This vehicle is equipped with the Continental Teves MK 25E antilock braking system.
The vehicle is equipped with the following braking systems:
| • | Antilock Brake System (ABS) |
| • | Electronic Brake Force Distribution (EBD) |
| • | Traction Control System (TCS) |
| • | Vehicle Stability Enhancement System (VSES) (w/JL4) |
The following components are involved in the operation of the above systems:
| • | Electronic Brake Control Module (EBCM)--The EBCM controls the system functions and detects failures. |
| | The EBCM contains the following components: |
| - | Motor Relay--The motor relay is energized when the ignition is ON and no ABS DTCs are present. It supplies battery positive voltage to the pump motor. |
| - | Valve Relay--The valve relay is energized when the ignition is ON and no ABS DTCs are present. It supplies battery positive voltage to the solenoid valves. |
| • | 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. |
| | Important: There is a rubber isolator located under the BPMV and on the mounting studs. The rubber isolators protect the BPMV and the EBCM from vehicle vibrations.
|
| • | The BPMV contains the following components: |
| - | ABS pump Motor and pump |
| - | Inlet Valves (one per wheel) |
| - | Outlet Valves (one per wheel) |
| - | Master Cylinder Isolation Valves (one per drive wheel) |
| - | Prime Valves (one per drive wheel) |
| - | A master cylinder pressure sensor |
| • | 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. |
| • | Traction Control Switch--The TCS is manually disabled or enabled using the traction control switch. |
| • | Stoplamp Switch--The EBCM uses the stoplamp switch as an indication that the brake pedal is applied. |
| • | Lateral Accelerometer Sensor (w/JL4)--The EBCM uses the lateral accelerometer sensor as an indication of the lateral acceleration of the vehicle. |
| • | Yaw Rate Sensor (w/JL4)--The EBCM uses the yaw rate sensor as an indication of the yaw rate of the vehicle. |
| • | Steering Wheel Position Sensor (SWPS) (w/JL4)--The EBCM uses the SWPS as an indication of the position and rotation of the steering wheel. |
Initialization Sequence
The EBCM performs 1 initialization test each ignition cycle. The initialization of the EBCM occurs when 1 set of the following conditions occur:
Both of the following conditions occur:
| • | The EBCM detects that there is a minimum of 500 RPM from the ECM via a serial data message. |
| • | The stop lamp switch is not applied. |
OR
Both of the following conditions occur:
| • | The vehicle speed is greater than 16 km/h (10 mph). |
| • | The stop lamp switch is applied. |
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.
Antilock Brake System (ABS)
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.
Pressure Hold
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.
Pressure 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.
Pressure Increase
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.
Electronic Brake Force Distribution (EBD)
The electronic brake force distribution (EBD) is a control system that replaces the hydraulic proportioning function of the mechanical proportioning valve in the base brake system. The EBC control system is part of the operation software in the EBCM. The
EBC 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.
Traction Control System (TCS)
When drive wheel slip is noted while the brake is not applied, the electronic brake control module (EBCM) will enter traction control mode.
First, the EBCM requests the engine control module (ECM) to reduce the amount of torque to the drive wheels via the serial data. The ECM reduces torque to the drive wheels by retarding spark timing and turning off fuel injectors. The ECM reports the amount
torque delivered to the drive wheels via the serial data circuit.
If the engine torque reduction does not eliminate drive wheel slip, the EBCM will actively apply the drive wheel brakes. During traction control braking, hydraulic pressure in each drive wheel circuit is controlled to prevent the drive wheels from slipping.
The master cylinder isolation valve closes in order to isolate the master cylinder from the rest of the hydraulic system. The prime valve then opens in order to allow the pump to accumulate brake fluid in order to build hydraulic pressure for braking. The drive
wheel inlet and outlet solenoid valves then open and close in order to perform the following functions:
Vehicle Stability Enhancement System (VSES)
The vehicle stability enhancement system (VSES) adds an additional level of vehicle control to the EBCM.
Yaw rate is the rate of rotation about the vehicle's 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 oversteer or understeer. 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.
ECE 13 Response
The electronic brake control module (EBCM) illuminates the ABS indicator when a malfunction which disables ABS is detected. Usually, the ABS indicator is turned OFF during the following ignition cycle unless the fault is detected during that ignition cycle.
However, the setting of a wheel speed sensor related DTC causes the ABS indicator to remain illuminated during the following ignition cycle until the vehicle is operated at a speed greater than 13 km/h (8 mph). This allows the EBCM to verify that
no malfunction exists, before turning OFF the ABS indicator. This reaction occurs even if the ABS indicator turns OFF when the scan tool is used to clear the DTCs. When repairing these vehicles, it is important to ensure that the ECE 13 response has occurred
and that the ABS indicator does not illuminate after returning the vehicle to the customer. It is also important to verify that ECE 13 is not the cause of an ABS indicator which is illuminated when no DTCs are set, before attempting to diagnose other
possible causes.
Driver Information Indicators and Messages
The following indicators are used to inform the driver of several different factors.
Brake Warning Indicator
The instrument panel cluster (IPC) illuminates the brake warning indicator when the following occurs.
| • | The electronic brake control module (EBCM) detects that the park brake is engaged. The IPC receives a serial data message from the EBCM requesting illumination. |
| • | The instrument panel cluster (IPC) detects a low brake fluid condition and the IPC will illumination the brake warning indicator. |
| • | The IPC performs the bulb check. |
| • | The EBCM detects an ABS-disabling malfunction which also disables electronic brake force distribution (EBD) and sends a serial data message to the IPC requesting illumination. |
Stability System Indicator
The IPC illuminates the stability system caution indicator when one or more of the following conditions exists. The EBCM sets any one of many VSES-disabling DTCs. The EBCM sends a serial data message to the IPC requesting illumination.
ABS Indicator
The instrument panel cluster (IPC) illuminates the Antilock Brake System (ABS) indicator when the following occurs:
| • | The electronic brake control module (EBCM) detects a malfunction with the antilock brake system. The IPC receives a serial data message from the EBCM requesting illumination. |
| • | The IPC performs the displays test at the start of each ignition cycle. The indicator illuminates for approximately 5 seconds. |
| • | The IPC detects a loss of serial data communications with the EBCM. |
Traction Control System Indicator
TRAC OFF
The instrument panel cluster (IPC) illuminates the TRAC OFF indicator when the following occurs:
| • | The electronic brake control module (EBCM) inhibits the traction control system due to a malfunction in the traction control system. The IPC receives a serial data message from the EBCM requesting illumination. |
| • | The Body Control module (BCM) detects that the traction control switch has been pressed (signal circuit is low). The Body Control module (BCM) sends a serial data message to the EBCM in order to disable traction control. The IPC receives a serial
data message from the EBCM requesting illumination. The BCM sends a serial data message to the radio in order to activate an audible warning. |
