TTEC 4825 ABS On-Car "Range Rover".

                     
                                                     ABS System.

                                                    Range Rover

                                                   Identification

                               Brake Master Cylinder and Brake Booster

The master cylinder displaces hydraulic pressure to the rest of the brake system. It holds THE most important fluid in your car, the brake fluid. It actually controls two seperate subsystems which are jointly activated by the brake pedal. This is done so that in case a major leak occurs in one system, the other will still function. The two systems may be supplied by seperate fluid reservoirs, or they may be supplied by a common reservoir.
Electronic sensors within the master cylinder are used to monitor the level of the fluid in the reservoirs, and to alert the driver if a pressure imbalance develops between the two systems. If the brake light comes on, the fluid level in the reservoir(s) should be checked. If the level is low, more fluid should be added, and the leak should be found and repaired as soon as possible. 

In a vacuum booster type system, pressure on the brake pedal pushes forward a pushrod connected to the pistons within the master cylinder. At the same time, the pushrod opens the vacuum-control valve so that it closes the vacuum port and seals off the forward half of the booster unit. The engine vacuum line then creates a low-pressure vacuum chamber. Atmospheric pressure in the control chamber then pushes against the diaphragm. The pressure on the diaphragm forces it forward, supplying pressure on the master cylinder pistons.

                            ABS: Control Unit, Modulator, Pump Motor

Controller
The controller is a computer in the car. It watches the speed sensors and controls the valves.

Pump

Since the valve is able to release pressure from the brakes, there has to be some way to put that pressure back. That is what the pump does; when a valve reduces the pressure in a line, the pump is there to get the pressure back up.

Valves
There is a valve in the brake line of each brake controlled by the ABS.

Brake Fluid

Brake fluid is a special liquid for use in hydraulic brake systems, which must meet

highly exact performance specifications. It is designed to be impervious to wide

temperature changes and to not suffer any significant changes in important physical

characteristics such as compressibility over the operating temperature range.

The fluid is designed to not boil, even when exposed to the extreme temperatures

of the brakes.

                                        Fuse Box with ABS fuse F51

                                      Inductive Speed sensor

                                            Hall-Effect speed Sensor

Wheel Speed Sensors measure the road-wheel speed and direction of rotation. These sensors provide input to a number of different automotive systems including the anti-lock brake system and electronic stability control. Wheel speed sensors typically include a toothed (or optically encoded) shaft and a magnetic (or optical) sensor. The sensor counts the rate at which the teeth or marks pass by. Wheel speed sensors may monitor the crankshaft or driveshaft rotation in vehicles that do not need to know the rate at which individual wheels are turning. Otherwise, they monitor the rotation of the axle driving each wheel.

Brake Warning System

connected to the master cylinder. It monitors differences in pressure in the brake lines of the two hydraulic sub-systems, and alerts the driver with a light if an imbalance occurs. When you turn the key to the Ignition position, the brake warning light on the dash comes on during a "self-test". You should not drive a car if the warning light does not come on during the startup self test
The brake system is divided into two sub-systems to increase safety. A pressure differential switch, connected to the warning light, is positioned between the two. If a major leak occurs, and therefore pressure in one of the lines is sharply reduced, pressure from the other side forces a piston to move, activating the pressure differential switch and turns on the dashboard warning light.
  The brake warning light is also connected to the brake fluid level sensors in the master cylinder reservoir(s). If the brake warning light comes on, the fluid level should be checked. If the level is low, more fluid should be added, and the leak should be found and repaired as soon as possible.

Anti-lock Brake Systems (ABS)

Originally developed for aircraft, ABS basically works by limiting the pressure to any wheel which decelerates too rapidly. This allows maximum stopping force to be applied without brake lockup (skidding). If standard brakes are applied too hard, the wheels "lock" or skid, which prevents them from giving directional control. If directional control (steering) is lost, the vehicle skids in a straight line wherever it is going. ABS allows the driver to steer during hard braking, which allows you to control the car much better. In the old days, drivers had to know how to "pump" the brakes or sense the lockup and release foot pressure in order to prevent skidding. This meant that if only one wheel lost traction and started to skid, the driver would have to reduce braking force to prevent a skid. The advantage of ABS is that the brakes on the wheels with good traction can be used to the fullest possible amount, even if other wheels lose traction.