Base (Normal) Braking Mode

Base Braking Mode (front channel):

FRONT CHANNEL
Description
Under normal operating conditions, the brake system will operate using conventional braking by means of brake pedal force, the vacuum booster, and the master cylinder. Each front channel consists of a motor with an Expansion Spring Brake (ESB), gear driven ball-screw, piston, check valve and solenoid.

Operation
Under normal operating conditions (base brakes), the piston is held in the upmost (or "home") position. This is accomplished by turning the screw via the motor to drive the nut upwards. Once at the upmost (or "home") position, the piston is held by an ESB. While at the upmost position, the piston also unseats the check valve via a protrusion on the piston. Two paths are then available to transfer braking pressure to the wheel: (1) through the modulator, around the check valve, and out to the wheel, (2) through the modulator, past the normally open solenoid, and out to the wheel. The solenoid in the front circuits provides an alternate brake pressure path to the wheel. With this arrangement, if the ABS were to lose power or malfunction with the piston not in its upmost position, a redundant brake fluid path is available.

REAR CHANNEL
Description
The hydraulically isolated rear wheel channels operate in a similar manner except both are controlled together with one motor and there is no solenoid.

Operation
While at the upmost position, the piston unseats the check valve via a protrusion on the piston. With the rear wheels, only one path is then available to transfer braking pressure to the rear wheels: through the modulator, around the check valve, and out to the rear wheels. There is no rear solenoid due to the nature of the braking system. The majority of braking is accomplished with the front brakes. If an ABS failure were to occur that affected the operation of the rear base brakes, a Diagnostic Trouble Code (DTC) would be stored and the Electronic Brake Control Module (EBCM) would turn ON both the amber ABS indicator lamp and the red BRAKE warning lamp.