Land Rover Discovery: Wheels and Tires - Description

TIRE LOCATION

Because of the requirement for different pressure targets and thresholds for the front and rear tires, the Tire Pressure Monitoring System (TPMS) can identify the location of the tires on the vehicle, and assign received tire pressure sensor identification to a specific position on the vehicle. For example: front left, front right, rear left or rear right.

Tire location is performed automatically by the TPMS using an auto-location function. This function requires no manual intervention by the driver. The TPMS can automatically learn the position of tires on the vehicle if the tire pressure sensors or their positions are changed on the vehicle.

The tire-learn and location process is ready to commence when the vehicle has been stationary or is travelling at less than 12.5 mph (20 km/h) for 15 minutes. This is known as 'parking mode'. The learn/locate process requires the vehicle to be driven at speeds of more than 12.5 mph (20 km/h) for 15 minutes. If the vehicle speed reduces to below 12.5 mph (20 km/h), the learn process timer is suspended until the vehicle speed increases to more than 12.5 mph (20 km/h), after which time the timer is resumed. If the vehicle speed remains below 12.5 mph (20 km/h) for more than 15 minutes, the timer is set to zero and process starts again.

The TPMS can automatically detect, under all operating conditions, the following:

• One or more tire pressure sensors have been replaced.
• One or more tire pressure sensor identifications are missing.
• One or more 'alien' identifications are being received; the TPMS will reject these signals.
• Identifications from tire pressure sensors that do not belong to the vehicle.
• One of the tires in use on the vehicle have exchanged position on the vehicle.
• One or more incompatible tire pressure sensors have been fitted.

If the tire pressure sensors fitted to the running wheels are changed, the TPMS can learn the new sensor identifications automatically. The learn function requires no manual intervention by the driver.

NOTES:

• The TPMS tire valve should be serviced using the suitable service kit, each time the tire is dismounted, to ensure an air tight seal.

  Attention should be made to the detail of fitting this kit.

• Care must be taken when removing and refitting tires to ensure that the tire pressure sensor is not damaged.

TIRE PRESSURE MONITOR (TPM) MODULE

The Radio Frequency (RF) receiver is integrated into the Tire Pressure Monitor (TPM) module, which is mounted on headliner next to overhead console and connects to the vehicle harness via a four pin plug.

The TPM module, receives transmissions from each of the tire pressure sensors via an internal antenna in each of the sensors. This information is then decoded and analyzed and any required warnings along with current tire pressure information is communicated on the High Speed (HS) Controller Area Network (CAN).

TIRE PRESSURE SENSOR

The TPMS system uses 'active' tire 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 structure. The sensors transmit their RF signals at 433 MHz.

The sensors periodically measure the pressure and temperature of the air inside the tire plus the centripetal acceleration acting on the sensor. These measurements are transmitted periodically to the RF receiver located behind the overhead console.

The tire pressure sensors are self-contained units which have no electrical connections into or out of the sensor.

The care points detailed in the 'Tires' section of this chapter must be followed to avoid damage to the sensor. If the sensor is replaced, the nut, seal and washer must also be replaced and the sensor tightened to the correct torque value as given in the Service Repair manual.

The RF transmission from the sensor contains a unique identification code in its transmission data, so that the TPMS can identify the tire on the vehicle. If the sensor is replaced on a 'running' wheel, the identification for that sensor must be programmed into the TPM module using a Land Rover approved diagnostic system 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 sensor.

In order to conserve battery power, the tire sensor 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 very low to allow for the requirement for slow off-road driving.

INSTRUMENT CLUSTER INDICATIONS

1. Message center
2. Amber warning indicator

The warning indications to the driver are common on all vehicles fitted with TPMS. Warnings are conveyed by an amber Light Emitting Diode (LED ) warning indicator and a text message displayed in the message center.

The warning indicator and message center are driven by CAN messages from the TPM module. The warning indicator is illuminated by the cluster software continuously when the tire pressure is low and will flash for 75 seconds in a case of a failure.

For additional information.

For additional information, refer to: Information and Message Center (413- 08 Information and Message Center, Description and Operation).

CONTROLLER AREA NETWORK (CAN)

The TPM module sends and receives a number of digital messages via the CAN bus. The received messages are used for the operation of the TPMS.

The transmitted messages comprise of TPMS status and requests to the instrument cluster to illuminate warnings indicators and/or display messages in the message center.

The TPM module transmits the messages shown in the following table:

DIAGNOSTICS

The TPM module has a diagnostic connection via the CAN bus to enable system status and faults to be retrieved using a Land Rover approved diagnostic system.

Additionally, an on-board diagnostic routine within the TPM module constantly monitors the system and alerts the driver to system faults by illuminating the amber warning indicator and/or displaying a message in the instrument cluster message center.

FAULT DETECTION

If a sensor fails, the amber warning indicator in the instrument cluster will be illuminated. A message 'XX Tire Not Monitored' will be displayed in the message center in addition to the amber warning indicator.

NOTE:

'XX' denotes the tire position on the vehicle:

FL (front left)

FR (front right)

RL (rear left)

RR (rear right).

If more than one sensor fails or the TPMS develops a fault, the amber warning indicator will be illuminated and a message 'Tire Monitoring System Fault' will be displayed in the message center. This fault could also be caused if RF interference near the vehicle affects the system signal reception. When the interference has ceased, the fault will be automatically cancelled and the TPMS will operate normally.

If a tire pressure sensor battery fails, the sensor will stop transmitting and the TPMS will transmit a message to display 'FL Tire Not Monitored' for example in the message center. The dealer should interrogate the TPMS using a Land Rover approved diagnostic system to determine the cause of the message. If the sensor has failed, the sensor must be replaced and the stored fault flags removed using a Land Rover approved diagnostic system.

OPERATION

Each time the vehicle is driven, the TPMS learns the location of the four wheel-mounted sensors:

• FL (front left)
• FR (front right)
• RL (rear left)
• RR (rear right) by combining Radio Frequency (RF) transmissions with data from the ABS module.

NOTE:

An ABS fault will not directly cause the TPMS to stop operating, however if an ABS fault persists then a TPMS warning may also be displayed in the instrument cluster.

The system enters 'parking mode' after the vehicle speed has been less than 12.5 mph (20 km/h) for 15 minutes. In parking mode the tire pressure sensors transmit a coded signal to the TPM module once every 13 hours. If the tire pressure decreases by more than 7kPa (1lb PSI; 0.07bar), the sensor will transmit more often indicating tire pressure is being lost.

The process of locating the sensors is known as 'Auto Location' and takes 7 to 8 minutes to complete. During this period the tire sensors transmit at regular intervals, once every 15 seconds. For the remainder of the drive cycle the tire sensors transmit once every 60 seconds or if a change in tire pressure is sensed until the vehicle stops and the system returns to parking mode.

At 25% (or 20% for EU market) deflation the amber warning indicator in the instrument cluster is illuminated and an appropriate message displayed in the message center.

CONTROL DIAGRAM

A = Hardwired; AN = High speed CAN (Controller Area Network) Powertrain bus; F = RF Transmission.

1. Tire Pressure Monitor (TPM) module
2. Instrument Cluster (IC)
3. Ground wire
4. Power supply
5. Tire Pressure Sensor - left front
6. Tire Pressure Sensor - right front
7. Tire Pressure Sensor - left rear
8. Tire Pressure Sensor - right rear

Wheels and Tires - OverviewWheels and Tires / Diagnosis and Testing

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