Circuit/System Verification
WARNING: This page is about a different car, the 2011 GMC Yukon, 2011 Chevrolet Tahoe, and 2011 Cadillac Escalade. However, it is still accessible from the selected car via links, so may be relevant.
Ignition ON, use a scan tool to observe the EBCM BMC Primary Piston Position Sensor A and B parameter while applying and releasing the brake pedal. The voltage should change between 0-5 V.