This vehicle is equipped with the BOSCH 5.3 antilock braking system.
The vehicle is equipped with the following braking systems:
The following components are involved in the operation of the above systems:
The EBCM performs one initialization test each ignition cycle. The initialization of the EBCM occurs when one set of the following conditions occur:
Both of the following conditions occur:
OR
The initialization sequence may also be commanded with a scan tool.
The initialization sequence cycles each solenoid valve and the pump motor, as well as the necessary relays for approximately 1.5 seconds to check component operation. The EBCM sets a DTC if any error is detected. The initialization sequence may be heard and felt while it is taking place, and is considered part of normal system operation.
The EBCM defines a drive cycle as the completion of the initialization sequence.
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.
The EBCM closes the inlet valve and keeps the outlet valve closed in order to isolate the system when wheel slip occurs. This holds the pressure steady on the brake so that the hydraulic pressure does not increase or decrease.
The EBCM decreases the pressure to individual wheels during a deceleration when wheel slip occurs. The inlet valve is closed and the outlet valve is opened. The excess fluid is stored in the accumulator until the return pump can return the fluid to the master cylinder.
The EBCM increases the pressure to individual wheels during a deceleration in order to reduce the speed of the wheel. The inlet valve is opened and the outlet valve is closed. The increased pressure is delivered from the master cylinder.
The Dynamic Rear Proportioning (DRP) is a control system that replaces the hydraulic proportioning function of the combination valves in the base brake system. The DRP control system is part of the operation software in the EBCM. The DRP uses active control with existing ABS in order to regulate the vehicle rear brake pressure.
The tracking control system (TCS) compares front wheel speeds to rear wheel speeds to determine if drive wheels lose traction. The TCS activates when drive wheel speed exceeds speed of non-drive wheels by a calibrated value. This allows the driver to maintain acceleration and directional stability while accelerating on low tractions surfaces.
The TCS limits wheel slip during acceleration when one or more of the drive wheels lose traction. The brake switch must be off for TCS to operate.
During a traction event, the EBCM sends a requested torque value to the PCM over the serial data link. The PCM initiates an engine torque reduction routine to slow down the drive wheels. This routine consists of ignition spark timing reduction, fuel injector cut-off and transmission shift control. The PCM also sends a torque delivered value to the EBCM over the serial data link.
If the EBCM detects a malfunction, it will disable TCS and will command the BCM to turn the TCS Off indicator On. The driver can also disable TCS, if desired by pressing the TCS switch.
The TCS is designed to limit wheel slip during acceleration when one or more of the drive wheels are accelerating too rapidly. Traction control will not have any effect on vehicle operation until the electronic brake control module (EBCM) detects one or both of the front wheels rotating faster than the rear wheels. The TCS accomplishes this by two methods, engine torque reduction and brake intervention. The two methods are used together to control wheel slip during acceleration. Both methods are described below.
The Vehicle Stability Enhancement System (VSES) is also known as the Stabilitrak Plus system, and the instrument cluster indicator lamp is labeled Stability Off. The VSES consists of a yaw/lateral accelerometer sensor, a steering angle sensor, and a brake pressure sensor working in conjunction with the EBCM.
The yaw rate sensor and lateral accelerometer sensor are both in the same module and use a reference voltage of 5 volts. The lateral accelerometer sensor operating range is 1.5 g resulting in an output range of 2.5-4.75 volts. The yaw rate sensor range is 75 degrees/seconds, resulting in a signal proportional output of 0.25-4.75 volts. Zero yaw rate is 2.5 volts. The yaw/lateral accelerometer sensor is located inside the center console, between the automatic transaxle gear selector and the console storage compartment.
The steering angle sensor sends dual CAN signals to the EBCM. The EBCM determines steering wheel position and rotation using these signals. The steering angle sensor is located in the lower left hand side of the I/P, on the bottom of the steering column.
The brake pressure sensor uses a reference voltage of 5 volts. The sensor operating range is 0.25-4.75 volts. The EBCM uses input from the brake pressure sensor for more accurate control during a VSES event.
The Variable Effort Steering system, MAGNASTEER incorporates a controller into the EBCM. The EBCM receives inputs from wheel speed sensors. The EBCM processes this information and controls the amount of current to the MAGNASTEER actuator to vary the rate of input torque required at the steering gear. A DTC is stored in the EBCM for a MAGNASTEER malfunction. A MAGNASTEER DTC C0450 will not cause the ABS or TRAC OFF indicators to go on. Refer to Variable Effort Steering System Description and Operation .
The IPC illuminates the ABS indicator when the following occurs:
The message center displays the service ABS system message when any one of many ABS-disabling DTCs is set. The EBCM sends a serial data message to the driver information center (DIC) requesting this display.
The IPC illuminates the Stability Off indicator when the electronic brake control module (EBCM) detects a malfunction in the vehicle stability enhancement system (VSES). The IPC receives a class 2 message from the EBCM requesting illumination of both the VSES indicator and the TRAC OFF indicator. The EBCM disables both the vehicle dynamic system and the traction control system.
The IPC illuminates the brake indicator when the following occurs:
The drive information center displays the service traction system message when any one of many ABS-disabling DTCs is set. The EBCM sends a serial data message to the driver information center (DIC) requesting this display.
The drive information center displays the traction active message when engine torque reduction or brake pressure application is required to maintain traction. The EBCM sends a serial data message to the driver information center (DIC) requesting this display.
The drive information center traction control off indicator when the following occurs.
The message center displays the stability system active message when a TCS or VSES event occurs. The EBCM sends a serial data message to the IPC requesting this display.
The message center displays the service stability system message when any one of many VSES-disabling DTCs is set. The EBCM sends a serial data message to the IPC requesting this display.
