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Range Rover 2. Electrical Manual - part 26

IGNITION AND SHIFT INTERLOCK

CIRCUIT DIAGRAM

P125a
Engine Compart-
ment Fuse Box

C172

C234

K191
Ignition Key Lock
Solenoid

C234

20 A

From VIN 370859

F 29

C204

C104

C202
C102

C109
C609

C1-3

ANTI-LOCK BRAKE SYSTEM

CIRCUIT OPERATION

CIRCUIT OPERATION

The Anti–Lock Brake System prevents wheel lockup
during braking. This enables the driver to maintain
vehicle stability and ‘steerability’ while braking.

The Electronic Traction Control System aids traction
when a rear wheel spins or loses traction. The
system works by applying the brake to the spinning
rear wheel. The braking action allows more torque to
be transferred and applied to the non–spinning rear
wheel.

Anti–Lock Brake System ECU (Z108)

The Anti–Lock Brake System ECU (Z108) is a
computer that controls ABS system operation by
consistently monitoring the vehicle’s 4 wheel speeds
when the ignition is in position II. If an impending
wheel lock up is detected during this monitoring, the
Anti–Lock Brake ECU (Z108) will apply voltage to
the various inlet and outlet valve solenoids contained
in the ABS Booster Unit (Z103). Operation of the
solenoid valves regulates the pressure applied to
each wheel brake calliper and therefore prevents
wheel lock–up.

Electronic Traction Control (ETC) is an extension to
the Anti–Lock Brake System ECU. In addition to
monitoring the rear wheel speeds for lockup, the
Anti–Lock Brake System ECU also monitors wheel
speed for traction control. When rear wheel slip is
detected (one wheel spinning faster than the other),
the Anti–Lock System ECU will apply the brake to
the spinning wheel, causing additional torque to be
applied to the non–spinning wheel.

The Anti–Lock Brake System ECU applies the brake
by operating various inlet and outlet solenoid valves
in the ABS Booster.

The ETC warning light will be on for up to 60
seconds while the system is active, and the
message TRACTION is displayed. After 60 seconds
of ETC operation, the ETC warning light will begin to
flash to inform the driver that the system has been
shut down to allow the brakes to cool. Also the
message TRACTION OVERHEAT is displayed.

If the ETC warning light stays on continuously for
more than 60 seconds, a fault in the system is
indicated. The message TRACTION FAILURE is
also displayed.

The Anti–Lock Brake System ECU (Z108) also has
diagnostic capabilities that allow it to detect faults
that may impair the system’s efficiency. If a fault

occurs, the ECU informs the operator of a problem
by illuminating the ABS or the ETC warning light.
The ECU also illuminates the warning light when the
ignition is first placed in position II. The ABS warning
light will remain illuminated until the ECU completes
a self check of the system. When the ECU sees all
wheels reach a speed of 7 km/h (5 mph), the self
check is completed and the ABS warning light turns
off. If a fault is detected during the self check, the
ABS or the ETC warning light will remain on and a
fault code will be stored in memory to aid in servicing
the system. When an ABS fault has been detected,
the message ABS FAULT may also display.

The fault code can be retrieved using a diagnostic
tester.

ANTI-LOCK BRAKE SYSTEM

CIRCUIT OPERATION

ABS Booster Unit (Z103)

The ABS Booster Unit (Z103) contains 2 isolation
solenoid valves and 4 pairs of solenoid control
valves which are grounded through the harness.
When the ETC is fitted, the booster unit also
contains an additional 2 solenoid valves. The pairs of
solenoid control valves each include a fluid pressure
inlet and outlet valves that control ABS braking to
one wheel.

The Anti–Lock Brake System ECU (Z108) operates
these valves by applying battery voltage to them.
The valves are designed to decrease, hold or
increase pressure to retain wheel rotation and
optimum braking.

The 2 isolation valves consist of 2 solenoid valves
that control fluid inlet and outlet. Their function is to
disconnect or isolate the master cylinder from the
servo cylinder and to connect the servo cylinder to
the reservoir return during ABS functions.

Wheel Speed Sensors (X137, X140, X158, X161)

A wheel speed sensor is located at each wheel. The
speed sensors generate an AC voltage signal as a
toothed ring rotates past the stationary sensor
pickup. The Anti–Lock Brake System ECU (Z108)
calculates the wheel speed by measuring the
frequency of the AC voltage signal generated by the
sensors.

ABS Hydraulic Pump (M102)

The hydraulic boost for the system is provided by the
ABS Hydraulic Pump (M102), which is controlled by
the ABS Pump Relay (K102) and the ABS Pressure
Switch Unit (Z104).

The Pressure Switch unit incorporates three
electro– mechanical switches. The first operates the
pump, two more illuminate the low pressure
condition and signal that ABS and ETC functions
should be curtailed. The Hydraulic Pump includes a
hydraulic accumulator and non–return valve, as well
as a pressure relief valve to protect the system.

When low pressure occurs in the brake system, a
switch in the pressure switch unit closes to ground
the coil of the pump relay. The pump relay now
energizes and applies battery voltage from the fuse
to the hydraulic pump through the closed relay
contacts. The hydraulic pump runs to increase
pressure in the hydraulic accumulator. When
sufficient pressure is developed in the system, the
pressure switch opens to de–energize the pump
relay and to turn off the hydraulic pump.

ABS Warning Lamp

The Anti–Lock Brake System ECU (Z108) sends
signals to the BeCM which then controls the
illumination of the ABS warning lamp. The BeCM
also controls the display of the system messages.

Solenoid Valve Relay

This is energized by the ABS ECU and sends
voltage back to the part of the same ECU which
controls the solenoid valves in the booster. When the
ABS ECU detects a fault that requires a complete
system shutdown, the relay is de–energized.

ANTI–LOCK BRAKE SYSTEM

CIRCUIT DIAGRAM

Z108
Anti–Lock Brake
System ECU

C116R

RL2

[2]

S114

E167

See Ground Dis-
tribution

C172

P125a
Engine Compart-
ment Fuse Box

[2]

A.B.S.
Power Relay

F 27

30 A

F 24

5 A

C173

C176

S118

See Fuse Details

S115

E167

See Ground Dis-
tribution

E148

C114

C116R

C112

C116L

LHD

See Ground Dis-
tribution

RHD

C116L

C176

C116L

C116R

Z108
Anti–Lock Brake
System ECU

Z238
Body Electrical
Control Module
(BECM)

S103

RHD

LHD

LHD
RHD

C507

C506B

C106B

Z132
Engine Control
Module (ECM)

NAS

C116R LHD

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