EBCM Controls
WARNING: This page is about a different car, the 2010 GMC Sierra and 2010 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The EBCM controls the current to the boost valve so that pressure can be applied to the wheel brakes. The boost valve is a spool type valve which is referenced to the controlled pressure so that for a given current applied, a specific pressure is expected. The boost valve controls the pressure apply from the accumulator through the rear isolation valves directly to the rear wheel brakes, and through the front isolation valves, to the individual front pressure chambers behind the secondary pistons in the master cylinder, which in turn apply pressure to the front wheel brakes.