ABS And EBD

ABS and EBD





ABS system diagram
Bosch 5.3 system (1) is extremely compact, which reduces the number of external components to a minimum. These components include only wheel sensors, ABS warning light, and brake light switch.
EBD is integrated in the ABS control module, but has a micro-processor of its own.

Input signals
Front (6) and rear (5) wheel speed sensors send these measurements to ABS-CM to determine if a wheel is about to be blocked.
The brake light switch (7) indicates to the control module that the brakes are being affected. This puts the control module in a high state of readiness for monitoring the wheels' speed.

Output signals
The ABS warning light (2) warns the driver about malfunctions occurring in the ABS-system, which has resulted in automatic shutdown of the system.
In addition to warning for low brake fluid level, the brake fluid warning light (3) warns the driver about malfunctions in the EBD-system. This is independent of the ABS circuit. The EBD-warning is needed to warn the driver that the car may have poorer stability during braking.
DLC (4) is used to connect the diagnostics tool.
Other 'output signals' are used internally. These switch the pump relay and the relay for feed to inlet and outlet valves. The valves are controlled by then being grounded in the electrical control module. Valves and the motor are located in the hydraulic part of the ABS-unit.

Other output signals
If the car is equipped with DSA, this control module must know the wheels' speed to measure wheel spin. This information is received by the DSA control module from the ABS control module. Four communication lines are available for this purpose.
The DSA control module has no interaction or effect at all on ABS.
The combination instrument receives the wheel speed signal from right/front ABS sensor for the car's speed and driving distance.

Self-test
When the ignition is turned on, the system checks all components for their resistance values. During this check the control light is lit. The light goes off after the check (±4 seconds).
When the car starts to roll with a speed of approx. 4 km/h (2.5 mph)the pump motor is checked (and the relay). The inlet and outlet valves will also be powered up briefly.
At a speed of approx. 65 km/h (25 mph), the wheel sensors' function will be checked.
If a malfunction is detected in the system, the light stays on constantly. Troubleshooting can be done with the diagnostics tool.
The ABS system works at speeds above 4 km/h (2.5 mph).
DSA (dynamic stabilizing system) controls engine power to help to prevent the driving wheels from spinning too much. This system has nothing in common with the TRACS-system used for other Volvo models. TRACS brakes the spinning wheel to slow it down. The DSA system only uses the wheel speed information from the ABS control module.