ABS JAGUAR XJ6 1994 2.G User Guide

SECTION CONTENTS
Subsection Tit/e SRO Page
i to iv ............ Preliminary Pages .................................................................... i
12.1 ............. Anti-Lock Braking System (ABS) General Description ................................... 12.1
12.1.2.
........... Anti-lock Braking/ Traction Contd Operation ........................................ 12.3
12.1.3
............ Anti-lock Braking Operation ........................................................ 12.4
12.1.4
............ Actuation Components ............................................................. 12.5
12.1.5
............ ABSComponents ................................................................. 12.6
12.1.6
............ Calipers ........................................................................\
. 12.7
12.1.7
............ Parking Brake .................................................................... 12.9
12.1.8
............ Wheel Speed Sensors ............................................................. 12.11
12.1.9
............ Hydraulic Operation - ABS CM .................................................... 12.12
12.2
............. Fault Diagnosis and Testing ........................................................ 12.16
12.4
............. Brake System Bleeding ............................................................ 12.19
12.1.10
.......... Hydraulic Operation - ABS /TC CM ................................................. 12.14
12.3
............. Brake Fluid Level Check .......................................................... 12.18
12.4.1
............ System Bleeding - General Instructions .............................................. 12.19
12.4.2.
........... System Bleeding After Brake Fluid Renewal .......................................... 12.19
12.4.3
............ System Bleeding After Tandem Master Cylinder Renewal ............................... 12.19
12.4.4.
........... System Bleeding Afier Hydraulic Control Module Renewal ............................. 12.20
12.4.5.
........... Bleeding After Renewal of Caliper .................................................. 12.20
12.5
............. General Fitting Instructions ........................................................ 12.2 1
12.5.1 ............ General Fitting Instructions, Brake Fluid ............................................. 12.2 1
12.5.2. ........... General Fitting Instructions, Hoses .................................................. 12.2 1
12.5.3 ............ General Fitting Instructions, Pipes ................................................... 12.2 1
12.6 ............. Rear Wheel Speedsensor- Renew ............................... 70.60.04 ......... 12.22
12.7
............. Hydraulic Control Module- Renew ............................... 70.60.18/ 19 ..... 12.23
12.8
............. Pressure Conscious Reducing Valves .............................. 70.60.21 ......... 12.25
12.9
............. ABS/TCCM - Renew .......................................... 70.60.02/20 ..... 12.26
X300 VSM i Issue 1 August 1994

12.1 ANTI-LOCK BRAKING SYSTEM (ASS), GENERAL DESCRIPTION
The anti-lock braking system (ABS) components are combined with a hydraulic booster and tandem master cylinder (TMC) to provide a two-circuit braking system. The anti-lock braking system comprises the following components:
0 Four inductive wheel speed sensors, hub end mounted
0 ABS warning light
0 Hydraulic module.
The hydraulic module consists of an electric motor driven pump,
two low pressure accumulators, valve block and an
ABS electronic control module.
m: Electronic control modules for vehicles without traction control are designated ABS CM. Control modules for
vehicles with traction control are designated ABS /TC CM.
The valve block houses solenoid operated valves which are activated by voltage signals from the control module. The
signals are generated using wheel speed information received from the wheel speed sensors.
For vehicles without traction control the valves operate on three circuits, two front and one rear, as necessary to pre
- vent wheel locking during braking. Brake pressure is modulated individually at thefront wheels and collectively at the
rear. Rear wheel control operates on a 'select low' principle i.e. locking in either wheel is sensed, and controlled brake
pressure is applied to both wheels.
For vehicles with traction control the valves operate on four circuits. During ABS control the rear wheel are controlled
on a 'select low' principle (as above), but during traction control operation the rear wheels are controlled individually.
0
1yQfB: Functional and diagnostic information for the ABS CM and the ABS/TC CM is contained in the Electrical Diag-
nostic Manual (EDM), Section 12.
ABS Warning lamp / Traction Control Warning lamp /Fluid level Indicator
The ABS and traction control warning lamps, mounted in the instrument panel, indicate a fault in the ABS or traction
control. These systems are inhibited or disabled when the lamps are lit, although conventional braking is unaffected.
When the ignition is switched on, an ABS self test is initiated. During this test, the ABS and traction control warning
lamps are
lit for approximately 1.7 seconds and then extinguish. A fault is indicated if the warning lamps remain lit or
come on whilst the vehicle is being driven.
W: The ABS self test is masked by the 5 second lamp test initiated when the ignition is switched on.
The fluid level indicator lamp, mounted in the instrument panel, is
lit when the brake fluid falls below the minimum
mark on the brake fluid reservoir.
ABS / Traction Control - Inhibit / Disable
Faults conditions are detected by the ABS/TC CM which disables the ABS and traction control until the fault is rectified.
The ABS and traction control warning lights on the instrument pack remains lit whilst a fault exists. The system will
be disabled when the following conditions occur:
0
0 Valve failure
0 Sensor failure
0 Main driver failure (internal ABS /TC CM fault)
0 Redundancy error (internal ABS JTC CM fault)
0 Overvoltage J undervoltage
0 Pump motor failure.
0 Throttle valve actuator motor failure (traction control vehicles only).
0 Throttle valve actuator potentiometer failure (traction control warning light only).
X300 VSM 1 Issue 1 August 1994

