Jaguar XJ (X350). Manual — part 236

Description and operation

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

Item

Part Number

Description

1

—

Engine control module

2

—

Instrument cluster

3

—

Steering wheel angle sensor

4

—

Wheel speed sensor - rear

5

—

Yaw/lateral rate sensor

6

—

Wheel speed sensor - front

7

—

Brake pedal switch

8

—

Brake pedal travel sensor

9

—

Brake master cylinder primary pressure transducer

10

—

ABS/DSC hydraulic control modulator

11

—

Master cylinder active booster solenoid

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.

The Dynamic Stability Control (DSC) system includes the:

•

anti-lock brake system.

•

yaw/lateral 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, vehicle yaw and lateral rate acceleration.

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

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

angular rotation around it's central axis.

The driver input parameters are continually monitored via the brake master cylinder dynamic

stability control sensor, the brake pedal travel sensor and the steering wheel angle sensor.

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

Self-diagnosis of the DSC system is provided via the instrument cluster message centre.

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 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.

Traction control is enabled/disabled via 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 centre. The traction control is automatically activated when the ignition is switched

on. Self-diagnosis of the traction control system is also provided via the instrument cluster message

centre.

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,

irrespective of ignition switch position or ignition switch cycling.

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.

Anti-Lock Control - Stability Assist - VIN
Range: G45704->G99999

Item

Part

Number

Description

1

—

Engine control module (ECM)

2

—

Instrument cluster and message centre

3

—

Steering wheel rotation sensor

4

—

Wheel speed sensor - rear

5

—

Lateral/yaw rate sensor

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