Spongy or unusually soft brakes can indicate air in the hydraulic system, though other problems can cause similar symptoms. Because brakes are essential for vehicle control, the cause needs to be identified before the car is driven. Getting air out of brake lines—usually called bleeding the brakes—involves pushing old fluid and trapped air out through the wheel bleeder valves while keeping the master cylinder supplied with the correct fluid. The procedure varies by vehicle, especially when an anti-lock braking system (ABS) is involved, so the manufacturer’s service instructions take priority.
Brake work is a safety-critical repair. A professional technician is the safer choice if the vehicle-specific procedure is unavailable, a bleeder screw is seized, the reservoir has emptied, ABS service is required, or the pedal remains soft after bleeding. Professional help is also appropriate when the source of air is unclear, a warning light appears, or any leak or damaged component is found.
For general safety guidance, vehicle owners can consult their owner’s manual and the National Highway Traffic Safety Administration’s vehicle safety resources at NHTSA.gov. For the exact fluid, bleed order, and ABS procedure, the vehicle manufacturer’s service information is the controlling reference.