Freelander System Description and Operation
BRAKES
70-4
DESCRIPTION AND OPERATION
Mechanical Brake Switch
A mechanical brake pedal switch is used to illuminate the stop/brake lamps on the vehicle because of its high current
carrying/switching capabilities. It is also used to input the status of the brake pedal to the ABS ECU. This switch is a
double contact switch where the Brake Lamp Switch (BLS) contacts are open and the Brake Test Switch (BTS)
contacts are closed when the brake pedal is at rest. When the pedal is depressed, the BLS contacts close and BTS
contacts open, supplying 12 volts to the brake/stop lamps and indicating to the ABS ECU that the pedal has been
operated. When the pedal is depressed there is a time when both the BLS and the BTS contacts are closed, which
allows the ABS ECU to perform a plausibility check on the switch. The switch used is a carry over from the Range
Rover.
A Hall effect brake pedal position sensor is installed adjacent to the mechanical brake switch. This is not used by the
brake system but by other system ECU's which are not compatible with the outputs from a mechanical switch.
Brake Fluid Level Switch
The Brake Fluid Level Switch (BFLS) is a Reed switch located in the brake fluid reservoir. The BFLS is connected to
the ABS ECU and to earth. The BFLS is closed when the brake fluid level is above the minimum limit. If the brake
fluid level decreases below the minimum limit, the BFLS opens and the ABS ECU sends a CAN message to the
instrument pack to activate the brake warning lamp.
Hill Descent Control Relay and Switch
The HDC relay is located inside the engine compartment fusebox. The HDC switch is a latching switch mounted on
the gear lever surround.
Accelerometer
The accelerometer (sometimes known as the "G" sensor) is mounted near the centre-line of the vehicle alongside the
handbrake lever. It provides information to the ABS ECU regarding vehicle longitudinal acceleration.
The ABS ECU uses the input from the accelerometer to corroborate the inputs from the ABS sensors, e.g. if all four
wheels are spinning, the input from the accelerometer enables the ABS ECU to determine the true speed of the
vehicle.
Front Brakes
The front brakes each comprise a hub mounted, single piston caliper assembly and a vented disc. The inboard side
of the disc is protected by a mudshield.
When hydraulic pressure is supplied to the caliper, the piston extends and forces the inner pad against the disc. The
caliper body reacts and slides on the guide pins to bring the outer pad into contact with the disc.