Parts for your 2009 Subaru Impreza-Brake booster

2009 Subaru Impreza Brake Booster — What it does and when to service it

Technical documentation confirms the 2009 Subaru Impreza is fitted with a vacuum brake booster. The Subaru Impreza MY2009 Factory Service Manual (Brake section, Power Brake/Power Assist), Subaru’s FAST electronic parts catalogue listing “Booster Assy – Brake” for GE/GH/GR chassis, and the Haynes Repair Manual for Impreza 2008–2014 all describe the booster unit, its check valve and the diagnostic/adjustment procedures. So yes—this model uses a conventional vacuum-assisted brake booster.

On the 2009 Impreza, the brake booster’s job is to use engine vacuum to multiply pedal force, giving strong stopping power without needing to stand on the pedal. Mounted on the firewall behind the master cylinder, it smooths out braking feel, improves modulation in everyday traffic, and helps keep emergency stops predictable and straight. A one-way check valve in the vacuum line means there’s reserve assist even after the engine switches off or whilst the engine is under load.

There’s no set replacement interval for the booster—it's a fit-and-forget item—but it should be inspected during routine servicing. Techs usually check the vacuum hose condition, the one-way check valve operation, pedal free play and overall sealing. A quick driveway test is to pump the pedal a few times with the engine off, hold it, then start the engine: the pedal should drop slightly as vacuum assist kicks in.

• Common symptoms of trouble: a hard brake pedal, longer stopping distances, a constant hiss from the firewall, rough idle when braking, or brake fluid found inside the booster (often from a leaking master cylinder).
• Simple fixes first: replace cracked vacuum hoses or a faulty check valve. If the diaphragm inside the booster is torn or the unit won’t hold vacuum, the booster assembly needs replacing.

When replacing the booster on a 2009 Impreza, proper setup matters. The pushrod length between booster and master cylinder must be set to the factory spec from the service manual, get it wrong and pedal travel or draggy brakes will follow. Under the dash, the clevis-to-pedal pin and locknut should go back exactly where they were, with pedal free play checked to spec. After refitting, the braking system should be bled, a vacuum-function test performed, and a careful road test completed. For turbo variants, ensure the vacuum reservoir and lines are leak-free, as these cars rely more heavily on the check valve and reserve vacuum under boost. With the right checks, the Impreza’s brake pedal stays light, consistent, and confidence-inspiring across Kiwi and Aussie roads.

Popular questions about 2009 Subaru Impreza brake boosters

Does a 2009 Subaru Impreza definitely have a brake booster?
Yes. Factory literature (Subaru MY2009 Service Manual, Brake/Power Assist), the Subaru FAST parts catalogue, and mainstream repair manuals specify a vacuum brake booster on GE/GH/GR Impreza models, including WRX and non-turbo variants.

What are the signs the booster needs replacement, and can it be repaired?
Look for a rock-hard pedal, a hiss at the firewall, a dropping idle when braking, or evidence of brake fluid inside the booster. The hose and check valve are replaceable, the booster itself isn’t typically repairable—if the diaphragm or internal valve fails, the unit is replaced.

Is it safe to keep driving with a failing brake booster?
It will still stop, but pedal effort skyrockets and stopping distances blow out—especially at lower manifold vacuum. That’s not ideal for WoF/regos or daily safety. Best to have it inspected and sorted promptly.