Brake Booster

Replace the electric brake booster assembly on a 2023 Rivian EDV 500, including disconnecting the high-voltage system, removing the master cylinder, and installing a new brake booster unit.

Warnings

Tools required

Parts

• Electric brake booster assembly × 1 — Use OEM Rivian specification
• Brake booster mounting gasket/seal × 1 — Use OEM specification
• Brake line copper crush washers × 4 — Use OEM specification

Fluids

• DOT 4 Brake Fluid — 1 qt

Preparation

1. Park vehicle on level surface and engage parking brake
2. Chock rear wheels securely
3. Ensure 12V battery is fully charged (critical for maintaining vehicle systems during repair)
4. Put on high-voltage safety gloves and ensure insulated tools are available
5. Access the Rivian service mode through the center display: Settings > Service > Service Mode
6. Place 'HIGH VOLTAGE WORK IN PROGRESS' warning tags on steering wheel and charge port
7. Open hood and locate the high-voltage disconnect (under front trunk liner, driver side)
8. Remove HV service disconnect plug and store in your pocket (never leave accessible to others)
9. Wait minimum 5 minutes for high-voltage capacitor discharge
10. Verify zero voltage across HV terminals using insulated multimeter rated for DC voltage measurement
11. Disconnect 12V negative battery terminal
12. Remove front trunk liner panels to access master cylinder and brake booster area
13. Place absorbent pads and brake fluid catch container under master cylinder area

Procedure

1. 1

   Remove brake fluid from reservoir
   Using a turkey baster or brake fluid syringe, remove as much brake fluid as possible from the master cylinder reservoir. This minimizes spillage during brake line disconnection. Dispose of old fluid properly; do not reuse.
   ⚠Brake fluid damages paint immediately. Cover surrounding areas with protective material.
2. 2

   Disconnect brake lines from master cylinder
   Using flare nut wrenches, carefully loosen and disconnect all four brake lines from the master cylinder. Work slowly to avoid rounding the fittings. Cap or plug the brake lines immediately with clean rubber caps to prevent contamination and further fluid loss. Note the position of each line for reassembly.
   ⚠Use only flare nut wrenches to prevent rounding brake line fittings. Standard wrenches will likely damage the soft brass fittings.
3. 3

   Disconnect brake booster electrical connectors
   Locate the main electrical connector on the electric brake booster (typically a large multi-pin connector on the booster body). Press the locking tab and carefully disconnect. Also disconnect the brake fluid level sensor connector at the master cylinder reservoir. Verify no other electrical connections remain.
   ℹ️Take photos of connector positions and routing before disconnection to aid reassembly.
4. 4

   Access brake pedal pushrod connection
   From inside the vehicle, remove the lower driver's side dashboard panel to access the brake pedal assembly. Locate where the brake booster pushrod connects to the brake pedal arm. This typically uses a clevis pin with a retaining clip.
   ⚠The brake pedal spring is under tension. Control the pedal when disconnecting to prevent sudden movement.
5. 5

   Disconnect pushrod from brake pedal
   Remove the retaining clip or cotter pin securing the clevis pin that connects the pushrod to the brake pedal. Remove the clevis pin and disconnect the pushrod from the pedal. The brake pedal will now move freely.
6. 6

   Remove brake booster mounting nuts
   Return to the engine compartment. Locate the four mounting nuts securing the brake booster to the firewall (typically 13mm or 14mm). Remove all four nuts while supporting the brake booster and master cylinder assembly. Note the position of any spacers or washers.
   ⚠The brake booster and master cylinder assembly is heavy (approximately 20-25 lbs). Have an assistant help support it or use a suitable stand.
7. 7

   Remove brake booster assembly
   Carefully pull the brake booster and master cylinder assembly forward and away from the firewall. Maneuver it out of the engine compartment, being careful not to damage surrounding components or spill remaining brake fluid. Place on a clean work surface.
8. 8

   Inspect firewall mounting surface and seal
   Inspect the firewall mounting surface for damage, corrosion, or distortion. Clean the mounting surface thoroughly. Inspect the rubber seal/gasket on the firewall where the booster mounts. Replace if damaged or deteriorated.
9. 9

