Anti Lock Brake Info Series 2 (More then you ever wanted)

[Joey]

General
The brakes consist of front and rear disc brakes operated by a diagonally split, dual circuit hydraulic system with vacuum servo power assistance. The system incorporates the following control functions as standard on all models:
• Anti-lock Brakes (ABS) , to prevent road wheels locking during brake application.
• Electronic Brake Distribution (EBD) , to control distribution of hydraulic pressure between front and rear axles. Replaces mechanical pressure limiting valve of previous systems.
• Electronic Traction Control (ETC) , to maintain even torque distribution to the road wheels.
• Hill Descent Control (HDC) , to provide controlled descent ability in off road conditions.




Hydraulic system schematic

For normal brake operation, brake pedal movement is assisted by the brake servo assembly and transmitted to the master cylinder assembly. The master cylinder assembly converts brake pedal movement to hydraulic pressure. Primary and secondary brake pipe circuits supply the hydraulic pressure to the brakes via the ABS modulator: the primary circuit supplies the front left and rear right brakes; the secondary circuit supplies the front right and rear left brakes. Vacuum for the brake servo assembly is obtained from the engine inlet manifold (V8 models) or a vacuum pump (diesel models), through a vacuum line and non return valve. To reduce operating noise, sleeving is installed on some of the brake pipes in the engine compartment and the pipes are located in sprung pipe clips.
For all control functions, the ABS modulator regulates the hydraulic pressure to the brakes to control the speed of all four wheels, either individually or in axle pairs. Operation of the ABS modulator is controlled by the Self Leveling and Anti-lock Braking Systems (SLABS) ECU. The SLABS ECU also operates warning indications in the instrument pack to provide the driver with status information on each function.

Brake Servo Assembly
The brake servo assembly provides power assistance to reduce the pedal load when braking. If the brake servo assembly fails, the hydraulic system still functions but will require greater brake pedal effort due to the lack of vacuum assistance.

Two integral tie bolts attach the brake servo assembly to the pedal and bracket assembly on the engine bulkhead. The master cylinder assembly is attached to the forward ends of the tie bolts.

The brake servo assembly consists of a circular housing which contains two diaphragms, a central plate, a control valve assembly, input and output push rods and a filter. The input push rod is connected to the brake pedal. The output push rod locates in the primary piston of the master cylinder. A protective gaiter is installed on the control valve assembly where it extends from the rear of the housing. A non return valve, installed in a port in the front face of the housing, is connected to a vacuum line from the engine.

The control valve assembly consists of a valve body containing a valve, a piston, a valve spring and an input rod spring. The valve controls a vacuum port in the valve body. The piston controls an air inlet port between the valve and the piston. A reaction disc and a ratio disc separate the piston from the output push rod. A guide tube on the front of the valve body is attached to the front diaphragm and supported in a bush in the central plate. A return spring locates in the open end of the guide tube.

The two diaphragms and the central plate separate the interior of the housing into four sealed chambers. The chambers at the front of the diaphragms are connected together through fixed passages in the valve assembly. The chambers at the rear of the diaphragms are connected together through the interior of minor diaphragms on the tie bolts.

Brakes off
With the brake pedal released, the piston in the control valve assembly positions the valve so that the vacuum port is open and the two pairs of chambers are connected together. When the engine is running air is evacuated through the vacuum line and non return valve, creating a partial vacuum in all four chambers. When the engine stops, the non return valve closes to maintain the partial vacuum and, on V8 models, prevent fuel vapor entering the brake servo.



Section through brake servo assembly - brakes off

Brakes on
When the brake pedal is pressed, the input push rod and the piston initially move forward in the valve body. The valve body and output rod then move with the input rod, against resistance from the return spring, to transmit the brake pedal force to the master cylinder assembly.

During the initial movement of the piston, the valve, assisted by the valve spring, moves with the piston and closes the vacuum port to isolate the chambers at the rear of the diaphragms from the vacuum source. Further movement of the input push rod causes the piston to move away from the valve and open the air inlet port. This allows a restricted flow of filtered ambient air through the air inlet port, which creates a servo pressure in the chambers at the rear of the diaphragms. Force from the resultant pressure differential across the diaphragms is transmitted through the valve body to the output push rod, augmenting the pressure being applied by the brake pedal. The force produced by the diaphragms, in proportion to the input force, i.e. the boost ratio, is 5.6:1. The boost ratio remains constant, as the input force from the brake pedal increases, until the limit of assistance is reached when servo pressure is equal to ambient pressure.

