7. Hydraulic unit · The hydraulic unit essentiallyconsists of fast-

911 Carrera (996) Anti-lock Brake System (ADS) 7. Hydraulic unit The hydraulic unit essentiallyconsists of fast- switching electromagnetic valves and a return pump. Regardless of the pressure in the brake master cylinderI the hydraulic unit can change the fluid pressure to the wheel brake cylinders (holding or reducing pressure). Increasingthe pressure above that of the brake master cylinder is not possible, however. The ABS 5.3 hydraulic unit has three hydraulic outputs (3-channel system) and six electromagnetic valves (three inlet and three outlet valves), The ABS / TC 5.3 hydraulic unit has four hydraulic outputs (4-channel system) and ten electromagnetic valves (four inlet valves / four outlet valves, one switch-overvalve and one intake valve). The intake and switch-overvalves are required so that the return pump can perform two tasks: I. Return flow to the brake master cylinder (pressure reduction)for ABS control. II. Supply(pressure increase)to the right or left rear-wheelbrake cylinder for TC control (ABD control). In the case of ABS control at the rear axle, the solenoid valves for both rear wheels are actuated in parallel (joint control as in Solo ABS control (3-channelsystem)). 45 Function of individual components 45 -9 Printed in Germany, 1997 996451.