The input frequency from each wheel speed sensor signal is translated by the ABS I TC CM, into a comparable wheel
speed. The ABS / TC CM continually monitors the system. False wheel speed information, such as sudden speed
changes in excess of 20 km / h or excessive speeds, are detected as a 'sensor malfunction'. The ABS / TC CM reacts
to fault conditions in the following ways:
Inhibit- ABS/traction control is inhibited until the sensed speed returns to within an acceptable limit, whereupon ABS
/traction control is restored. Conventional braking is unaffected. Depending on vehicle speed the ABS/traction control
warning lights may come on.
DisaMe - ABS /traction control is Disabled (switched off) and the ABS /traction control warning lights come on. The
system will not be restored until the engine is switched off and restarted orthe fault has been rectified. Afterthe system
has been disabled, the warning lamps remain on until the vehicle has reached a speed of 20 km/ h during thefirst igni- tion cycle after fault rectification.
Full diagnostic information for the ABS /TC
CM is given in the Electrical Diagnostic Manual (EDM), Section 12.
Issue 1 August 1994 2 X300 VSM

Brakes (a)
12.1.2. Anti-lock Braking / Traction Control Operation
The rear wheels are controlled collectively on a 'select-low' principle during ABS operation. During traction control,
separate circuits allow individual control of the rear wheels. To facilitate this the valve block has four outlet ports.
The
ABS/TC CM is integrated with the valve block. The pump, motor, valve block and control module are supplied as
a unit and are non-sewiceable. Faulty units must be renewed as a whole.
Both front and rear brakes on
all vehicles are fitted with single piston caliper assemblies. Ventilated brake rotors, with
provision for parking brake shoes at the rear, are fitted all round.
0
Issue 1 August 1994 X300 VSM 3
1. Vacuum booster 9. Pressure conscious reduction valve 2. Vacuum hose 10. Ventilated brake rotor 3. Tandem master cylinder 11. Single piston caliper 4. Primary brake circuit 12. %way brake pipe connector
5. Secondary brake circuit 13. Wheel speed sensor
6. Hydraulic pump / motor unit 14. ABS warning lamp 7. Valve block 15. Brake fluid level warning lamp
8. ABS/TCCM
Fig. 1 ABS / Traction Control System
The vacuum booster (see Fig.
1) is mounted on the brake pedal box and secured by three bolts. Brake pedal force is
increased by the vacuum booster which activates the Tandem Master Cylinder (TMC) intermediate piston. Brake fluid
is supplied to the pump inlet ports on two separate circuits. The primary circuit supplies the front brakes whilst the
secondary circuit supplies the rear brakes.

Pressure conscious reduction valves (PCRVs) are fitted between the outlet of the valve block and the rear brake circuit
to optimize. The valves are fitted to prevent over braking due to the increased size of the rear brake calipers which are
required for traction control. Up to a threshold of 15 bar, brake pressure to the front and rear brakes is equal. Above
15 bar the PCRVs reduce pressure to the rear brakes to provide a closer balance between front and rear brakes and
optimize road adhesion.
Wheel speed sensors are fitted to all wheels to transmit wheel speed information to the control module. The module
uses this information to modulate brake pressure during anti
-lock braking or traction control.
12.1.3. Anti-lock Braking Operation
170 287
1. Vacuum booster 9. Pressure conscious reduction valve
2. Vacuum hose 10. Ventilated brake rotor
3. Tandem master cylinder 11. Single piston caliper
4. Primary brake circuit 12.
%way brake pipe connector
5. Secondary brake circuit 13. Wheel speed sensor
6. Hydraulic pump I motor unit 14. ABS warning lamp 7. Valve block 15. Brake fluid level warning lamp
8. ABSICM
Fig. 1 Brake System (non-Traction Control)
The rear brakes (see Fig. 1) are controlled collectively on a
'select-low' principle. Under ABS braking conditions, equal
brake pressure is applied to both rear calipers, although only one wheel may have a tendency to lock.
The valve block has three outlet
ports, Brake fluid volume is supplied equally to the rear brakes via the %way brake
pipe connector.
Issue 1 August 1994 4 X300 VSM

