L322 Range Rover System Description and Operation
DRIVING AIDS
86-10-16 DESCRIPTION AND OPERATION
Wheel Position
The wheel position phase takes from 3 to 15 minutes. The signals from each tyre sensor are received by all four
antennas, so by monitoring the strength of the signals received by each antenna the TPM ECU determines the
position of the individual tyre sensors and assigns them a wheel position, including, by inference, the spare wheel tyre
sensor (where fitted).
The TPM ECU confirms the wheel positions from the tyre temperatures. When the vehicle is driven the temperature
of the road wheels changes, while the temperature of the spare wheel remains relatively constant. When it detects a
4
°
C (7.2
°
F) change in temperature, the TPM ECU confirms a road wheel position for the related tyre sensor. When
it detects a temperature increase of less than 4
°
C (7.2
°
F) then, provided only one wheel has a temperature increase
of less than 4
°
C (7.2
°
F), the TPM ECU confirms the related tyre sensor in the spare wheel position. The fifth wheel
can also be confirmed in the spare wheel position by default, after four road wheel positions have been confirmed.
After successful assignment and confirmation of the wheel positions, the TPM ECU checks the nominal tyre pressures
to ensure they are within the following limits:
l
The nominal tyre pressures must not be less than 1.7 bar (24.65 lbf/in
2
)
l
The nominal tyre pressures of wheels on the same axle must be within 0.4 bar (6 lbf/in
2
) of each other.
If the nominal pressures are within the limits, the TPM ECU stores them in memory in place of the previous nominal
pressures. Initialisation is successfully completed and the TPM ECU continues to monitor the current tyre pressures
against the new nominal pressures.
If a new nominal pressure is outside the limits, the TPM ECU aborts the initialisation process and reverts to the
previous nominal pressures for pressure monitoring. The TPM ECU also signals the instrument pack to display the
CHECK TYRE PRESSURE message on the message centre for 40 seconds. While the ignition is on the message is
repeated at 1 minute intervals until a valid initialisation is performed.
Occasionally the system may have difficulty assigning and confirming wheel positions, e.g. due to signal interference,
if a spare wheel is masked by luggage, etc. If the TPM ECU cannot successfully complete the wheel position phase,
it discontinues the initialisation process and reverts to the previous nominal pressures for pressure monitoring. At the
start of the next ignition cycle, the TPM ECU also signals the instrument pack to display the CHECK TYRE
PRESSURE message.
Wheel Confirmation
At the beginning of each drive cycle, if the system is not being initialised the TPM ECU retrieves the stored wheel data
from memory and checks it against the current identification and position of the tyre sensors to determine if the tyre
sensor arrangement has changed without being initialised.
If it detects the same tyre sensors installed in different positions, the TPM ECU assigns and confirms the tyre sensors
to their new wheel positions and retains their existing nominal pressures. At the start of the next ignition cycle, the
TPM ECU signals the instrument pack to display the CHECK TYRE PRESSURE message as a reminder to check
that the tyre pressures are correct for their wheel positions and to initialise the system.
If it detects a new tyre sensor on the vehicle, the TPM ECU signals the instrument pack to activate the TYRE
CONTROL INACTIVE warning while it learns the identity, wheel position and nominal pressure of the new sensor in
a similar manner to the initialisation process. Once the learning process is completed, the TPM ECU signals the
instrument pack to de-activate the TYRE CONTROL INACTIVE warning.
If the confirmation process cannot be completed within 30 minutes, the TPM ECU signals the instrument pack to
activate the TYRE CONTROL INACTIVE warning for the remainder of the drive cycle.
If the TPM ECU detects additional tyre sensors during confirmation, e.g. if additional spare wheels fitted with tyre
sensors are being carried in the vehicle, it disables the system, stores a 'too many wheel sensors' message and
signals the instrument pack to activate the TYRE CONTROL INACTIVE warning.
Pressure Monitoring
The TPM ECU continuously compares the current tyre pressures against the nominal pressures stored in memory.
From each tyre's current pressure and temperature, the TPM ECU calculates the theoretical pressure at 20
°
C (68
°
F) and compares the result with the tyre's nominal pressure. If the current pressure varies from the nominal pressure
by more than the preset limits, the TPM ECU signals the instrument pack to produce a caution or warning as
appropriate.