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Valve block, ABS function

Valve block, ABS function


The valve block, which is an integral part of the hydraulic unit, modulates the brake pressure to the calipers when ABS and TCS braking is activated.

The valve block contains 12 solenoid valves: four inlet valves, four outlet valves, two pressure increase valves and two pressure relief valves. These are arranged as follows: one inlet and one outlet valve for each of the four wheels and one pressure increase and one pressure relief valve for each of the front wheels. The pressure increase and pressure relief valves are activated only in TCS mode and are described in .

In the rest position, the inlet valve is open and the outlet valve closed. During ABS control the inlet valve is closed to maintain a constant pressure. The outlet valve opens at the same time as the return pump starts.

The valve block incorporates an accumulator chamber and a pressure chamber for each brake circuit. The accumulator chamber, which is located between the outlet valve and the return pump, accumulates the brake fluid until the return pump starts.

The function of the pressure chamber, which is located between the return pump and master cylinder, is to dampen both noise and pressure fluctuations when the return pump is operating (ABS mode).

Diagnostics

The control module performs a valve test each time the ignition is switched on. This test takes place at the same time as the pump-motor test and the valves are actuated for 20 ms.

A fault in the left-hand front inlet/outlet valves will set diagnostic trouble code C2450.

A fault in the right-hand front inlet/outlet valves will set diagnostic trouble code C2455.

A fault in the left-hand rear inlet/outlet valves will set diagnostic trouble code C2415.

A fault in the right-hand front inlet/outlet valves will set diagnostic trouble code C2485.

A fault in the left-hand front pressure increase valve will set diagnostic trouble code C0141.

A fault in the left-hand front pressure-reducing valve will set diagnostic trouble code C0146.

A fault in the right-hand front pressure increase valve will set diagnostic trouble code C0151.

A fault in the right-hand front pressure-reducing valve will set diagnostic trouble code C0156.

In all the above cases, the TCS and ABS functions will be disabled and the warning lamps for ABS, brakes and TCS OFF will light up as well as the central warning lamp.