System Overview

System overview

Introduction
Brake control system Mark 25E1
The Mark 25E1 brake control system with the brake control module (BCM) is an electronic control system that prevents wheel lock-up during braking (ABS). Preventing wheel lock-up makes it possible to maintain steering control and maximize braking effect.

The brake control system comprises:
- Anti-lock Braking System (ABS)
- Electrical Brake force Distribution (EBD) at the rear wheel brakes.
- Dynamic Stability and Traction Control system (DSTC)
- Emergency Brake Assistance (EBA)

The Mark 25E1 brake system also includes a number of functions to assist the driver in various braking situations.
- The brake system pressurization function fills the brake system with brake fluid, which minimizes the distance between the brake disc and brake pad.
- The hydraulic pump activation function helps the brake system increase brake pressure by activating the hydraulic pump when the vacuum pressure from the brake servo is insufficient.
Other vehicle systems can send a request to the Mark 25E1 brake control system to activate certain other brake functions. The following control modules can request brake function from the brake control module (BCM):
- Forward sensing module (FSM). The system uses a forward-aimed radar that detects whether there are any objects within a predefined area in front of the vehicle while driving. If the system registers any object or obstacle, a request is sent to the brake control module (BCM) to decelerate the vehicle.
- Park brake module (PBM). The system is an electrically operated parking brake. If the driver activates the parking brake while driving, the park brake module (PBM) requests the braking function from the brake control module (BCM).
- Closing velocity module (CVM) (XC60 and S60 (11-)). The system uses a forward-sensing lidar, works like a radar but uses light instead of electromagnetic waves, which during travel at low speeds below senses if an object is within a predefined area in front of the vehicle. If the system registers any object or obstruction, a request is sent to Brake control module (BCM) to brake the vehicle.

Control module




The control module is mounted with the hydraulic unit as a unit and is located on the cowl panel in the engine compartment. The electrical valve coils for the different hydraulic valves are integrated into the control module.
The most important function of the control module is to process the signals from the various system sensors as well as those from other control modules an to use the signals to regulate the hydraulic pump and the electromagnetic hydraulic valves (intake and outlet valves) in the hydraulic unit during:
- ABS control
- EBD control
- AYC control
- EBA control
The control module communicates with directly connected components and other control modules via the CAN network.
The control module checks its calculations as well as all output and input signals with built-in diagnostics function.
When the vehicle is started and driven off the control module checks that the signal from the wheel sensors is OK. When the ignition is turned on the control module checks the pump motor's and the hydraulic valves' function by briefly activating the components. The hydraulic pump and the valves can be heard, which is completely normal.
The ABS function can be activated once vehicle speed exceeds approx. 7 km/h (4.3 mph). The traction control function, however, is operable right from the start. The control module also performs a start-up test, at which time the warning lamps that are linked to the functions in the system are activated in the driver information module.
If the control module detects a fault, it stores a diagnostic trouble code in its internal memory. A number of values that were frozen at the time the fault occurred are stored at the same time. Depending on the severity of the fault, certain functions may be partially or completely disengaged. A warning lamp lights in the driver information module (DIM) to inform the driver that a fault has occurred. A warning or information text will also be shown in the display in the driver information module (DIM). The text displayed is determined by the type of fault (see the table). Diagnostic trouble codes and frozen values can be read off using the diagnostic tool via the data link connector in the vehicle.






Signals
The table below summarizes the input signals to and output signals from the brake control module (BCM). The signal types are divided into directly connected signals, serial communication and CAN communication. The illustration below displays the same information with the Volvo component designations.