the manufacturer-specified sequence using a pressure or vacuum bleeder until clean, bubble-free fluid emerges. Maintain reservoir level throughout — do not allow it to run dry. Torque each bleeder screw on completion.
    ⚠Without a scan tool the internal booster module will retain trapped air and the brake system will not function correctly.
12. 12

    Scan-tool calibration and clear codes
    Run the manufacturer-specified iBooster / brake module calibration routine. Clear any stored fault codes related to the brake system, ABS, stability control, or Autopilot. Confirm no active DTCs remain.

Reassembly

1. Reinstall any cowl panels, frunk liner, and trim removed for access.
2. Reconnect the 12V battery negative terminal and secure.
3. Close the frunk and verify the brake warning lamp on the dash extinguishes after wake-up.
4. Wipe down all aluminum surfaces in the work area with water and a clean cloth to neutralize any residual brake fluid.

Verification

• With the vehicle awake and brakes pumped firm, the pedal must feel solid with no spongy travel — pump and hold; pedal must not sink.
• Check for fluid weeping at all line fittings, the master cylinder flange, and each caliper bleeder under firm pedal pressure.
• On a closed, low-speed surface, perform a controlled brake test from ~10 mph and verify ABS, traction control, and stability control warnings are NOT illuminated.
• Verify regenerative braking and Autopilot/AEB readiness on the touchscreen — any disabled-feature alert indicates incomplete bleeding or calibration.
• Confirm reservoir level is at MAX cold and that the cap seals correctly.
• Record the service date — Tesla's published recommendation is brake fluid replacement every 2 years; this job resets that interval.

Related trouble codes on this vehicle

Codes that commonly send this job to the bay — tap one for symptoms, causes, and diagnostic steps.

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