my BMW 3 Series has a spongy brake feel what could be the issue

Solution

1. Preparation

• Gather necessary tools and parts.
• Park the vehicle on a level surface and engage the parking brake.
• Safety: Ensure the vehicle is securely supported on jack stands if elevated.

2. Inspect and Top Off Brake Fluid

• Remove the master cylinder cap.
• Check brake fluid level; add the appropriate type of brake fluid (DOT 3 or DOT 4 as specified by the manufacturer) if low.
• Inspect the fluid for contamination (discoloration or particles). If contaminated, flush the system.

3. Inspect Brake Lines and Components

• Visually inspect all brake lines and hoses for leaks or damage.
• Check the brake calipers for any signs of leaking brake fluid.
• Tighten any loose connections.

4. Bleed the Brake System

• Start with the brake furthest from the master cylinder (usually the right rear).
• Use a brake bleeder kit or a helper to pump the brake pedal while you open the bleeder valve to release air.
• Repeat for each brake caliper in the correct sequence (typically right rear, left rear, right front, left front).
• Ensure the master cylinder does not run dry during the process.

5. Inspect Brake Components

• Remove the wheel to access brake pads, rotors, and calipers.
• Measure the thickness of brake pads; replace if below the manufacturer’s minimum specification.
• Inspect rotors for warping or scoring; replace if damaged.

6. Test the Brake Booster

• With the engine running, pump the brake pedal; it should feel firm. If the pedal sinks, the brake booster could be faulty.
• Inspect the vacuum line connected to the brake booster for leaks.