L322 Range Rover System Description and Operation
DRIVING AIDS
86-10-12 DESCRIPTION AND OPERATION
Description
General
The Tyre Pressure Monitoring (TPM) system continuously monitors tyre pressures so long as vehicle battery power
is available. If a low tyre pressure is detected, the system alerts the driver via the message centre when the ignition
is on. The system monitors the tyre pressure of each road wheel and the full size spare wheel. The tyre pressure of
a space saver spare wheel is not monitored.
The TPM system consists of the following components:
l
A reset switch
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A tyre sensor in each monitored wheel
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An antenna in each wheelarch
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An ECU.
The tyre sensors measure the air pressure and temperature in the tyres and transmit the readings in radio signals at
a frequency of 433 MHz. The radio signals are received by the antennas and transferred to the TPM ECU, which
compares the information from the tyre sensors with nominal pressures stored in memory, and alerts the driver if a
tyre pressure decreases from the nominal pressure by more than the permitted limit.
The reset switch is used to initialise the TPM ECU. During initialisation the TPM ECU adopts the current tyre pressures
as the nominal pressures.
TPM Reset Switch
The TPM reset switch is a non latching push switch installed on the centre console below the A/C control panel. While
pressed, the reset switch connects a ground to the TPM ECU.
Tyre Sensor
A tyre sensor is installed on the wheel rim of each monitored wheel, and connected to the tyre inflation valve. The tyre
inflation valve and a Torx bolt secure the tyre sensor to the wheel.
The tyre sensor incorporates a pressure sensor, temperature sensor, signal processor, radio transmitter and a non
serviceable 3.6 V battery. Nominal service life of the battery is seven years. Battery status can be checked using
TestBook/T4.
The electronics of replacement tyre sensors are inactive until they have been subjected to a pressure of 1.5 bar (21.75
lbf/in
2
), i.e. installed on the wheel and the tyre inflated. To conserve power in service, the signal processor adopts
different operating modes depending on the prevailing conditions:
l
Normal operating mode, for stable or slow changes of pressure, when the sensing rate is every 3.4 seconds and
transmission rate approximately once every 55 seconds
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Emergency operating mode, adopted if the pressure decreases more than 0.2 bar (3 lbf/in
2
) in 30 seconds, when
both the sensing and transmission rates are once every 0.85 second. Reverts to normal operating mode after
218 seconds
l
Deactivated mode, for temperatures in excess of 120
°
C (248
°
F) (making sensor readings and transmission
unreliable), when sensing and transmission electronics are deactivated and the TYRE CONTROL INACTIVE
warning is displayed. The electronics are re-activated when the temperature decreases to 110
°
C (230
°
F) for
218 seconds.
Each transmission from a tyre sensor contains:
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A synchronisation byte
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Pressure reading
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Temperature reading
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Identification number
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Remaining life of the battery, in months
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Status information.