Tire Pressure Monitoring System (TPMS)
TIRE PRESSURE MONITORING SYSTEM (TPMS)Tire Pressure Monitoring System - Component Location
The purpose of the Tire Pressure Monitoring System (TPMS) is to assist the driver in maintaining the vehicle's tire pressures at the optimum level in order to:
^ improve fuel consumption
^ maintain ride and handling characteristics
^ reduce the risk of rapid tire deflation - which may be caused by under inflated tires
^ comply with legislation in relevant markets.
The TPMS measures the pressure in each of the tires on the vehicle (including the spare, if required) and issues warnings to the driver if any of the pressures deviate from defined tolerances.
NOTE: During a 'blow out' a very rapid reduction in pressure is experienced. The system is not intended to warn the driver of a 'blow out', since it is not possible to give the driver sufficient warning that such an event is occurring, due to its short duration. The design of the TPMS is to assist the driver in keeping the tires at the correct pressure, which will tend to reduce the likelihood of a tire 'blow out' occurring.
NOTE: TPMS is inhibited when the vehicle is in Delivery mode. For more details on Delivery mode refer to the PDI manual.
A single TPMS hardware configuration is used. TPMS status information is relayed to the driver with a message displayed in the instrument cluster message center and a warning indicator LED (light emitting diode).
TPMS Module
The TPMS module is mounted on a bracket adjacent the auxiliary junction box. The module is retained in position with two plastic locknuts. The three connectors of the module point towards the floor of the vehicle.
The TPMS module's main function is to detect the following:
^ the tire pressure is below the recommended low tolerance value - under inflated tire
^ the location of the tire on the vehicle.
The TPMS module also communicates with the vehicle instrument cluster to provide the driver with appropriate warnings that show the importance of the condition detected and indicate the status/failure of TPMS components.
Tire Location
Because of the requirement for different pressure targets and thresholds for the front and rear tires, the TPMS module 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 module using an auto-location function. This function requires no manual intervention by the driver. The TPMS module 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 TPMS module 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 module 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 module can learn the new sensor identifications automatically. The learn function requires no manual intervention by the driver.
If a new sensor is fitted to the spare tire it must have its identification code programmed into the TPMS module using a Land Rover approved diagnostic system, or used on the vehicle as a 'running' wheel and the vehicle driven for 15 minutes at more than 12.5 mph (20 km/h).
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 fitted with a tire pressure sensor, the TPMS module can detect it, determine that it is the spare tire and monitor its pressure and issue warnings to the driver accordingly. If the TPMS module expects the spare tire to be fitted with a tire pressure sensor and it does not, the module will not show a fault to the driver, however a fault code will be stored in the TPMS module.
If the spare tire is being monitored and the driver replaces a flat 'running' tire with the spare tire, the module 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.
System Operation
Each time the vehicle is driven, the TPMS module 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 TPMS module via a LIN bus.
The system enters 'parking mode' after the vehicle speed has been less than 12.5 mph (20 km/h) for 12 minutes. In parking mode the tire pressure sensors transmit a coded signal to the module 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.
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 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 TPMS 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 12.5 mph (20 km/h), the initiators fire in turn for 6 seconds 433MHz systems or for 18 seconds on 315 MHz systems in the following order:
^ Front left
^ 6 second pause (for the TPMS module 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 module 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 module. The process is known as 'Auto Location' and takes 3 to 4 minutes on 433 MHz systems and 7 to 8 minutes on 315 MHz systems to complete. During this period the tire sensors transmit at regular intervals, once every 5 seconds on 433 MHz systems and once every 15 seconds on 315 MHz systems. 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.
RF Receiver
The RF receiver is mounted behind the overhead console and connects to the vehicle harness via a fly lead. A 3 way electrical connector faces the rear of the vehicle.
The RF receiver receives transmissions from each of the tire pressure sensors via an internal antenna. This information is then communicated to the TPMS module via a dedicated Local Interconnect Network (LIN) 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 TPMS module.
The TPMS module 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 TPMS module via a LIN bus. The module 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' information 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.
The RF transmission from the sensor contains a unique identification code in its transmission data, so that the TPMS module can identify the tire on the vehicle. If the sensor is replaced on a 'running' wheel, the new sensor identification will be learned 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 TPMS 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.
The replacement spare wheel may also be programmed to the vehicle 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.
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 messages from the TPMS module. The warning indicator is illuminated by the cluster software for 3 seconds when the ignition is switched to position II for a bulb check.
NOTE: If the vehicle is not fitted with the TPMS, the warning indicator will not illuminate at any time.
Controller Area Network (CAN)
The TPMS module sends and receives a number of digital messages via the medium speed 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.
Received Messages
The TPMS module receives the messages shown in the following table.
Transmitted Messages
The TPMS module transmits the messages shown in the following table.
Message
Diagnostics
The TPMS module has a diagnostic connection via the medium speed CAN to enable system status and faults to be retrieved using a Land Rover approved diagnostic system.
Additionally, an on-board diagnostic routine within the TPMS module constantly monitors the system and alerts the driver to system faults by illuminating the amber warning indicator, emitting a tone from the instrument cluster sounder 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 TPMS module 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 TPMS module. The module 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 TPMS module will transmit a message to display 'FL Tire Not Monitored' for example in the message center. The dealer should interrogate the TPMS module 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 TPMS module 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 module 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.
CONTROL DIAGRAM
NOTE: A = Hardwired; F = RF Transmission; N = Medium Speed CAN Bus; 0 = LIN bus; W = LF Transmission
