Anti-lock braking system (ABS

Self Repair ABS does not recommend, except for removing and installing the speed sensor. Ahead of the sensors installed in the steering knuckle, rear - semi-axes in the rear suspension.

When working on vehicles with ABS should observe the following precautions:

- During welding must be removed from the connector of the electronic control unit;

- If the car does not stain on the name Mercedes SRT, should notify that the apparatus can be only for a short time at a temperature of 95 ?� C and not more than two hours at 85 ?� C;

- When connected firmly tighten the battery terminals.

When working on the brake system should be checked the serviceability of the ABS as follows:

- Start up the engine and check that the yellow lamp in the instrument cluster with the designation ABS extinguished and the speed of 5-7 km / h do not light up;

- The system starts from the moment when the achieved rate of 5-7 km / h. All brake applications are regulated from the occurrence of the so-called field block with a speed of 8 km / h.

The system operates as follows. As the wheel speed, measured by the sensor, defined deceleration and acceleration signals which are transmitted to the electronic control unit. The signals from the individual wheels forming a relative signal which determines the estimated speed. When comparing the wheel speed with the relative magnitude of the signals issued slippage.

If due to excessive pressure in the wheel brake caliper is a tendency to lock (a condition that occurs when the corresponding wheel slip), the level of pressure in the caliper is held at the same level, ie it becomes impossible to increase. If the lock continues, ie the pressure is too great, the system opens the electromagnetic relief valve to reduce the pressure. Excessive fluid pump return flow is fed back into the brake cylinder. If the pressure has dropped so much that the wheel will be accelerated again, the valve closes again and the pressure remains stable. If the acceleration of the wheel transition is determined for the conditions of movement threshold, the pressure in the brake system, on the contrary, rises through the inlet solenoid valve. Thus yielding the corresponding signals from the control unit can control the hydraulic control system pressure lowering, raising or keeping it at a constant level.

Now a few words about the electronic component of the ABS.

Speed sensors - the so-called pulse transmitters. The car has four sensors, one for each wheel.

The two front sensors installed in the steering knuckle and rear - in the axis.

Speed sensor is removed with the help of gears. Ahead of them are built into the hub, rear - in the axis. The sensor consists of a magnetic core with a winding. Rotation of the ring gear, at a certain distance from the sensor changes the magnetic field under the influence of which the coil induces an alternating current. It changes the frequency in accordance with the wheel speed and the number of teeth, i.e. This frequency is proportional to the frequency of rotation.

Removal and installation of the sensors is carried out as follows:

- Switch off the ignition;

- Remove the wheel;

- In an accessible place, "snack" removes the sensor wire and attach to it a new wire. If you have no experience in connecting electrical wires, thorough insulation, corrosion protection, etc., it is better to entrust the work of art.

Elements of the ABS system either directly or indirectly affected in the works to replace the brake calipers, pads, hoses, brake disks, cables, and components of the parking brake system.