Brakes held on
When the brake pedal effort is constant, opposing pressures cause the reaction disc to extrude onto the ratio disc, which moves the piston against the valve to close the air inlet port. This prevents any further increase in servo pressure and maintains a constant output force to the master cylinder assembly.

Brakes released
When the brake pedal is released, the input rod spring moves the input rod and piston rearwards within the valve body to close the air inlet port and open the vacuum port. The air from the chambers at the rear of the diaphragms is then evacuated, through the vacuum port and the chambers at the front of the diaphragms, to restore a partial vacuum in all four chambers. Simultaneously, the return spring moves the valve body, diaphragms, output rod and input rod rearwards to return them to their brakes off position.

Vacuum pump (diesel models only)


As the diesel engine air inlet system does not produce sufficient depression to operate the brake servo assembly, an engine driven vacuum pump is installed.
The vacuum pump is integrated with the engine alternator and driven by the auxiliary drive belt. The pump is a rotary vane type, lubricated and cooled by engine oil supplied through a pipe connected to the engine block and returned through a pipe connected to the engine oil sump. Air extracted from the brake servo assembly is vented into the oil sump with returning lubricating oil.

Master Cylinder Assembly


The master cylinder assembly produces hydraulic pressure to operate the brakes when the brake pedal is pressed.
The assembly is attached to the front of the brake servo assembly, and comprises a cylinder containing two pistons in tandem. The rear piston produces pressure for the primary circuit and the front piston produces pressure for the secondary circuit. A brake fluid reservoir is installed on top of the cylinder. The reservoir is internally divided to provide an independent supply of fluid to each brake circuit, and so prevent a single fluid leak from disabling both primary and secondary brake circuits. Should a failure occur in one circuit, the remaining circuit will still operate effectively, although brake pedal travel and vehicle braking distances will increase. If the fluid level in the reservoir is too low, a float operated switch in the reservoir filler cap connects an earth to the instrument pack, which illuminates the brake warning lamp.

Brakes applied
When the brake pedal is pressed, the output rod in the brake servo assembly pushes the primary piston along the cylinder bore. This produces pressure in the primary pressure chamber which, in conjunction with the primary spring, overcomes the secondary spring and simultaneously moves the secondary piston along the cylinder bore. The initial movement of the pistons, away from the piston stops, closes the primary and secondary center valves. Further movement of the pistons then pressurizes the fluid in the primary and secondary pressure chambers, and thus the brake circuits. The fluid in the chambers behind the pistons is unaffected by movement of the pistons and can flow unrestricted through the feed holes between the chambers and the reservoir.

Brakes released
When the brake pedal is released, the primary and secondary springs push the pistons back down the bore of the cylinder. The rapid movement of the pistons cause partial vacuums to form in the pressure chambers, which opens the center valves and allows fluid to circulate unrestricted between the two hydraulic circuits and the reservoir. When the pistons reach the brakes off position, the center valves are held open by the piston stops.

ABS modulator schematic
The ABS modulator is a 4 channel unit that controls the supply of hydraulic pressure to the brakes in response to inputs from the SLABS ECU. The modulator is attached by three mounting bushes to a bracket on the LH inner front wing, and connected to the primary and secondary hydraulic circuits downstream of the master cylinder assembly. Three electrical connectors link the ABS modulator to the vehicle wiring.

Passages within the ABS modulator, separated into primary and secondary circuits, connect to the various internal components that control the supply of hydraulic pressure to the brakes:
• Shuttle valves and non return valves control the flow through the internal circuits.
• Shuttle valve switches, connected in series to the SLABS ECU, provide a brakes on/off signal.
• A damper chamber and restrictor are included in each circuit to refine system operation.
• Inlet and outlet solenoid valves control the flow to the individual brakes.
• An expansion chamber is connected to each circuit to absorb pressure.
• A return pump is connected to both circuits to provide a pressure source. The ABS modulator has three operating modes: Normal braking, ABS braking and active braking.
Normal braking mode
When the brake pedal is pressed, pressurized fluid from the master cylinder assembly moves the shuttle valves to open lines 'A' and close the shuttle valve switches. Pressurized fluid then flows through the open inlet solenoid valves to operate the brakes. The closed shuttle valve switches supply a brakes on signal to the SLABS ECU. If the SLABS ECU determines that EBD is necessary, it energizes the inlet solenoid valves for the brakes of one axle. The inlet solenoid valves close to isolate the brakes from any further increase in hydraulic pressure.

