This vehicle is equipped with the Continental Teves MK-70 antilock braking system.
The following components are involved in the operation of the above system.
| • | Electronic brake control module (EBCM)--The EBCM controls the system functions and detects failures. |
| | The EBCM contains the following components: |
| - | System relay --The system relay is internal to the EBCM. The system relay is energized when the ignition is ON. The system relay supplies battery positive voltage to the solenoid valves and to the pump motor. |
| - | Solenoids--The solenoids are commanded by the EBCM to operate the appropriate valves in the brake pressure modulator valve. |
| • | Brake pressure modulator valve (BPMV)--The BPMV uses a 4-circuit configuration to direct fluid to the left front, right front, left rear, and right rear wheels independently. |
| | The BPMV contains the following components: |
| - | Four inlet valves, one for each hydraulic circuit |
| - | Four outlet valves, one for each hydraulic circuit |
| • | The wheel speed sensor receives a 12-volt power supply voltage from the electronic brake control module (EBCM) and provides an output signal to the EBCM. As the wheel spins, the wheel speed sensor sends the EBCM a DC square wave signal. The EBCM
uses the frequency of the square wave signal to calculate the wheel speed. |
Initialization and Self-Test Sequence
The electronic brake control module (EBCM) performs one initialization test each ignition cycle. The initialization of the EBCM occurs when the following conditions are met:
| • | The bulb check has been completed. |
| • | Vehicle speed is greater than 20 km/h (12 mph). |
The initialization and Self-Test sequence briefly cycles each solenoid and the pump motor to verify proper operation of the components. The EBCM sets one or more DTCs in accordance with any malfunction that is detected.
Antilock Brake System
When wheel slip is detected during a brake application, the ABS enters antilock mode. During antilock braking, hydraulic pressure in the individual wheel circuits is controlled to prevent any wheel from slipping. A separate hydraulic line and specific
solenoid valves are provided for each wheel. The ABS can decrease, hold, or increase hydraulic pressure to each wheel brake. The ABS cannot, however, increase hydraulic pressure above the amount which is transmitted by the master cylinder during braking.
During antilock braking, a series of rapid pulsations is felt in the brake pedal. These pulsations are caused by the rapid changes in position of the individual solenoid valves as the electronic brake control module (EBCM) responds to wheel speed sensor
inputs and attempts to prevent wheel slip. These pedal pulsations are present only during antilock braking and stop when normal braking is resumed or when the vehicle comes to a stop. A ticking or popping noise may also be heard as the solenoid valves cycle
rapidly. During antilock braking on dry pavement, intermittent chirping noises may be heard as the tires approach slipping. These noises and pedal pulsations are considered normal during antilock operation.
Vehicles equipped with ABS may be stopped by applying normal force to the brake pedal. Brake pedal operation during normal braking is no different than that of previous non-ABS systems. Maintaining a constant force on the brake pedal provides the shortest
stopping distance while maintaining vehicle stability.
Pressure Hold
The electronic brake control module (EBCM) closes the isolation valve and keeps the dump valve closed in order to isolate the slipping wheel when wheel slip occurs. This holds the pressure steady on the brake so that the hydraulic pressure does not increase
or decrease.
Pressure Decrease
If a pressure hold does not correct the wheel slip condition, a pressure decrease occurs. The electronic brake control module (EBCM) decreases the pressure to individual wheels during deceleration when wheel slip occurs. The isolation valve is closed and
the dump valve is opened. The excess fluid is stored in the accumulator until the pump can return the fluid to the master cylinder or fluid reservoir.
Pressure Increase
After the wheel slip is corrected, a pressure increase occurs. The electronic brake control module (EBCM) increases the pressure to individual wheels during deceleration in order to reduce the speed of the wheel. The isolation valve is opened and the dump
valve is closed. The increased pressure is delivered from the master cylinder.
Dynamic Rear Proportioning (DRP)
The dynamic rear proportioning (DRP) is a control system that replaces the hydraulic proportioning function of the mechanical proportioning valve in the base brake system. The DRP control system is part of the operation software in the electronic brake
control module (EBCM). The DRP uses active control with existing ABS in order to regulate the vehicle's rear brake pressure.
The red brake warning indicator is illuminated when the dynamic rear proportioning function is disabled.
Brake Warning Indicator
The instrument panel cluster (IPC) illuminates the brake warning indicator when any of the following occurs.
| • | The BCM detects that the park brake is engaged. |
| • | The BCM detects a low brake fluid condition. The BCM sets a DTC and sends a GMLAN message to the IPC requesting illumination of the brake warning indicator. |
| • | The IPC performs the bulb check. |
| • | An ABS disabling malfunction also disables dynamic rear proportioning (DRP). |
ABS Indicator
The instrument panel cluster (IPC) illuminates the ABS indicator when any of the following occurs.
| • | The electronic brake control module (EBCM) detects an ABS disabling malfunction. The EBCM sends GMLAN message to the IPC requesting illumination. |
| • | The IPC performs the bulb check. |
| • | The IPC detects a loss of GMLAN communications with the EBCM. |
