System Description -2
Brake booster/ABS modulator unit
Mounted in the same position as a conventional brake master cylinder/servo unit, the brake booster/ABS modulator contains the following components: fluid reservoir, power valve, master cylinder, isolating valve, ABS control valves and servo cylinders. It also contains the ETC solenoid control valves
NOTE: The brake booster/ABS modulator unit is not a serviceable item, if internal failure occurs a new unit must be fitted. The fluid reservoir and its seals may be changed in the event of damage.
WARNING: Extreme care must be taken when changing reservoir seals to avoid ingress of debris.
Fluid reservoir - 1.
Mounted on top of the unit, the plastic reservoir is subdivided internally to provide separate capacity for brake fluid used in the hydrostatic and power circuits. A central tube incorporates a filter. A built in fluid level warning switch and a finer filter for the power circuit fluid are also incorporated. The fluid level warning switch is closed when there is sufficient fluid in reservoir.
On manual vehicles, the reservoir also supplies fluid to the clutch system.
Master cylinder - 2.
Operation of the master cylinder displaces a volume of brake fluid into the servo cylinders and increases fluid pressure. Piston movement inside the master cylinder will also activate the power valve.
Power valve - 3.
The power valve is an extension of the master cylinder, it controls fluid pressure in the power circuit in direct proportion to pressure in the master cylinder. The power valve is of spool valve design.
Isolating valve - 4.
The isolating valve consists of two solenoid valves controlling fluid inlet and outlet. Their function is to disconnect the master cylinder from the servo cylinders and to connect the servo cylinders to the reservoir return during ABS function.
ABS solenoid control valves, 8 off- 5.
Each pair, comprising inlet and outlet solenoid valves, control ABS braking to each wheel. In response to signals from the ECU, the valves decrease, hold or increase brake pressure according to the need to retain wheel rotation and obtain optimum braking. The solenoid valves are designed to respond rapidly to ECU signals.
Servo cylinders, 2 off- 6.
Servo cylinders have five functions:
1. To provide combined energy from both hydrostatic and power circuit to brake calipers.
2. To provide 'brake feel' at the brake pedal.
3. To provide hydrostatic (master cylinder) braking through the servo cylinders to calipers in the event of no power circuit pressure to servo cylinders.
4. To provide braking from the power circuit and from hydrostatic fluid remaining in servo cylinder, in event of no hydrostatic circuit pressure from master cylinder.
5. To provide ABS control to the front calipers in response to pressure modulations in the power circuit.
ETC control valves - up to 99MY - 7 & 8
The ETC control valves are optional on vehicles up to 99MY. The ETC inlet solenoid valve (7) is normally closed and the ETC isolating solenoid valve (8) is normally open when ETC operation is not required.
When ETC operation is required, the inlet solenoid valve opens allowing fluid from the power circuit to flow to the rear ABS solenoid control valves. Simultaneously, the ETC isolating solenoid valve closes, isolating the connection to the PCRV. The ABS ECU energizes the applicable ABS solenoid valve to pressurize the applicable rear wheel brake.
ETC control valves - from 99MY- 7 & 8
The ETC control valves are standard on vehicles from 99MY. The ETC inlet solenoid valve (7) is normally closed and the ETC isolating solenoid valve (8) is normally open when ETC operation is not required.
When ETC operation is required, the inlet solenoid valve opens allowing fluid from the power circuit to flow to the power valve. The power valve is actuated by the pressure and opens to allow fluid from the power circuit to flow directly to the front ABS solenoid control valves and to the rear solenoid control valves via the PCRV. The ETC isolating solenoid valve closes isolating the return flow from each ABS solenoid control valve. The ABS ECU energizes the applicable ABS solenoid valve(s) to pressurize the applicable front and/or rear wheel brake.
ABS power unit
The ABS power unit consists of an electrically driven pump, a pressure switch and an accumulator.
The pressure switch incorporates three electro-mechanical switches: one for the pump, another, at a different pressure setting, to illuminate the pressure warning lamp. The latter switch plus a third switch inform the ECU of low pressure and that ABS function should cease while pressure remains low. The pump also incorporates a non-return valve and a pressure relief valve to protect the system.
NOTE: The pump and pressure switch are not serviceable, if failure occurs a new unit must be fitted.
The diaphragm type accumulator is fitted to the power unit. The accumulator is precharged with nitrogen at up to 80 bar. Its function is to store hydraulic energy ready for the next brake application.
