Design and Function

Summary






The vehicle is fitted with two independent braking systems, a wheel braking system and a parking brake system.

The wheel braking system is operated by the brake pedal and controls the wheel brakes on all four wheels via a hydraulic system. The hydraulic system is divided into two separate circuits, the front wheels forming one circuit and the rear wheels the other (separate axle braking system).

This means that even if one brake circuit fails, you can still brake with the other.

The braking system is fitted with:

An anti-lock braking system, ABS (Anti-lock braking system).
A system for distributing braking power between the rear wheel brakes, EBD (Electrical Brake force Distribution).
TRACS (Traction Control System) is also available as a factory fitted optional extra.

The parking brake system is controlled by the parking brake lever and acts mechanically on the wheel brakes on both rear wheels.

ABS Mark 20 is an electronic control system which is mainly designed to control the hydraulic pressure in the braking system to prevent the wheels locking when braking. By stopping the wheels locking, the ABS system prevents loss of control of the vehicle's steering and transmits as much braking effort to the road as possible.

EBD is an electronic brake force control system which acts on the rear wheels and is integrated with the ABS system. With EBD, the control module's task is to control the hydraulic pressure in the rear wheel brake circuit, if the rear wheels slip more than the front wheels when braking. This ensures that the car brakes smoothly and safely without ABS coming on. EBD replaces the reducing valve which otherwise reduces the pressure in the rear wheel brake circuit.

TRACS is an anti-wheel slip system integral to the ABS system. TRACS distributes power between the driving wheels so that the most power goes to the wheel with the best grip. The system is mainly designed to help when pulling away on slippery surfaces at up to around 40 km/h (25 mph). TRACS has only a very limited effect at speeds over 40 km/h (25 mph).

TRACS switches on every time the ignition is switched on. TRACS is switched on and off via a switch on the panel.

The ABS control module also generates a road speed signal which is sent to the instrument panel (dashboard).

ABS/EBD/TRACS has a built-in diagnostic function, Volvo Diagnostics. The signals from the system sensors are monitored continuously. If there is a fault in the system, the ABS, EBD or TRACS system is disabled partly or completely and a warning indicator comes on, on the instrument panel (dashboard). Any faults are recorded by the system control module and can be read out via Volvo Diagnostics using a Volvo System Tester connected to the DLC on the console in front of the gear lever. Volvo diagnostics can also be used to read out the values and status of the control module input and output signals. The ABS warning light flashes while the diagnostic system is activated.

Warning: ABS and EBD are not available while Volvo Diagnostics is activated. Take great care when test driving as there is a serious risk of the wheels locking when braking.

There are three braking system warning lights on the instrument panel (dashboard).






One to indicate that the brake circuit is not working. (1)
One to indicate that the parking brake is on. (2)
One to indicate that the ABS system is not working. (3)

Vehicles fitted with TRACS (4) also have a warning light which comes on if the TRACS is not working.