12.1.5. ABS Components
Hydraulic Module
The hydraulic module is located under the bonnet adjacent
to the engine compartment firewall. It is secured within a steel mounting bracket at three securing points. All elec- tronic and power connections are made through one cable
loom connect ion.
The hydraulic pump
(1 Fig. 1) is a reciprocating two-circuit pump in which one brake circuit is assigned to each pump
circuit. The pump supplies adequate pressure and volume
supply to the brake circuits under anti
-lock braking condi- tions. The pump is driven by and electric motor (2 Fig. 1). The
pump housing incorporates two low pressure accumulators
and damping chambers for each brake circuit.
A modulator valve block
(3 Fig. 1) incorporates the ABS CM or ABS / TC CM (4 Fig. 1). Vehicles with traction control are
fitted with a throttle position actuator (5 Fig. I), which is an
electrical device controlled by the ABS 1 TC CM.
Valve blocks on vehicles without traction control comprise
six solenoid valves, three normally open (NO) inlet valves
and three normally closed
(NC) outlet valves. These valve
blocks have three outlet ports. Valve blocks on vehicles with
traction control comprise nine solenoid valves, four
NO inlet valves,four NC outlet valves and one special isolating valve.
Fig. 2 shows a hydraulic module for vehicles with traction
control. The valve block (2 Fig. 2) has four outlet ports (Indi- vidual control of the driven wheels).
A BS CM, A BS / TC CM
The ABS CM or ABS TCI CM locates beneath the modulator
valve block and is secured by
two screws. The CM houses
the solenoids which operate the inlet and outletvalves of the
modulator valve block. When fitted, the valve stems locate
in the
CM mounted solenoids. There is no electrical connec- tion between the CM and the modulator valve block. Fig. 3 shows an ABS TC 1 CM having nine solenoids.
The
CM functions include the following:
0 Providing control signals for the operation of ABS
and traction control solenoid valves
0 Calculating wheel speed from voltage signals trans- mitted by the wheel speed sensors
0 Monitoring of all electrical components
0 On Board Diagnostics (OBD): storage of possible fail- ures in a non-volatile memory.
The signals from the four wheel speed sensors are indepen
- dently processed by the ABS CM or ABSITC CM, calculating
numerical values which correspond directly to the wheel
speed. These values are converted into control signals for
pressure modulation during ABS control.
The ABS and traction control
are continuously monitored,
whilst the ignition is on,for possiblefaults and interruptions.
If a fault is detected, the module deactivates the ABS and
indicates this by lighting the ABS warning lamp. In a fault
condition, conventional braking is unaffected. The module
stores fault codes in a non
-volatile memory which can be
read via the OBD link.
U: For electrical diagnostic information on the ABS I traction control systems, refer to EDM, Section 12. Fia.
1
Fia. 2
Fin. 3 I
J70286
Issue 1 August 1994 X300 VSM

12.1.9
The TMC primary circuit (item 1) applies brake pressure to the front brakes. Individual control of the front wheels is
provided by solenoid valves, Valves (items
15 and 18) control the front left brake circuit (item 21). Valves (items 16and 19) control the front right brake circuit (item 22). The TMC secondary circuit (item 2) applies brake pressure to the rear
brake circuit (item 20) via valves (items 14 and 17), on a 'select low' principle.
Hydraulic Operation - A BS CM
8
I I + I
I t 1
'0281
1. TMC 1 (primary circuit) 9. Low pressure accumulator 17. Outlet valve NC 2. TMC 2 (secondary circuit 10. Electric pump motor 18. Outlet valve NC
3. Tandem master cylinder 11. Two circuit hydraulic pump 19. Outlet valve NC 4. Vacuum booster 12. Damping chamber 20. Rear brake circuit 5. Central valve 13. Valve block 21. Front brake circuit (left)
6. Fluid reservoir 14. Inlet valve NO 22. Front brake circuit (right) 7. Fluid level indicator 15. Inlet valve NO 8. Pump motor unit 16. Inlet valve NO
Fig.
1
Should the ABS be initiated by a locking tendency of any wheel during braking, the pump unit (item 8) is started and
the appropriate NO inlet valve (item 14, 15 or 16) closes in response to signals from the control module. This action
prevents further increase of brake pressure by blocking the supply of brake fluid from the TMC (item 3). If excessive
deceleration continues, the appropriate NC outlet valves (item 17,18 or 19) opens, releasing brake pressure to the low
pressure accumulators (item 9) until the wheel accelerates again.
Issue 1 August 1994 12 X300 VSM

