For 1990-2009 cars

The vehicle is equipped with the following braking systems:

• | Antilock Brake System (ABS)

• | Dynamic Rear Proportioning (DRP)

• | Vehicle Stability Enhancement System (VSES)

The following components are involved in the operation of the above systems.

Electronic brake control module (EBCM) controls the system functions and detects failures.

The EBCM contains the following components:

• | Internal pump relay-The relay is energized to supply B+ to the hydraulic pump.

• | 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 contains the hydraulic valves and pump motor that are controlled electrically by the EBCM. The BPMV uses a 4 circuit configuration with a diagonal split. The BPMV directs fluid from the reservoir of the master cylinder to the left front and right rear wheels and fluid from the other reservoir to the right front and left rear wheels. The diagonal circuits are hydraulically isolated so that a leak or malfunction in one circuit will allow continued braking ability on the other.

• | The BPMV contains the following components:

- | Pump motor

- | Inlet valves (one per wheel)

- | Outlet valves (one per wheel)

- | Master cylinder isolation valves (one per drive wheel)

- | Prime valves (one per drive wheel)

• | The wheel speed sensor receives B+ from the electronic brake control module (EBCM) and monitors the wheel speed by providing a DC square wave signal back to the module. As the wheel spins, the EBCM uses the frequency of the square wave signal to calculate the wheel speed.

• | Stability control switch-The stability control can be manually disabled using the stability control switch.

• | Stop lamp switch-The EBCM uses the stop lamp switch as an indication that the brake pedal is applied.

• | Lateral accelerometer sensor-The EBCM uses the lateral accelerometer sensor as an indication of the lateral acceleration of the vehicle.

• | Yaw rate sensor-The EBCM uses the yaw rate sensor as an indication of the yaw rate of the vehicle.

• | Steering wheel position sensor (SWPS)-The EBCM uses the SWPS as an indication of the position and rotation of the steering wheel.

### Vehicle Stability Enhancement System (VSES)

The vehicle stability enhancement system (VSES) adds an additional level of vehicle control to the ABS.

Yaw rate is the rate of rotation about the vehicle's vertical axis. The VSES is activated when the electronic brake control module (EBCM) determines that the desired yaw rate does not match the actual yaw rate as measured by the yaw rate sensor.

The desired yaw rate is calculated from the following parameters:

• | The position of the steering wheel

• | The speed of the vehicle

• | The lateral, or sideways acceleration of the vehicle

The difference between the desired yaw rate and the actual yaw rate is the yaw rate error, which is a measurement of over steer or under steer. If the yaw rate error becomes too large, the EBCM attempts to correct the vehicle's yaw motion by applying differential braking to the appropriate wheel. The amount of differential braking applied to the left or right front wheel is based on both the yaw rate error and side slip rate error.

The VSES activations generally occur during aggressive driving, in turns or on bumpy roads without much use of the accelerator pedal. When braking during VSES activation, the pedal pulsations feel different than the ABS pedal pulsations. The brake pedal pulsates at a higher frequency during VSES activation.

### Initialization Sequence

The electronic brake control module (EBCM) performs 1 initialization test each ignition cycle when the following conditions are met. The initialization of the EBCM occurs when 1 set of the following conditions occur:

• | The ignition is ON.

• | The bulb check has been completed.

• | Vehicle speed is greater than 13 km/h (8 mph).

The initialization sequence briefly cycles each solenoid and the pump motor to verify proper operation of the components. The EBCM sets one or more DTCs when a malfunction 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 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.

### Vehicle Stability Enhancement System (VSES)

The vehicle stability enhancement system (VSES) adds an additional level of vehicle control to the electronic brake control module (EBCM).

Yaw rate is the rate of rotation about the vehicles vertical axis. The VSES is activated when the EBCM determines that the desired yaw rate does not match the actual yaw rate as measured by the yaw rate sensor.

The desired yaw rate is calculated from the following parameters:

• | The position of the steering wheel

• | The speed of the vehicle

• | The lateral, or sideways acceleration of the vehicle

The difference between the desired yaw rate and the actual yaw rate is the yaw rate error, which is a measurement of over steer or under steer. If the yaw rate error becomes too large, the EBCM attempts to correct the vehicle's yaw motion by applying differential braking to the appropriate wheel. The amount of differential braking applied to the left or right front wheel is based on both the yaw rate error and side slip rate error.

The VSES activations generally occur during aggressive driving, in turns or on bumpy roads without much use of the accelerator pedal. When braking during VSES activation, the pedal pulsations feel different than the ABS pedal pulsations. The brake pedal pulsates at a higher frequency during VSES activation.

### 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 part of the BPMV that regulates the brake pressure to the vehicles rear brakes.

### Brake Warning Indicator

The instrument panel cluster (IPC) illuminates the brake warning indicator when any of the following occurs.

• | The IPC detects that the brake fluid level switch is closed.

• | The body control module (BCM) detects the park brake switch is closed, and sends a serial data message to the IPC to illuminate the brake warning indicator.

• | The IPC performs the display test for approximately 3 seconds at the start of each ignition cycle.

• | The EBCM detects a malfunction and send a serial data message to the IPC to illuminate the brake warning indicator.

### ABS Indicator

The instrument panel cluster (IPC) illuminates the ABS indicator when any of the following occurs:

• | The electronic brake control module (EBCM) detects malfunction and sends a serial data message the IPC to illuminate the brake warning indicator.

• | When you start your vehicle, the ABS indicator will illuminate briefly during the IPC display test.

• | The IPC detects a loss of communication with the EBCM.

### Stability Control Indicator

The instrument panel cluster (IPC) illuminates the stability control indicator when any of the following occurs:

• | The electronic brake control module (EBCM) detects a malfunction and sends a serial data message the IPC to illuminate the brake warning indicator.

• | When you start your vehicle, the ABS indicator will illuminate briefly during the IPC display test.

• | The IPC detects a loss of communication with the EBCM.

### ECE 13 Response

When a malfunction is corrected, and the code is cleared, the vehicle needs to be driven over 15 mph for the electronic brake control module (EBCM) to enable the ABS and send a serial data message the instrument panel cluster (IPC) to turn OFF the ABS indicator.