This vehicle is equipped with the BOSCH 8.0 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 the vehicle speed is greater than 16 km/h (10 mph).
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 mechanical proportioning valve 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's rear brake pressure.
The red brake warning indicator is illuminated when the dynamic rear proportioning function is disabled.
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 ECM/TCM over the serial data link. The ECM/TCS 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 ECM/TCM 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 LED Off. The driver can also disable TCS, if desired by pressing the TCS switch.
The instrument panel cluster illuminates the ABS indicator when the following occurs:
The IPC illuminates the brake indicator when the following occurs:
The IPC illuminates the low brake fluid indicator in the message center when the IPC receives a low signal from the low brake fluid switch.
The LOW TRACTION message on the Driver Information Center will come On whenever the TCS is in operation. The message will remain On for 3-4 seconds after the TCS event is complete. The message does NOT operate during an ABS event.
This test allows the technician to flash the TCS LED On and Off with the Scan tool:
Whenever the TCS switch LED is illuminated TCS is available. This will default ON every time the vehicle is started. The TCS can be disabled by pressing the switch. The TCS Switch and LED is controlled by the BCM.