From the low pressure accumulators,volume is pumped back into theTMC, forcing the brake pedal back. To optimize the friction coefficient between tire and road, brake pressure is increased in small steps by closing the outlet valve and
opening the inlet valve and re-charging brake pressure.
During the pressure build
up phase, the volume required for replenishment is supplied by the TMC and additionally
by the pump from the low pressure accumulators. Since the delivered flow is generally greater than volume flow
drained from the brake circuits, the low pressure accumulators serve as intermediate accumulators to compensate for
temporary volume flow peaks.
The TMC piston positions, and therefore the brake pedal, vary with the fluid displacement in the brake caliper. As con
-
trolled pressure in the brake caliper decreases and increases during ABS, the brake pedal 'cycles', informing the driver
that controlled braking is in progress.
Actuation of the brake pedal, causes the central valve (item
5) in the TMC to close. This action prevents damage to the
TMC piston seals.
At the end of a brake application, volume is restored to the TMC, at
low pressure from the fluid reservoir (item 6).
Issue 1 August 1994 X300 VSM 13

12.1.1 0 Hydrauric Operation - ABS 1 TC CM
ABS/TC CM hydraulic modules incorporate inlet valves (items 16 and 17) and outlet valves (items 20 and 21) for each
driven wheel. This enables individual pressure modulation to the rear brakes under wheel spin conditions, i.e. traction
control.
Increased wheel spin of
a driven wheel under acceleration causes the NO isolation valve (item 14) to be closed and the
pump (item 10) to be switched on. This in response to signals from the control module.
Closing of the isolation valve blocks delivery of the pump to the secondary circuit (item
2) of the TMC. The pump now
draws fluid from the reservoir via the open hydraulically operated inlet valve (item 13). Increased pressure is now avail-
able at the inlet valves (items 16 and 17) for actuating the rear brakes, thus decreasing the tendency of wheel spin.
The hydraulic inlet valve (item
13) switches when traction control is initiated to change the suction connection
of the pump from the accumulators (item 9) to the fluid reservoir (item 6) via the TMC.
1. TMC 1 (primary circuit)
8
I 1-
I
10. Electric DumD motor 19. Inlet valve NO
170 280
2. TMC 2 (secondary circuit) 11. Two-cirh hydraulic pump 20. Outlet valve NC
3. Tandem master cylinder 12. Damping chamber 21. Outlet valve NC
4. Vacuum booster 13. Hydraulic inlet valve 22. Outlet valve NC
5. Central valve 14. Isolation valve NO 23. Outlet valve NC
6. Fluid reservoir 15. Relief valve 7. Fluid level indicator 16. Inlet valve NO 8. Motor pump unit 17. Inlet valve NO 9. Low pressure accumulator 18. Inlet valve NO
Fig.
1 24.
Rear
brake circuit (left) 25. Rear brake circuit (right) 26. Front brake circuit (left) 27. Front brake circuit (right) ~
Issue 1 August 1994 14 X300 VSM

Brakes
The pressure at the inlet valves corresponds to the opening pressure of the relief valve (item 15) incorporated in the
isolation valve. Excess brake fluid is drained to the suction side of the pump via the relief valve and returns either to
the TMC secondary circuit and on to the
fluid reservoir, or is directly drawn on by the pump.
As soon as the spinning wheel has been braked down into the normal range of wheel spin, the NO valves (items
16 or 17) close to prevent any further increase in brake pressure. Depending upon the acceleration of the wheel, the NC
valve (item
20 or 21) may open to decrease thesecondary circuit brake pressure. NCvalves (item 17 or 18) may remain
closed in orderto achieve a brake pressure holding phase. If the pressure in the secondarycircuit needs to be increased
again, the NC valve closes again (if open) and the NO valve opens, diverting the necessary volume flow. This control
action, keeps the wheel in the range of optimum slip until the spinning tendency ceases.
The NO isolation valve
(14) remains closed throughout the traction control cycle.
An actuation of the brake, sensed by the control module, causes the traction control mode to be terminated and the
isolation valve (item
14) to be opened. The TMC pressure simultaneously closes the hydraulic inlet valve (item 13) so that the pump can no longer draw fluid from it. The ABS / TC CM now operates in normal ABS mode.
m: When traction control is initiated, speed control is deactivated (if in operation) and requires re-setting after
the traction control mode has terminated. Gear shift is inhibited on automatic transmission vehicles; no down- shifts are allowed and upshifts occur at 4800 RPM.
X300 VSM 15 Issue 1 August 1994