NOTE: Accumulator replacement is possible if failure occurs. Correct disposal of old accumulators is essential. See Repair.
Pressure Conscious Reducing Valve (PCRV)
The PCRV is located adjacent to the brake booster/ABS modulator unit. It is connected between the power valve and ABS solenoid valves for the rear axle. Its function is to limit brake pressure to rear axle.
NOTE: The PCRV is not a serviceable item, if failure occurs a new unit must be fitted.
Brake calipers - front and rear
NOTE: To identify separate hydraulic circuits, they are referred to as HYDROSTATIC and POWER circuits.
Power circuit - Consists of rear calipers and servo cylinders, supplied by direct hydraulic power from the power valve.
Hydrostatic circuit - Consists of servo cylinders supplied by master cylinder pressure. The front calipers are supplied with direct hydraulic energy from the servo cylinders, comprising a combination of master cylinder pressure and direct hydraulic power.
ABS Electronic Control Unit - ECU
ABS/ETC operation is controlled by the ECU. The ECU is attached to a bracket, which in turn is attached to the bulkhead. A closing plate beneath the passenger side fascia provides access to the ECU.
The ECU is connected to the ABS harness by a 35 pin connector on up to 99MY vehicles and by 9, 15 and 18 pin connectors on vehicles from 99MY.
When system faults are detected by the ECU, warning lamps in the instrument pack can be illuminated for ABS, ETC and braking system faults. Certain faults are also displayed in the instrument pack message center. Refer to Operation - Warning lamps for lamp and message center operation.
The ABS ECU generates a digital road speed signal from the average speed of the four wheels. The ABS ECU passes the road speed signal to the BCM. The BCM outputs the road speed signal to the following interfaces:
^ Engine Control Module (ECM)
^ Cruise control ECU (V8 only)
^ Instrument pack
^ Air Temperature Control (ATC) ECU
^ In-Car Entertainment (ICE)
^ Electronic Air Suspension (EAS) ECU
^ Electronic Automatic Transmission (EAT) ECU.
The ABS ECU also outputs a rough road signal to the ECM on V8 engine vehicles only. The digital rough road signal is generated from the difference in rotational speed of each wheel.
The ECU is a non-serviceable item, it must be replaced if failure occurs
ABS ECU connector pin details - up to 99MY
ABS ECU connector face view
35 win connector No. C116
ABS ECU connector pin details- From 99MY
Relays and fuses - Up to 99MY
The ABS electrical system has two relays and three fuses, located in the engine compartment fuse box.
^ Relay 2 (yellow) - ABS valve relay.
^ Relay 15 (green) - Ignition relay - ABS power.
^ Relay 17 (black) - ABS pump relay. Note that this relay is unique to the ABS system.
^ Fuse Maxi 3 (40 Amp) - ABS pump relay.
^ Fuse 24 (5 Amp) - ABS ECU - Ignition supply.
^ Fuse 27 (30 Amp) - ABS ECU - Battery supply.
Relays and fuses - From 99MY
The ABS electrical system has two relays and three fuses, located in the engine compartment fusebox.
^ Relay 15 (green) - Ignition relay - ABS power.
^ Relay 17 (black) - ABS pump relay. Note that this relay is unique to the ABS system.
^ Fuse Maxi 3 (40 Amp) - ABS pump relay.
^ Fuse 24 (5 Amp) - ABS ECU - Ignition supply.
^ Fuse 38 (30 Amp) - ABS ECU - Battery supply.
Sensors, exciter rings - 4 off
A sensor is mounted at each wheel, sensing a 60 tooth exciter ring. When the vehicle is in motion the inductive sensors send signals to the ECU.
The front exciter ring is fitted adjacent to the constant velocity joint in each front hub. The rear exciter ring is inside the axle adjacent to the wheel bearing assembly.
NOTE: Road speed information from the ECU is transmitted to the Body electrical Control Module (BCM) to drive the speedometer and all systems requiring speed information, except the transfer box ECU.
Brake calipers
Lucas Colette type calipers are used all round. The front disc brake calipers each house two pistons, hydraulic pressure is supplied by a combination of power and hydrostatic circuit. The rear disc brake calipers each house one piston, hydraulic pressure is supplied by the power circuit via a Pressure Conscious Reducing Valve (PCRV).