ABS braking mode
When in the normal braking mode, if the SLABS ECU determines that ABS braking is necessary, it energizes the inlet and outlet solenoid valves of the related brake and starts the return pump. The inlet solenoid valve closes to isolate the brake from pressurized fluid; the outlet solenoid valve opens to release pressure from the brake into the expansion chamber and the return pump circuit. The brake releases and the wheel begins to accelerate. The SLABS ECU then operates the inlet and outlet solenoid valves to control the supply of hydraulic pressure to the brake and apply the maximum braking effort (for the available traction) without locking the wheel.

Active braking mode
When ETC or HDC are enabled, and the SLABS ECU determines that active braking is necessary, it starts the return pump. Hydraulic fluid, drawn from the reservoirs through the master cylinder, shuttle valves and lines 'B', is pressurized by the return pump and supplied to lines 'A'. The SLABS ECU then operates the inlet and outlet solenoid valves to control the supply of hydraulic pressure to the individual brakes and slow the wheel(s).

SLABS ECU
The SLABS ECU is attached to a bracket behind the front passenger glovebox. Brake related inputs are processed by the SLABS ECU, which then outputs control signals to the ABS modulator. Five electrical connectors interface the SLABS ECU with the vehicle wiring.



The SLABS ECU continually calculates vehicle speed using the wheel speed inputs from all four ABS sensors. The calculated vehicle speed is then used as a reference against which individual wheel speeds are monitored for unacceptable acceleration or deceleration. The ABS sensor inputs are also used by the SLABS ECU to detect vehicle deceleration rate, vehicle cornering rate and rough terrain.
The engaged forward gear and (on manual gearbox models) the clutch status are computed from the engine data input, the engine speed input and vehicle speed. Reverse gear status is provided by an input from the reverse lamp switch (manual gearbox models) or the BCU (automatic gearbox models). On automatic models, the BCU also provides the neutral selected input.
In addition to controlling the brake related functions, the SLABS ECU:
• Controls the operation of the self leveling suspension (SLS) system (where fitted). REAR SUSPENSION, DESCRIPTION AND OPERATION, Description.
• On V8 models, outputs a rough road signal to the ECM when traversing rough terrain.
• Outputs a vehicle speed signal.
The vehicle speed signal is output to the following systems (where fitted):
• Active Cornering Enhancement. FRONT SUSPENSION, DESCRIPTION AND OPERATION, Description - ACE.
• Air conditioning. AIR CONDITIONING, DESCRIPTION AND OPERATION, Description.
• Cruise control. ENGINE MANAGEMENT SYSTEM - Td5, DESCRIPTION AND OPERATION, Description.
ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine management.
• Engine management. ENGINE MANAGEMENT SYSTEM - Td5, DESCRIPTION AND OPERATION, Description.
ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine management.
• In-car entertainment. IN CAR ENTERTAINMENT, DESCRIPTION AND OPERATION, Description.
• Instrument pack. Dam INSTRUMENTS, DESCRIPTION AND OPERATION, Description.
ABS sensors
The ABS sensors supply the SLABS ECU with a sinusoidal speed signal from each wheel. An inductive sensor, installed in the hub bearing of each wheel, senses off a 60 tooth exciter ring integrated into the inner race of the hub bearing. Each ABS sensor has a fly-lead connecting it to the vehicle wiring.

HDC switch
The HDC switch is a latching push switch installed on the fascia, in the switch pack inboard of the steering wheel. When pushed in, the switch connects an ignition supply to the SLABS ECU to initiate HDC.

Warning indications
The SLABS ECU operates audible and visual warnings to convey brake system status.

Audible warning
A repetitive chime, at a frequency of 2 Hz, draws attention to warning lamp indications. The chime is produced on the speaker in the instrument pack.

Warning lamps

The following brake system warning lamps can be found in the instrument pack:
• A red brake graphic (all except NAS vehicles) or red BRAKE legend (NAS vehicles), to warn of low brake fluid level, hand brake on and brake control system failure affecting EBD.
• An amber ABS graphic, to warn of brake control system failure affecting the ABS function.
• An amber to graphic, to warn of brake control system failure affecting the ETC function.
• Two inclined vehicle graphics, one amber (fault) and one green (information), to indicate operating status of HDC and to warn of brake control system failure affecting the HDC function. Each warning lamp is illuminated by a separate LED. The ABS, brake and ETC warning lamps are continuously on while illuminated; the two HDC warning lamps are either continuously on or flash at a frequency of 2 Hz while illuminated.

