Brakes
Brake Booster
The brake booster multiplies your pedal force using engine vacuum, so braking is effortless.
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Brake system flow
Interactive — tap a partTap a part to see how it fits in the system.
What it does
- Uses manifold vacuum to multiply pedal pressure
- Makes light pedal effort stop the car
- Fails open (hard pedal) rather than no brakes
When it fails
- Hard brake pedal with the engine running
- Hisssing noise when pressing the brake
- Spongy first part of the pedal
- Brakes work only with hard pressing
How to diagnose
- Pump the pedal with the engine off, hold, then start: the pedal should sink slightly
- Check the vacuum hose and check valve
- Listen for vacuum leaks
- Test the booster with a vacuum gauge
Maintenance
- Replace the vacuum hose when cracked
- Fix intake vacuum leaks that starve the booster
Use the diagnosis order. When a part fails, confirm each hypothesis with measurements before replacing anything — codes and symptoms overlap.
Related part
Master Cylinder
The master cylinder converts pedal force into hydraulic pressure for all four brakes.