The operation of both front and rear calipers is in principle the same. The Colette type caliper consists of two main components, a carrier and a hydraulic body assembly. The carrier is bolted to the hub assembly. The hydraulic body slides on two greased guide pins housed in the carrier. The guide pins are sealed by the dust covers to avoid unequal sliding loads caused by dirt or corrosion.
When the foot brake is applied hydraulic pressure pushes the piston and, with it, the inboard pad on to the disc. The hydraulic body reacts and slides on the guide pins to bring the outboard pad into contact with the disc. The clamping force on both sides of the disc is then equal.
When hydraulic pressure is released, the piston seal retracts the piston a small amount. This allows the moving parts to relax sufficiently for the brake pads to remain in close proximity to the disc ready for the next brake application.
Brake caliper assembly
The hand operated parking brake acts on a brake drum at the rear of the transfer gearbox and is completely independent of the hydraulic circuits.
NOTE: Illustration shows a front, two piston, caliper. Rear calipers are of similar construction with a single piston.
Brake pipe layout - Left hand drive
Brake pipe layout - Right hand drive
ANTI-LOCK BRAKE SYSTEM - OPERATION
Warning lights
Brake fluid pressure/level and parking brake warning lamp - (red)
The warning lamp situated in instrument binnacle indicates insufficient pressure in system and/or low fluid level and/or park brake applied. The warning lamp will illuminate, for 3 seconds when ignition is switched ON as part of initial bulb check, and continuously when parking brake is applied. If the pressure in hydraulic system is lower than the cut-in pressure for the warning lamp, the lamp will illuminate. When the lamp is on hydraulic pump will be heard running.
NOTE: If the lamp remains illuminated after the bulb check AND releasing the park brake, DO NOT drive the vehicle until the lamp extinguishes.
WARNING: IF THE LAMP ILLUMINATES WHILE THE VEHICLE IS IN MOTION, INVESTIGATE FAULT IMMEDIATELY. BRAKING WILL BE AVAILABLE AFTER LOSS OF PRESSURE, BUT GREATER FORCE AND TRAVEL WILL BE REQUIRED AT THE PEDAL TO SLOW THE VEHICLE.
ABS warning lamp - (yellow)
WARNING: Power assisted braking is not available if ignition is switched off. An increase in effort at brake pedal will be required to apply brakes.
The ABS warning lamp situated in instrument binnacle indicates a failure in ABS system.
The warning lamp will illuminate for 1 second when ignition is switched ON, it will briefly extinguish and will illuminate again. This indicates that the system self monitoring check was successful, and system performs correctly.
If it does not extinguish and illuminate again a system fault has occurred.
The warning lamp will extinguish when vehicle speed exceeds 7 km/h (5 mph).
If lamp remains on or subsequently illuminates with ignition ON a fault in ABS system is indicated. The self monitoring procedure is repeated frequently while ignition is ON. If a fault is detected during self monitoring, the lamp will illuminate indicating that one or more wheels are not under ABS control.
WARNING: Reduced ABS control is possible with ABS warning lamp illuminated depending on severity and type of fault. If both ABS and brake failure warning lamps are illuminated, loss of system pressure or hydraulic pump failure is indicated. STOP VEHICLE AND IMMEDIATELY INVESTIGATE THE FAULT.
Traction control warning lamp - (amber)
The Traction Control warning lamp situated in instrument pack informs the driver that traction control is active. The warning lamp will illuminate when the ignition is switched ON, and the ABS and ETC systems have completed their self checks, the 'TC' lamp will illuminate for 3 seconds. This indicates that the ETC system is operative, and also performs the bulb check.
When traction control is active the lamp will illuminate for a minimum of 2 seconds, a single audible chime will sound and the message center will display 'TRACTION'. The message and lamp will be extinguished when ETC has stopped working.
On later models, the 'TRACTION' message is not displayed in the message center. The driver is informed of ETC operation by the 'TC' warning lamp and the single audible chime.
If a fault disables TC, the TC lamp will illuminate and the message 'TRACTION FAILURE' will be displayed. A single audible chime will sound on the first occurrence of the message.
If the system is over used and there is a risk of components overheating, the system will shut itself down. The TC lamp will flash for 10 seconds minimum, a single audible chime will sound and the message 'TRACTION OVERHEAT' will be displayed. Traction control will be available after components have cooled down.
NOTE: Traction control only operates below 50 km/h (30 mph) on models up to 99MY and below 100 km/h (62.5 mph) on models from 99MY.