   Prepare new brake booster assembly
   Unpack the new electric brake booster assembly. Verify it matches the original unit exactly (connector position, mounting pattern, pushrod length). Install a new mounting gasket/seal if provided. Check that the pushrod adjustment is correct (should match original unless otherwise specified by Rivian service documentation).
   ⚠Incorrect pushrod length will cause brake pedal height issues and potential brake system malfunction. Verify against OEM specifications.
10. 10

    Install new brake booster to firewall
    Position the new brake booster assembly against the firewall, ensuring the pushrod passes through the firewall opening into the passenger compartment. Align the mounting studs with the firewall holes. Install the four mounting nuts and tighten in a cross-pattern to ensure even seating. Tighten securely but do not overtighten (typically 15-20 ft-lbs, verify with Rivian service documentation if available).
11. 11

    Reconnect pushrod to brake pedal
    From inside the vehicle, align the brake booster pushrod clevis with the brake pedal arm. Install the clevis pin and secure with a new retaining clip or cotter pin. Verify the connection is secure and the pedal moves smoothly through its full range without binding.
12. 12

    Reconnect brake lines to master cylinder
    Remove the protective caps from the brake lines. Install new copper crush washers on each brake line fitting. Thread each brake line into the correct master cylinder port by hand first to prevent cross-threading. Once hand-tight, use flare nut wrenches to tighten securely (typically 10-12 ft-lbs). Double-check each connection is tight.
    ⚠️Ensure brake lines are connected to the correct ports. Incorrect routing can cause brake system malfunction and potential loss of braking on one or more wheels.
13. 13

    Reconnect electrical connectors
    Reconnect the main electrical connector to the brake booster, ensuring it clicks into place securely. Reconnect the brake fluid level sensor connector. Verify all connections are fully seated and latched.
14. 14

    Fill and bleed brake system
    Fill the master cylinder reservoir with fresh DOT 4 brake fluid to the MAX line. Using a vacuum brake bleeder or pressure bleeder, bleed all four wheels in the proper sequence (typically RR, LR, RF, LF for this vehicle, but verify with Rivian service documentation). Continue bleeding until all air is removed and only clean, bubble-free fluid emerges. Maintain reservoir level throughout bleeding process.
    ⚠️Air in the brake system will cause brake failure. Ensure complete bleeding of all lines. Pump brake pedal multiple times and verify firm pedal feel before attempting to drive.
15. 15

    Reconnect 12V battery and restore high-voltage system
    Reconnect the 12V negative battery terminal. Reinstall the high-voltage service disconnect plug. Remove lockout/tagout warnings. Power on the vehicle and verify no error messages on the instrument cluster related to the brake system.
16. 16

    Perform brake system initialization and ADAS calibration
    Using the Rivian diagnostic scanner, perform the brake system initialization procedure. This allows the electronic brake booster control module to calibrate sensors and perform self-tests. Also perform ADAS recalibration if required (the brake system interfaces with stability control and driver assistance systems). Follow all on-screen prompts and complete all initialization sequences.
    ⚠️Vehicle is NOT safe to drive until brake system initialization and ADAS calibration are successfully completed. The brake booster will not function properly without this step.

Reassembly

1. Reinstall all dashboard panels and front trunk liner panels removed during disassembly
2. Verify all electrical connectors are secure and properly routed
3. Check master cylinder reservoir fluid level and top off to MAX line with fresh DOT 4 fluid
4. Verify no brake fluid leaks at any connection points
5. Remove all tools and materials from vehicle and engine compartment

Verification

• With vehicle stationary, pump brake pedal 10-15 times and verify firm, consistent pedal feel with no gradual pedal sink
• Start vehicle and verify brake booster electrical operation (may hear a brief motor sound at startup)
• Check instrument cluster for any brake system warning lights or fault codes
• Verify brake pedal height is correct and consistent with pre-repair measurement
• Perform parking lot low-speed brake test (under 10 mph) to verify basic braking function before road test
• Perform controlled road test in a safe area, testing brakes at progressively higher speeds up to normal operating speed
• Test ABS function if possible in a safe, controlled environment (wet surface or gravel at low speed)
• Verify stability control and traction control systems function normally
• Re-check all brake line connections for leaks after road test
• Re-check master cylinder fluid level after road test and top off if needed
• Clear all service mode settings and return vehicle to normal operation
• Document all work performed, including initialization and calibration completion

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