Description
Wheels and Tires
NOTE:
A = Hardwired; B = K-Line Bus; F = RF Transmission; D = High Speed CAN (controller area network) Bus; W = LF Transmission
System Operation
Each time the vehicle is driven, the CJB (central junction box) transmits a Low Frequency (LF) (125 KHz) signal to each initiator in turn. This is received by the tire pressure sensor which transmits a Radio Frequency (RF) (315 or 433 MHz depending on market) signal to the RF receiver. This signal contains coded data which corresponds to sensor identification, air pressure, air temperature and acceleration data. This signal is communicated to the CJB (central junction box) via a K-Line Bus.
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 CJB (central junction box) once every 13 hours. If the tire pressure decreases by more than 1 lbf/in2 (0.6 bar), the sensor will transmit more often if pressure is being lost.
As each wheel responds to the LF signal from the CJB (central junction box), 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 12.5 mph (20 km/h), the initiators fire in turn for 18 seconds in the following order:
- Front left
- 6 second pause (for the system to detect a response from the tire pressure sensor)
- Front right
- 6 second pause
- Rear right
- 6 second pause
- Rear left
- 6 second pause.
Each tire pressure sensor responds in turn so the CJB (central junction box) can establish the sensor positions at the start of the drive cycle. This process is repeated up to three times but less if the sensor positions are already known in the CJB (central junction box). The process is known as 'Auto Location' and takes up 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.
Once the wheel position is established, the initiators stop firing a signal and do not fire again until the vehicle has been parked for more than 15 minutes. The signal transmissions from each wheel sensor continue at 1 minute intervals whilst the vehicle is being driven. This transmission is to monitor the tire pressure.
At 25% deflation the amber warning indicator in the instrument cluster is illuminated and an appropriate message displayed in the message center.
Tire Location
Because of the requirement for different pressure targets and thresholds for the front and rear tires, the CJB (central junction box) can identify the location of the tires on the vehicle, and assign a received tire pressure sensor identification to a specific position on the vehicle (i.e. FL (front left), FR (front right), RL (rear left) or RR (rear right)).
Tire location is performed automatically by the CJB (central junction box) using an auto-location function. This function requires no manual intervention by the driver. The CJB (central junction box) 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 traveling at less than 12 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 mph (20 km/h) for 15 minutes. If the vehicle speed reduces to below 12 mph (20 km/h), the learn process timer is suspended until the vehicle speed increases to more than 12 mph (20 km/h), after which time the timer is resumed. If the vehicle speed remains below 12 mph (20 km/h) for more than 15 minutes, the timer is set to zero and process starts again.
The CJB (central junction box) 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, i.e. the CJB (central junction box) can reject identifications from tire pressure sensors that do not belong to the vehicle
- the spare tire and one of the tires in use on the vehicle have exchanged position on the vehicle.
If the tire pressure sensors fitted to the running wheels (not the spare) are changed, the CJB (central junction box) can learn the new sensor identifications automatically. The learn function requires no manual intervention by the driver.
Spare Tire Identification
Depending on the vehicle specification, the spare tire may or may not be fitted with a tire pressure sensor.
NOTE:
Tire pressure sensors cannot be fitted to steel space saver spare wheels.
If the spare tire is being monitored and the driver replaces a flat 'running' tire with the spare tire, the CJB (central junction box) will not continually warn the driver that the original flat tire (now in the spare position) is flat. This prevents distraction of the driver by constant pressure warnings being issued. The driver is reminded by a message displayed for 20 seconds at each ignition on cycle that the spare tire is flat.
RF Receiver
The RF receiver is mounted on headliner next to overhead console and connects to the vehicle harness via a fly lead.
The RF receiver receives transmissions from each of the tire pressure sensors via an internal antenna. This information is then communicated to the CJB (central junction box) via a dedicated LIN (local interconnect network) bus.
Initiator
The initiators are located at the front of the front wheel arches and at the rear of the rear wheel arches and are secured with two scrivets. The TPMS has four initiators and each has a connector which connects with the body harness.
The initiator is a passive, Low Frequency (LF) transmitter. Each initiator provides an auto-location feature to identify tire positions on the vehicle and transmit that data to the CJB (central junction box).
The CJB (central junction box) energizes each initiator in turn using LF drivers. The corresponding tire pressure sensor detects the resulting LF transmission and responds by initiating an RF transmission of its data. This data is received by the RF receiver and communicated to the CJB (central junction box) via a K-Line Bus. The CJB (central junction box) can then determine which sensor is transmitting and its location on the vehicle.
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 either 315 MHz or 433 MHz dependent on market requirements.
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 CJB (central junction box) can identify the tire on the vehicle. If the sensor is replaced on a 'running' wheel, the new sensor identification will be learnt when the vehicle is first driven at a speed of more than 12.5 mph (20 km/h) for 15 minutes. If a new sensor is fitted to the spare wheel, the identification for that sensor must be programmed into the CJB (central junction box) 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
The warning indications to the driver are common on all vehicles fitted with TPMS. Warnings are conveyed by an amber LED (light emitting diode) warning indicator and a text message displayed in the message center.
The warning indicator and message center are driven by CAN (controller area network) messages from the CJB (central junction box). The warning indicator is illuminated by the cluster software for 3 seconds when the vehicle is in power mode 6 for a bulb check.
For additional information, refer to Information and Message Center Overview
Controller Area Network (CAN)
The CJB (central junction box) sends and receives a number of digital messages via CAN (controller area network). 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.
Transmitted Messages
The CJB (central junction box) transmits the messages shown in the following table.
Diagnostics
The CJB (central junction box) has a diagnostic connection via the Medium Speed CAN (controller area network) to enable system status and faults to be retrieved using a Land Rover approved diagnostic system.
Additionally, an on-board diagnostic routine within the CJB (central junction box) 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' is the tire position on the vehicle, e.g. FL (front left), FR (front right), RL (rear left) or RR (rear right).
If more than one sensor fails or the CJB (central junction box) develops a fault, the amber warning indicator will be illuminated. A message 'Tire Monitoring System Fault' will be displayed in the message center in addition to the amber warning indicator. 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 voltage becomes low, the sensor transmits a message to the CJB (central junction box). The CJB (central junction box) stores the low battery condition as a fault flag in its memory with no other visual warnings displayed. If the battery fails, the sensor will stop transmitting and the CJB (central junction box) will transmit a message to display 'FL Tire Not Monitored' for example in the message center. The dealer should interrogate the CJB (central junction box) for the fault flag using a Land Rover approved diagnostic system to determine the cause of the message. If the battery has failed, the sensor must be replaced and the stored fault flags removed using a Land Rover approved diagnostic system. The CJB (central junction box) will learn the identification of the new sensor when the vehicle is driven. If the replaced sensor is
fitted to the spare wheel (if fitted), its identification must be manually programmed into the CJB (central junction box) using a Land Rover approved diagnostic system or by using it as a 'running' wheel for 15 minutes at more than 12.5 mph (20 km/h), then replacing it to the spare wheel position.