2019 XT4 Features New Integrated Brake Control

The 2019 XT4 is the first Cadillac to use electro-hydraulic braking assist, which enhances fuel economy and takes up less space under the hood compared to a traditional vacuum-assisted power braking system.

The system uses an Integrated Brake Control (IBC) — the K160 Brake System Control Module — that interprets and converts driver brake pedal input and provides a corresponding hydraulic pressure output to activate a standard brake system. In an event of no electrical energy or a failure condition, the driver’s brake pedal input is mechanically converted to a hydraulic pressure output.

The IBC is a one-piece module that eliminates the master cylinder, vacuum pump and associated hoses while incorporating electronic stability control, traction control and an electric motor to push hydraulic fluid to the brakes at all four corners. The module is 13 lbs. (6 kg) lighter than the total weight of a conventional system.


Brake Pedal Signal

When the driver applies the brake pedal, the brake pedal position sensor reads the driver’s intent to apply the brakes. The Body Control Module (BCM) monitors the brake pedal position sensor signal and sends a high-speed serial data message to the IBC indicating the brake pedal position. (Fig. 11) By using a digital signal, brake rotor runout feedback to the driver at the brake pedal also is eliminated.

Fig. 11

During a panic stop, the system does not rely on brake pedal apply force to determine the driver’s intent but rather the speed with which the driver applies the brake pedal. Increased brake pressure is provided electronically through the IBC, which activates the antilock braking system if necessary and stops the vehicle as quickly as possible.


Brake Pad Wear Sensors

The XT4 features a new brake lining wear sensor system that estimates the remaining life of the front and rear brake pads. When the feature is active, brake pad life can be displayed on the Driver Information Center along with a percentage and distance for each axle. The IBC supplies voltage to the brake pad wear sensor, which is part of the brake caliper assembly.


Wheel Speed Sensors

The XT4 also is equipped with unique directional Wheel Speed Sensors (WSS) (Fig. 12) that can detect wheel direction as well as zero wheel speed. As the wheel spins, the WSS sends the IBC a DC square wave signal. The IBC uses the frequency of the square wave signal to calculate the wheel speed.

Fig. 12

If excessive wheel slip is monitored for greater than five seconds with a vehicle reference velocity of less than 1.9 mph (3 km/h), the traction control system will recognize this as a “stuck” condition. Once detected, the traction control system will allow additional wheel slip of 5% to help assist the vehicle. The additional wheel slip does not guarantee the vehicle will get out of the stuck condition, but is designed to assist the driver.


Power-Up-Self Test

The Brake System Control Module is able to detect many malfunctions whenever the ignition is on. However, certain failures cannot be detected unless active diagnostic tests are performed on the components. Shorted solenoid coil or motor windings, for example, cannot be detected until the components are commanded on by the Brake System Control Module. A power-up self-test is performed by the Brake System Control Module when the ignition is first turned on to verify correct operation of system components along with electrical checks of system sensors and circuits.


– Thanks to Richard Miller and Sherman Dixon

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