General
The brakes consist of front and rear disc brakes operated by a diagonally split, dual circuit hydraulic system with vacuum servo power assistance. The system incorporates the following control functions as standard on all models:
• Anti-lock Brakes (ABS) , to prevent road wheels locking during brake application.
• Electronic Brake Distribution (EBD) , to control distribution of hydraulic pressure between front and rear axles. Replaces mechanical pressure limiting valve of previous systems.
• Electronic Traction Control (ETC) , to maintain even torque distribution to the road wheels.
• Hill Descent Control (HDC) , to provide controlled descent ability in off road conditions.


For normal brake operation, brake pedal movement is assisted by the brake servo assembly and transmitted to the master cylinder assembly. The master cylinder assembly converts brake pedal movement to hydraulic pressure. Primary and secondary brake pipe circuits supply the hydraulic pressure to the brakes via the ABS modulator: the primary circuit supplies the front left and rear right brakes; the secondary circuit supplies the front right and rear left brakes. Vacuum for the brake servo assembly is obtained from the engine inlet manifold (V8 models) or a vacuum pump (diesel models), through a vacuum line and non return valve. To reduce operating noise, sleeving is installed on some of the brake pipes in the engine compartment and the pipes are located in sprung pipe clips.
For all control functions, the ABS modulator regulates the hydraulic pressure to the brakes to control the speed of all four wheels, either individually or in axle pairs. Operation of the ABS modulator is controlled by the Self Leveling and Anti-lock Braking Systems (SLABS) ECU. The SLABS ECU also operates warning indications in the instrument pack to provide the driver with status information on each function.

Brake Servo Assembly
The brake servo assembly provides power assistance to reduce the pedal load when braking. If the brake servo assembly fails, the hydraulic system still functions but will require greater brake pedal effort due to the lack of vacuum assistance.

Two integral tie bolts attach the brake servo assembly to the pedal and bracket assembly on the engine bulkhead. The master cylinder assembly is attached to the forward ends of the tie bolts.

The brake servo assembly consists of a circular housing which contains two diaphragms, a central plate, a control valve assembly, input and output push rods and a filter. The input push rod is connected to the brake pedal. The output push rod locates in the primary piston of the master cylinder. A protective gaiter is installed on the control valve assembly where it extends from the rear of the housing. A non return valve, installed in a port in the front face of the housing, is connected to a vacuum line from the engine.

The control valve assembly consists of a valve body containing a valve, a piston, a valve spring and an input rod spring. The valve controls a vacuum port in the valve body. The piston controls an air inlet port between the valve and the piston. A reaction disc and a ratio disc separate the piston from the output push rod. A guide tube on the front of the valve body is attached to the front diaphragm and supported in a bush in the central plate. A return spring locates in the open end of the guide tube.

The two diaphragms and the central plate separate the interior of the housing into four sealed chambers. The chambers at the front of the diaphragms are connected together through fixed passages in the valve assembly. The chambers at the rear of the diaphragms are connected together through the interior of minor diaphragms on the tie bolts.

Brakes off
With the brake pedal released, the piston in the control valve assembly positions the valve so that the vacuum port is open and the two pairs of chambers are connected together. When the engine is running air is evacuated through the vacuum line and non return valve, creating a partial vacuum in all four chambers. When the engine stops, the non return valve closes to maintain the partial vacuum and, on V8 models, prevent fuel vapor entering the brake servo.


Brakes on
When the brake pedal is pressed, the input push rod and the piston initially move forward in the valve body. The valve body and output rod then move with the input rod, against resistance from the return spring, to transmit the brake pedal force to the master cylinder assembly.

During the initial movement of the piston, the valve, assisted by the valve spring, moves with the piston and closes the vacuum port to isolate the chambers at the rear of the diaphragms from the vacuum source. Further movement of the input push rod causes the piston to move away from the valve and open the air inlet port. This allows a restricted flow of filtered ambient air through the air inlet port, which creates a servo pressure in the chambers at the rear of the diaphragms. Force from the resultant pressure differential across the diaphragms is transmitted through the valve body to the output push rod, augmenting the pressure being applied by the brake pedal. The force produced by the diaphragms, in proportion to the input force, i.e. the boost ratio, is 5.6:1. The boost ratio remains constant, as the input force from the brake pedal increases, until the limit of assistance is reached when servo pressure is equal to ambient pressure.