Warning lamp functionality
Diagnostics
While the ignition is in position 11, the ABS ECU monitors the system for faults. Diagnostic information and system function monitoring can be accessed by connecting Test Book to the vehicle diagnostic connector in the passenger footwell, near the center console.
After detecting a fault, the ABS ECU will select a suitable default strategy which will retain, if possible, some operational ABS capability. If ABS is not active, conventional braking will be remain available. Fault codes are stored in the ECU's memory for current and historic faults. The stored fault codes can be accessed, read and then cleared when the fault is rectified.
Driving the vehicle
WARNING: On surfaces which are soft and deep, for example deep powdery snow, sand or gravel, braking distance may be greater than with non ABS braking. In these conditions wheel lock and the build up of snow or gravel under wheels may be an aid to shorter stopping distance. However it is still an advantage to maintain the stability and maneuverability available with ABS control.
1. Switch on ignition, system will automatically carry out self test function. This will be felt as a slight movement in brake pedal and a short, rapid series of clicks indicating that solenoid valves have been checked.
2. Observe warning lights, check parking brake/fluid warning light extinguishes after initial bulb check or when parking brake is released, indicating that power assistance is available. Note time taken to pressurize system is up to 40 seconds.
3. Start vehicle and drive away, at 7 km/h (5 mph) the ABS warning light must be extinguished.
4. In road conditions where surface friction is sufficient to slow or stop the vehicle without wheel lock, ABS does not operate.
5. In an emergency braking situation, if one or more wheels begin to slow rapidly in relation to vehicle speed, ABS will detect wheel locking tendency and will regulate brake pressure to maintain wheel rotation.
6. ABS operation will be felt as a vibration through pedal, at same time solenoid cycling will be heard.
NOTE: Constant pressure on foot pedal whilst ABS is operating is more effective than cadence braking. Do not pump brake pedal, this may reduce ABS efficiency and increase stopping distance.
7. Downward travel of pedal will also feel hard at point at which ABS operates. Little further pedal travel is possible at this point, BUT, force on the pedal can be varied to influence braking force while ABS retains control.
Brake application with partial failure
WARNING: IF A FAULT DEVELOPS IN THE BRAKE SYSTEM IT IS ESSENTIAL THAT IT IS INVESTIGATED IMMEDIATELY.
NOTE: If, during braking, a drastically reduced resistance is detected at pedal and braking effectiveness is very much reduced, failure of the non-powered (master cylinder) portion of system is indicated. When this occurs, DO NOT PUMP BRAKE PEDAL. Push the pedal through free movement to obtain braking effort from the power circuit. It is essential that brake pedal travel is not obstructed by items such as extra footwell mats.
8. When power assistance is not available, ABS braking is not operative. Both warning lights are illuminated. Braking effort is available from master cylinder only. This results in longer pedal travel and greater pedal effort required to decelerate vehicle.
WARNING: FOOT PRESSURE ON THE PEDAL, USING MASTER CYLINDER ONLY, WILL NOT ACHIEVE THE SAME DEGREE OF BRAKING AS IS AVAILABLE FROM POWER ASSISTANCE.
9. If master cylinder fails, i.e. there is insufficient fluid in master cylinder to create pressure, braking to all four wheels is retained and ABS remains operative. The red warning light will be illuminated if cause of the master cylinder failure is a fluid leak and level in fluid reservoir is low enough to actuate fluid level switch.
WARNING: LONGER PEDAL TRAVEL IS REQUIRED, BUT POWER ASSISTED BRAKING IS AVAILABLE AT REDUCED EFFICIENCY.
10. If brake failure occurs due to a fractured brake pipe between a servo cylinder and a wheel, there may be no pressure in the master cylinder. The fluid warning light will illuminate when level in fluid reservoir is low enough to actuate fluid level switch. Master cylinder and power valve will operate as for master cylinder failure, BUT, fluid from power circuit will push all moving parts in servo cylinder associated with failure to limit of travel. No pressurized fluid passes to the front brake caliper served by the affected servo cylinder, but pistons in rear calipers will be supplied with direct pressure from power valve. The front caliper served by the other servo cylinder retain braking as fluid from master cylinder is retained in servo cylinder not associated with the leakage.
WARNING: BRAKE PEDAL TRAVEL WILL BE GREATER AND EXTRA PEDAL EFFORT WILL BE REQUIRED, ACCOMPANIED BY THE VEHICLE PULLING TO ONE SIDE.