The power brake booster and vacuum brake booster are essentially the same part, utilizing vacuum pressure from the engine to assist braking. However, a hydro-boost power brake assist system works differently, using hydraulic pressure from the power steering pump rather than vacuum. Both vacuum and power brake boosters can fail if they lose vacuum pressure or have broken internal parts, while hydro-boost would fail at the same time as a power steering failure. Owners manuals can specify which type of brake booster a particular vehicle uses.