Mercedes of the S-class W202

1993-2000 of release

Repair and operation of the car

The serial ABS system prevents blocking of brakes at sharp braking. Thanks to it the car remains operated. The ABS system works at a speed more than 5 km/h and at the included ignition. It completely regulates braking process if car speed at least once exceeded 8 km/h.

The system measures the speed of rotation of wheels by means of two sensors on forward wheels and one sensor – on back. On signals of separate sensors the electronic device calculates the approximate average speed of the car. The operating device defines extent of pro-slipping of a separate wheel by comparison of speed of the car and establishes, brakes are how close to blocking.

As soon as the wheel showed tendency to blocking, the ABS system blocks pressure upon a brake, keeping the state given it. It means that pressure in the brake mechanism does not increase even in that case when pressing a pedal of a brake increases. If there is a tendency to blocking further, then pressure in this brake decreases the ABS system due to opening of the final valve. This process goes until the wheel does not start over again accelerating.

If the wheel starts over again accelerating, then ABS increases pressure in its brake system, but it does not reach value of pressure in the general brake system. This process repeats at sharp braking for each wheel so long, the brake pedal, respectively, to a full stop of the car will not be released (speed of 3 km/h) yet.

The security system in the electronic monitor watches that ABS was disconnected at faulty food or too low voltage (tension on the accumulator less than 11 V); in this case on the dashboard during a trip the control radiator of ABS lights up. The brake system at the same time functions as usual. The car when braking behaves as if the ABS system is absent.

The hydraulic device consists of the pump of the return giving, and also of three electromagnetic valves – on one for forward wheels, and one – for back brakes.

Increase in pressure: the inlet valve in the device of the electromagnetic valve is open, liquid pressure in the brake mechanism can increase to value which is provided with the main brake cylinder.

Pressure is constant: inlet and final valves in the device of the electromagnetic valve are closed. Liquid pressure in the brake mechanism does not change even if pressure between the main brake cylinder and the electromagnetic valve increases.

Pressure decline: the inlet valve in the electromagnetic valve is open. Brake fluid follows via the store from which it is pumped back in system of the main brake cylinder by the pump of the return giving.

It is required that liquid from the main brake cylinder was not lost. Operation of this pump is felt on noticeable pulsations of a brake pedal. Noise of the pump are weakened by means of a damper of a brake contour.

If during a trip the ABS indicator lights up, it specifies that the ABS system is disconnected.

Further inspections of ABS have to be carried out in a workshop. The operating device tests the ABS system before each trip and remembers the appeared malfunctions which codes remain in his memory even at shutdown of the accumulator. In company workshops these mistakes will be decoded by means of the special device, and then purposefully are eliminated.