Jaguar XJ (X350). Manual — part 238

7

Brake pedal switch

8

Anti-lock Brake System (ABS)/Dynamic Stability Control (DSC) module

INTRODUCTION

The ABS modulates brake pressure on each wheel independently to maintain vehicle stability during

braking. The ABS continually monitors the rotational velocity of each wheel during driving and

determines if a tire is skidding when the brakes are applied. Only then does the ABS intervene to

modulate the brake pressure to the skidding wheel. The modulation continues until the wheel

rotates freely. The brake pressure is then restored and the modulate/restore cycle is repeated

whenever skidding is detected. This cycle occurs at a rate of several times per second.

The ABS control module is capable of detecting the following system conditions:

•

Hydraulic valve failure

•

Wheel speed sensor failure

•

ABS power relay short circuit

•

Interconnect failures to the ABS sensors, power and ground to the ABS module

•

Over/under voltage conditions

The ABS provides self-diagnostics and displays failure messages through the ABS warning indicator in

the instrument cluster. Failure of the ABS module, for whatever reason, will not compromise the

normal operation of the brake system.

The DSC system includes the:

•

anti-lock brake system

•

lateral/yaw control

•

full speed traction control

The DSC system manages the braking system to enhance the driver control of the vehicle.

The DSC system continually monitors the steering wheel angle, master cylinder brake pressure, front

and rear wheel speeds and vehicle lateral/yaw rate acceleration.

The lateral/yaw rate sensor supplies a signal to the DSC module, via a serial link, which monitors the

vehicles rate of acceleration from its central axis in a sideways direction, and also the vehicles

angular rotation around its central axis.

The driver input parameters are continually monitored by the steering wheel rotation sensor and the

hydraulic control unit master cylinder pressure sensor.

The DSC is enabled/disabled through the traction control ON/OFF switch.

Self-diagnosis of the DSC system is provided through the instrument cluster and message center.

Traction control is an additional function added to the ABS/DSC system. The vehicles driven wheels

are continually monitored for wheel spin relative to the calculated reference speed and to each

other. If wheel spin is detected, the traction control function intervenes independently of the driver,

applying brake pressure to the spinning wheel and reducing the engine drive torque supply.

Meanwhile, brake pressure is modulated by the traction control until traction is re-established.

Traction control brake actuation is diminished above 40 kph (25 mile/h). Above this speed, traction

control relies primarily on engine torque reduction.

Traction control is enabled/disabled through the traction control ON/OFF switch. When the switch is

in the OFF position, the amber traction control warning lamp solidly illuminates within the

instrument cluster message center. The traction control is automatically activated when the ignition

is switched on. Self-diagnosis of the traction control system is also provided through the instrument

cluster and message center.

The traction control brake intervention is automatically disabled whenever the brakes exceed a

temperature limit. The traction brake intervention will remain disabled until the brakes have cooled.

Hydraulic Control Modulator Brake Tube Location - Left-hand Drive

Item

Part Number

Description

1

Secondary circuit

2

Front left-hand

3

Front right-hand

4

Primary circuit

5

Rear left-hand

6

Rear right-hand

www.

Hydraulic control Modulator Brake Tube Location - Right-hand Drive

Item

Part Number

Description

1

Secondary circuit

2

Front left-hand

3

Front right-hand

4

Primary circuit

5

Rear left-hand

6

Rear right-hand

Brake Vacuum Assist (3.0L V6 and 3.5L V8 Vehicles Only)

Operation of Brake Vacuum Assist is possible at the start of an ignition cycle when the engine is cold

and low vacuum levels are generated by the engine. Its operation will result in vibrating pedal and

some modulator noise. This may appear to be similar to unexpected ABS (anti-lock brake system)

function, at lower than expected speed or light braking effort. As the engine warms up, Brake

Vacuum Assist operation should become less frequent, though it can be active in other circumstances

where vacuum levels are lower than required; for example, at higher altitudes or during frequent,

heavy braking.

Additionally, noise levels during Brake Vacuum Assist may be variable, with initial system activity

louder than normal activity. In some circumstances initial activity louder than normal may be

interpreted as a 'thump' noise, particularly if there is no significant Brake Vacuum Assist functionality

that immediately follows.

In these cases, this system behaviour is not unexpected, and should not be a cause for fault

investigation.

Diagnosis and testing

Anti-Lock Control - Stability Assist - VIN
Range: G00442->G45703

Principle of operation

The anti-lock control - stability assist system includes the:

•

anti-lock brake system (ABS)

•

yaw/acceleration control

•

emergency brake assist

•

traction control

Anti-lock Brake System (ABS)

The anti-lock brake system (ABS) modulates brake pressure on each wheel independently to

maintain vehicle stability during braking. The ABS continually monitors the rotational velocity of each

wheel anytime the ignition switch is in the run position and determines if a tire is skidding when the

brakes are applied. Only then does the ABS intervene to modulate the brake pressure to the skidding

wheel. The modulation continues until the wheel rotates freely. The brake pressure is then restored

and the modulate/restore cycle is repeated whenever skidding is detected. This cycle occurs at a rate

of several times per second.

The ABS module is capable of detecting the following system conditions:

•

hydraulic valve failure

•

wheel speed sensor failure

•

ABS power relay short circuit

•

interconnect failures to the ABS sensors, power and ground to the ABS module

•

over/under voltage conditions

The ABS provides self-diagnostics and displays failure messages via the ABS indicator in the

instrument cluster. Failure of the ABS module, for whatever reason, will not compromise the normal

operation of the brake system.

Traction Control

Traction control is an additional function added to the anti-lock control - stability assist system. The

vehicles driven wheels are continually monitored for wheel spin relative to the calculated reference

speed and to each other. If wheel spin is detected, the traction control function intervenes, applying

brake pressure to the slipping wheel and reducing the engine drive torque supply. Meanwhile, brake

pressure is modulated by the traction control until traction is re-established. Traction control brake

actuation is diminished above 40 km/h (25 mph). Above this speed traction control relies primarily on

engine torque reduction.

The traction control brake intervention is automatically disabled whenever the brakes exceed a

www.