The vehicle might have the Antilock Brake System (ABS), an advanced electronic braking system that helps prevent a braking skid.
If the vehicle has ABS,
this warning light on the
instrument panel comes
on briefly when the
vehicle is started.
When the engine is started, or when the vehicle begins to drive away, ABS checks itself. A momentary motor or clicking noise might be heard while this test is going on, and it might even be noticed that the brake pedal moves or pulses a little. This is normal.
Let us say the road is wet and you are driving safely.
Suddenly, an animal jumps out in front of you. You slam
on the brakes and continue braking. Here is what
happens with ABS:
A computer senses that the wheels are slowing down.
If one of the wheels is about to stop rolling, the computer will separately work the brakes at each wheel.
ABS can change the brake pressure to each wheel, as required, faster than any driver could. This can help the driver steer around the obstacle while braking hard.
As the brakes are applied, the computer keeps receiving updates on wheel speed and controls braking pressure accordingly.
Remember: ABS does not change the time needed to get a foot up to the brake pedal or always decrease stopping distance. If you get too close to the vehicle in front of you, there will not be enough time to apply the brakes if that vehicle suddenly slows or stops. Always leave enough room up ahead to stop, even with ABS.
Chevrolet Cobalt Service & Repair Manual. General Service
Two basic types of power assist
mechanisms are used: vacuum assist diaphragm assemblies, which use engine
vacuum or in some cases vacuum pressure developed by an external vacuum
pump. The second type is a hydraulic pressure assist mechanism, which use
pressure developed by an ...