Jaguar XJ (X350). Manual — part 87

Tire Low Pressure Sensor

The tire pressure monitoring system uses ‘active’ tire low pressure sensors which are mounted on

each wheel, inside the tire cavity. The sensor is retained in position by the valve attachment to the

wheel. The tire low pressure sensors transmit their Radio Frequency (RF) signals at either 315 MHz or

433 MHz dependent on market requirements.

The tire low pressure sensor periodically measure the pressure and temperature of the air inside the

tire. Pressure and temperature measurements are transmitted periodically to the external RF

antenna on the vehicle.

The tire low pressure sensors are self-contained units which have no electrical connections into or

out of the tire low pressure sensor.

The care points detailed in 'Tire Changing' must be followed to avoid damage to the tire low pressure

sensor. If the tire low pressure sensor is removed, the nut, valve core, cap, seal and washer must also

be replaced and the tire low pressure sensor tightened to the correct torque value. It is also

recommended that the nut, valve core, cap, seal and washer are replaced at every tire change.

The RF transmission from the tire low pressure sensor contains a unique identification code in its

transmission data, so that the tire pressure monitoring system module can identify the tire on the

vehicle. If the tire low pressure sensor is replaced on a road wheel, the new sensor identification will

be learnt when the vehicle is first driven at a speed of more than 20 km/h (12.5 miles/h) for 15

minutes. If a new tire low pressure sensor is fitted to the spare wheel, the identification for that tire

low pressure sensor must be programmed into the tire pressure monitoring system module using a

Jaguar approved diagnostic tool or that wheel will not be monitored. The code is provided on a label

with the complete wheel and tire assembly when new and is also printed on the casing of each tire

low pressure sensor.

In order to conserve battery power, the tire pressure monitoring system module uses different

transmission rates when the wheel is stationary or moving. The wheel speed required to change

between the stationary and moving transmission rates is approximately 20 kph (12.5 mile/h).

Antenna

The antennas are located near the front of the front wheel arches, and the rear of the rear wheel

arches. The tire pressure monitoring system has four antennas. Each antenna has a connector which

connects with the body wiring harness.

The antenna is a passive, Low Frequency (LF) transmitter. Each antenna is controlled by the tire

pressure monitoring system module and provides an auto-location feature to identify tire positions

on the vehicle.

The tire pressure monitoring system module energizes each antenna in turn using LF drivers. The

corresponding tire low pressure sensor detects the resulting LF transmission and modifies the mode

status within the RF transmission. This data is received by the tire pressure monitoring system

module through the external RF antenna. The tire pressure monitoring system module can then

determine which sensor is transmitting and its location on the vehicle.

External Antenna

The tire pressure monitoring system external antenna is located at the rear of the vehicle and is

mounted between the spare wheel well and rear subframe.

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The unit receives tire pressure, temperature and acceleration readings from each tire and interfaces

with the tire pressure monitoring system module. The tire pressure monitoring system module then

transmits the appropriate messages to the instrument cluster.

The unit also receives further information from each tire pressure sensor concerning wheel

identification, mode status and the condition of the tire pressure sensor battery.

Instrument Cluster Indications

Item

Part Number

Description

1

Low tire pressure warning indicator

2

Secondary amber warning indicator

3

Message center

Warnings are displayed by the low tire pressure warning indicator, the secondary amber warning

indicator and a text message displayed in the message center.

The warning indicators are driven by controller area network (CAN) messages from the tire pressure

monitoring system module. The warning indicators are illuminated by the instrument cluster

software for three seconds when the ignition is switched to position II for a bulb check.

Note: If the vehicle is not fitted with the tire pressure monitoring system, the warning indicators will

not illuminate at any time.

System Operation

The tire low pressure sensor transmits by RF (315 MHz or 433 MHz depending on market) signal.

These signals contains data which corresponds to tire low pressure sensor identification, tire

pressure, tire temperature, acceleration and tire low pressure sensor mode.

Each time the vehicle is driven, the tire pressure monitoring system module activates each LF

antenna in turn. The corresponding tire low pressure sensor detects the LF signal and responds by

modifying the mode status within the RF transmission.

The system enters 'parking mode' after the vehicle speed has been less than 20 km/h (12.5 miles/h)

for 12 minutes. In parking mode the tire low pressure sensors transmit a coded signal to the tire

pressure monitoring system module once every 13 hours. If the tire pressure decreases by more than

0.06 bar (1 lbf/in²) the tire low pressure sensor will transmit more often as pressure is lost.

The spare tire sensor transmits a signal every 13 hours in the same manner as the road wheels when

in parking mode. If the tire pressure decreases by more than 0.06 bar (1 lbf/in²) the tire low pressure

sensor will transmit more often as pressure is lost.

As each wheel responds to the LF signal from the tire pressure monitoring system module, it is

assigned a position on the vehicle and is monitored for the remainder of that drive cycle in that

position.

When the vehicle has been parked for more than 15 minutes and then driven at a speed of more

than 20 km/h (12.5 miles/h), the antennas fire in turn for 6 seconds on all except North American

specification vehicles or for 18 seconds on North American specification only vehicles in the following

order:

•

Front left

•

Six second pause (for the tire pressure monitoring system module to detect a response from
the tire low pressure sensor)

•

Front right

•

Six second pause

•

Rear right

•

Six second pause

•

Rear left

•

Six second pause

Each tire low pressure sensor responds in turn so the tire pressure monitoring system module can

establish the tire low pressure sensor positions at the start of the drive cycle. This process is repeated

up to three times but less if the tire low pressure sensor positions are already known in the tire

pressure monitoring system module. This process is known as 'Auto Location' and takes three to four

minutes on all except North American specification vehicles and seven to eight minutes on North

American specification vehicles to complete. During this period the tire low pressure sensors

transmit at regular intervals, once every 5 seconds on all except North American specification

vehicles and once every 15 seconds on North American specification vehicles. For the remainder of

the drive cycle the tire low pressure sensors transmit once every 60 seconds or if a change in tire

pressure is sensed until the vehicle stops and the tire pressure monitoring system returns to parking

mode.

Once the wheel position is established, the antennas stop firing and do not fire again until the vehicle

has been parked for more than 15 minutes. The signal transmissions from each tire low pressure

sensor continue at one minute intervals whilst the vehicle is being driven. This transmission is to

monitor the tire pressure. The warning occurs at 25% deflation and comprises of message center

amber secondary warning light, the low tire pressure warning indicator and an appropriate message

displayed in the instrument cluster message center. The message center will also display additional

information about the position of the affected wheel(s).

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