New components:

The electronic stabilization program hydraulic pump for traction control -V156- and the sender 1 for brake booster -G201- are on the left side of the engine compartment beneath the ABS hydraulic unit -N55-. 

The ABS hydraulic unit -N55- with ABS return flow pump -V39- are assisted by the Hydraulic pump for traction control -V156-. This enables the system to rapidly build up the required brake fluid pressure in the wheel brake cylinders.

Fig 1: Identifying Electronic Stabilization Program Hydraulic Pump For Traction Control

Courtesy of AUDI OF AMERICA, INC.

Do not loosen the bolts securing the individual components of the ABS hydraulic unit -N55- and the Hydraulic pump for traction control -V156-. The Hydraulic pump for traction control -V156- and the Sender 1 for brake booster -G201- form a single unit and must always be replaced together if necessary.

The Sender 1 for brake booster -G201- measures the fluid pressure generated in the brake system.