my Volvo XC90's brakes feel spongy what could be wrong

Solution

1. Preparation

• Gather tools and parts required for the repair.
• Ensure the vehicle is on a flat surface and secure it with wheel chocks.
• Disconnect the battery to prevent electrical issues.

2. Inspect and Replace Brake Fluid

• Sub-steps:
  1. Remove the master cylinder reservoir cap.
  2. Inspect the brake fluid condition; if dark or contaminated, proceed to replace it.
  3. Using a turkey baster, siphon out old brake fluid from the reservoir.
  4. Fill the reservoir with new brake fluid (DOT 4 recommended for Volvo).
• Tools Required: Turkey baster, new brake fluid (DOT 4).
• Safety Warning: Brake fluid is corrosive; avoid contact with paint.

3. Bleed Brake Lines

• Sub-steps:
  1. Start with the brake furthest from the master cylinder (usually the passenger rear).
  2. Attach a brake bleeder kit to the brake bleeder valve on the caliper.
  3. Have an assistant pump the brake pedal while you open the bleeder valve to release air.
  4. Close the valve before your assistant releases the pedal.
  5. Repeat until no air bubbles are present in the fluid.
  6. Move to the next brake in this order: driver rear, passenger front, driver front.
• Tools Required: Brake bleeder kit, wrench for bleeder valves.

4. Inspect and Replace Brake Pads and Rotors (if necessary)

• Sub-steps:
  1. Remove the wheel.
  2. Inspect the brake pads for thickness; replace if less than 3mm.
  3. Check the rotors for scoring or excessive wear; replace if necessary.
  4. Install new brake pads and rotors, ensuring they are properly aligned.
  5. Reassemble the wheel and torque to manufacturer's specifications.
• Tools Required: Jack and jack stands, socket set, torque wrench.
• Safety Warning: Ensure the vehicle is securely supported before working underneath.

5. Test Brake Booster

• Sub-steps:
  1. Check the brake booster vacuum line for leaks or damage.
  2. With the engine off, press the brake pedal several times to deplete the vacuum.
  3. Start the engine and check if the brake pedal sinks slightly, indicating proper booster function.
• Tools Required: None specific.