Brakes held on
When the brake pedal effort is constant, opposing pressures cause the reaction disc to extrude onto the ratio disc, which moves the piston against the valve to close the air inlet port. This prevents any further increase in servo pressure and maintains a constant output force to the master cylinder assembly.

Brakes released
When the brake pedal is released, the input rod spring moves the input rod and piston rearwards within the valve body to close the air inlet port and open the vacuum port. The air from the chambers at the rear of the diaphragms is then evacuated, through the vacuum port and the chambers at the front of the diaphragms, to restore a partial vacuum in all four chambers. Simultaneously, the return spring moves the valve body, diaphragms, output rod and input rod rearwards to return them to their brakes off position.

Vacuum pump (diesel models only)

As the diesel engine air inlet system does not produce sufficient depression to operate the brake servo assembly, an engine driven vacuum pump is installed.
The vacuum pump is integrated with the engine alternator and driven by the auxiliary drive belt. The pump is a rotary vane type, lubricated and cooled by engine oil supplied through a pipe connected to the engine block and returned through a pipe connected to the engine oil sump. Air extracted from the brake servo assembly is vented into the oil sump with returning lubricating oil.

Master Cylinder Assembly




The master cylinder assembly produces hydraulic pressure to operate the brakes when the brake pedal is pressed.
The assembly is attached to the front of the brake servo assembly, and comprises a cylinder containing two pistons in tandem. The rear piston produces pressure for the primary circuit and the front piston produces pressure for the secondary circuit. A brake fluid reservoir is installed on top of the cylinder. The reservoir is internally divided to provide an independent supply of fluid to each brake circuit, and so prevent a single fluid leak from disabling both primary and secondary brake circuits. Should a failure occur in one circuit, the remaining circuit will still operate effectively, although brake pedal travel and vehicle braking distances will increase. If the fluid level in the reservoir is too low, a float operated switch in the reservoir filler cap connects an earth to the instrument pack, which illuminates the brake warning lamp.

Brakes applied
When the brake pedal is pressed, the output rod in the brake servo assembly pushes the primary piston along the cylinder bore. This produces pressure in the primary pressure chamber which, in conjunction with the primary spring, overcomes the secondary spring and simultaneously moves the secondary piston along the cylinder bore. The initial movement of the pistons, away from the piston stops, closes the primary and secondary center valves. Further movement of the pistons then pressurizes the fluid in the primary and secondary pressure chambers, and thus the brake circuits. The fluid in the chambers behind the pistons is unaffected by movement of the pistons and can flow unrestricted through the feed holes between the chambers and the reservoir.

Brakes released
When the brake pedal is released, the primary and secondary springs push the pistons back down the bore of the cylinder. The rapid movement of the pistons cause partial vacuums to form in the pressure chambers, which opens the center valves and allows fluid to circulate unrestricted between the two hydraulic circuits and the reservoir. When the pistons reach the brakes off position, the center valves are held open by the piston stops.

The ABS modulator is a 4 channel unit that controls the supply of hydraulic pressure to the brakes in response to inputs from the SLABS ECU. The modulator is attached by three mounting bushes to a bracket on the LH inner front wing, and connected to the primary and secondary hydraulic circuits downstream of the master cylinder assembly. Three electrical connectors link the ABS modulator to the vehicle wiring.

Passages within the ABS modulator, separated into primary and secondary circuits, connect to the various internal components that control the supply of hydraulic pressure to the brakes:
• Shuttle valves and non return valves control the flow through the internal circuits.
• Shuttle valve switches, connected in series to the SLABS ECU, provide a brakes on/off signal.
• A damper chamber and restrictor are included in each circuit to refine system operation.
• Inlet and outlet solenoid valves control the flow to the individual brakes.
• An expansion chamber is connected to each circuit to absorb pressure.
• A return pump is connected to both circuits to provide a pressure source. The ABS modulator has three operating modes: Normal braking, ABS braking and active braking.
Normal braking mode
When the brake pedal is pressed, pressurized fluid from the master cylinder assembly moves the shuttle valves to open lines 'A' and close the shuttle valve switches. Pressurized fluid then flows through the open inlet solenoid valves to operate the brakes. The closed shuttle valve switches supply a brakes on signal to the SLABS ECU. If the SLABS ECU determines that EBD is necessary, it energizes the inlet solenoid valves for the brakes of one axle. The inlet solenoid valves close to isolate the brakes from any further increase in hydraulic pressure.

