Mechanic Glossary

Vacuum Hose

A small rubber or silicone line that routes engine intake vacuum to control valves, sensors, and power brake boosters.

A vacuum hose is a piping line for engine vacuum. When an engine runs, the pistons draw air in, creating a suction vacuum behind the throttle plate. The engine uses this vacuum pressure to pull on diaphragms and operate valves. Vacuum hoses run from ports on the intake manifold to accessories like the brake booster, the EVAP canister purge valve, the fuel pressure regulator, and the climate control blend doors.

Rubber hoses get brittle over time due to engine heat. They dry out, crack, and split at the connection ports. This creates a "vacuum leak." Unregulated air enters the engine, making it idle rough, run lean, trigger misfires, or cause accessories like the brake booster to stop working, making the pedal hard to press.

Frequently Asked Questions

A high, rough, or erratic engine idle, a whistling or hissing sound under the hood, engine stalling, lean code check engine lights (P0171 or P0174), and a hard brake pedal.
You can use a smoke machine to pump smoke into the intake manifold with the engine off; smoke will exit from any crack in the hoses. Alternatively, spray soapy water or carburetor cleaner along the hoses while the engine is running and listen for a change in idle speed.
Yes. Silicone hoses withstand engine heat and ozone exposure much better than standard rubber, meaning they won't dry rot or crack over time. They are popular for performance builds.
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