ABS braking mode
When in the normal braking mode, if the SLABS ECU determines that ABS braking is necessary, it energizes the inlet and outlet solenoid valves of the related brake and starts the return pump. The inlet solenoid valve closes to isolate the brake from pressurized fluid; the outlet solenoid valve opens to release pressure from the brake into the expansion chamber and the return pump circuit. The brake releases and the wheel begins to accelerate. The SLABS ECU then operates the inlet and outlet solenoid valves to control the supply of hydraulic pressure to the brake and apply the maximum braking effort (for the available traction) without locking the wheel.

Active braking mode
When ETC or HDC are enabled, and the SLABS ECU determines that active braking is necessary, it starts the return pump. Hydraulic fluid, drawn from the reservoirs through the master cylinder, shuttle valves and lines 'B', is pressurized by the return pump and supplied to lines 'A'. The SLABS ECU then operates the inlet and outlet solenoid valves to control the supply of hydraulic pressure to the individual brakes and slow the wheel(s).

SLABS ECU
The SLABS ECU is attached to a bracket behind the front passenger glovebox. Brake related inputs are processed by the SLABS ECU, which then outputs control signals to the ABS modulator. Five electrical connectors interface the SLABS ECU with the vehicle wiring.


The SLABS ECU continually calculates vehicle speed using the wheel speed inputs from all four ABS sensors. The calculated vehicle speed is then used as a reference against which individual wheel speeds are monitored for unacceptable acceleration or deceleration. The ABS sensor inputs are also used by the SLABS ECU to detect vehicle deceleration rate, vehicle cornering rate and rough terrain.
The engaged forward gear and (on manual gearbox models) the clutch status are computed from the engine data input, the engine speed input and vehicle speed. Reverse gear status is provided by an input from the reverse lamp switch (manual gearbox models) or the BCU (automatic gearbox models). On automatic models, the BCU also provides the neutral selected input.
In addition to controlling the brake related functions, the SLABS ECU:
• Controls the operation of the self leveling suspension (SLS) system (where fitted). REAR SUSPENSION, DESCRIPTION AND OPERATION, Description.
• On V8 models, outputs a rough road signal to the ECM when traversing rough terrain.
• Outputs a vehicle speed signal.
The vehicle speed signal is output to the following systems (where fitted):
• Active Cornering Enhancement. FRONT SUSPENSION, DESCRIPTION AND OPERATION, Description - ACE.
• Air conditioning. AIR CONDITIONING, DESCRIPTION AND OPERATION, Description.
• Cruise control. ENGINE MANAGEMENT SYSTEM - Td5, DESCRIPTION AND OPERATION, Description.
ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine management.
• Engine management. ENGINE MANAGEMENT SYSTEM - Td5, DESCRIPTION AND OPERATION, Description.
ENGINE MANAGEMENT SYSTEM - V8, DESCRIPTION AND OPERATION, Description - engine management.
• In-car entertainment. IN CAR ENTERTAINMENT, DESCRIPTION AND OPERATION, Description.
• Instrument pack. Dam INSTRUMENTS, DESCRIPTION AND OPERATION, Description.
ABS sensors
The ABS sensors supply the SLABS ECU with a sinusoidal speed signal from each wheel. An inductive sensor, installed in the hub bearing of each wheel, senses off a 60 tooth exciter ring integrated into the inner race of the hub bearing. Each ABS sensor has a fly-lead connecting it to the vehicle wiring.

HDC switch
The HDC switch is a latching push switch installed on the fascia, in the switch pack inboard of the steering wheel. When pushed in, the switch connects an ignition supply to the SLABS ECU to initiate HDC.

Warning indications
The SLABS ECU operates audible and visual warnings to convey brake system status.

Audible warning
A repetitive chime, at a frequency of 2 Hz, draws attention to warning lamp indications. The chime is produced on the speaker in the instrument pack.


Warning lamps

The following brake system warning lamps can be found in the instrument pack:
• A red brake graphic (all except NAS vehicles) or red BRAKE legend (NAS vehicles), to warn of low brake fluid level, hand brake on and brake control system failure affecting EBD.
• An amber ABS graphic, to warn of brake control system failure affecting the ABS function.
• An amber to graphic, to warn of brake control system failure affecting the ETC function.
• Two inclined vehicle graphics, one amber (fault) and one green (information), to indicate operating status of HDC and to warn of brake control system failure affecting the HDC function. Each warning lamp is illuminated by a separate LED. The ABS, brake and ETC warning lamps are continuously on while illuminated; the two HDC warning lamps are either continuously on or flash at a frequency of 2 Hz while illuminated.