Tire Monitoring System: Description and Operation
Tire Pressure Monitoring
Visual Identification
Wheels fitted with the tire low pressure sensor can be visually identified by the external metal lock nut and valve (1). All Jaguar non-tire pressure monitoring system wheels have a rubber valve fitted (2).
The tire pressure monitoring system monitors pressure in each tire including the full size spare tire (temporary-use spare wheels are not fitted with tire low pressure sensors and are consequently not monitored).
Tire Pressure Monitoring System - Component Location
Item Description
1 Tire pressure monitoring system antenna
2 Tire low pressure sensor
3 Instrument cluster
4 External antenna
5 Tire pressure monitoring system module
The purpose of the tire pressure monitoring system 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 specific markets.
The tire pressure monitoring system measures the pressure in each of the tires on the vehicle and issues warnings to the driver if any of the pressures deviate from a defined tolerance, which is dependant on the vehicle market and the size and type of tire fitted.
Note: During a blow out a very rapid reduction in tire 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 tire pressure monitoring system is to assist the driver in keeping the tires at the correct pressure, which may to reduce the likelihood of a tire blow out occurring.
Tire Pressure Monitoring System Module
The tire pressure monitoring system module is located with the parking aid module in the luggage compartment of the vehicle.
The tire pressure monitoring system module's main function is to detect the following:
- the tire pressure is below the recommended low tolerance value - under inflated tire
- the position of the tire on the vehicle.
The tire pressure monitoring system module communicates with the vehicle instrument cluster to provide the driver with appropriate warnings and also indicates the status/failure of tire pressure monitoring system components.
Tire Location
Because of the requirement for different pressure targets and thresholds for the front and rear tires, the tire pressure monitoring system module can identify the position 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 tire pressure monitoring system 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 pressure monitoring system module can automatically detect, under normal 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.
Spare Tire Identification
Depending on the vehicle specification, the spare tire may or may not be fitted with a tire pressure sensor. Temporary-use spare wheels are not fitted with sensors and are consequently not monitored.
If the spare tire is fitted with a tire pressure sensor, the tire pressure monitoring system module can detect it, determine that it is the spare tire and monitor its pressure and issue warnings to the driver accordingly. If the tire pressure monitoring system module does not detect a spare tire pressure sensor, the tire pressure monitoring system module will not show a fault to the driver, however a fault code will be stored in the tire pressure monitoring system module.
If the spare tire is being monitored and the driver replaces a flat road tire with the spare tire, the tire pressure monitoring system 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. Warnings will only be displayed for 20 seconds after the ignition is switched on.
Tire Low Pressure Sensor
The tire pressure monitoring system uses 'active' tire low 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. The tire low pressure sensors transmit their Radio Frequency (RF) signals at either 315 MHz or 433 MHz dependent on market requirements.
The tire low pressure sensor periodically measure the pressure and temperature of the air inside the tire. Pressure and temperature measurements are transmitted periodically to the external RF antenna on the vehicle.
The tire low pressure sensors are self-contained units which have no electrical connections into or out of the tire low pressure sensor.
The care points detailed in 'Tire Changing' must be followed to avoid damage to the tire low pressure sensor. If the tire low pressure sensor is removed, the nut, valve core, cap, seal and washer must also be replaced and the tire low pressure sensor tightened to the correct torque value. It is also recommended that the nut, valve core, cap, seal and washer are replaced at every tire change.
The RF transmission from the tire low pressure sensor contains a unique identification code in its transmission data, so that the tire pressure monitoring system module can identify the tire on the vehicle. If the tire low pressure sensor is replaced on a road wheel, the new sensor identification will be learned when the vehicle is first driven at a speed of more than 20 km/h (12.5 miles/h) for 15 minutes. If a new tire low pressure sensor is fitted to the spare wheel, the identification for that tire low pressure sensor must be programmed into the tire pressure monitoring system module using a Jaguar approved diagnostic tool 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 tire low pressure sensor.
In order to conserve battery power, the tire pressure monitoring system 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 approximately 20 kph (12.5 mile/h).
Antenna
The antennas are located near the front of the front wheel arches, and the rear of the rear wheel arches. The tire pressure monitoring system has four antennas. Each antenna has a connector which connects with the body wiring harness.
The antenna is a passive, Low Frequency (LF) transmitter. Each antenna is controlled by the tire pressure monitoring system module and provides an auto-location feature to identify tire positions on the vehicle.
The tire pressure monitoring system module energizes each antenna in turn using LF drivers. The corresponding tire low pressure sensor detects the resulting LF transmission and modifies the mode status within the RF transmission. This data is received by the tire pressure monitoring system module through the external RF antenna. The tire pressure monitoring system module can then determine which sensor is transmitting and its location on the vehicle.
External Antenna
The tire pressure monitoring system external antenna is located at the rear of the vehicle and is mounted between the spare wheel well and rear subframe.
The unit receives tire pressure, temperature and acceleration readings from each tire and interfaces with the tire pressure monitoring system module. The tire pressure monitoring system module then transmits the appropriate messages to the instrument cluster.
The unit also receives further information from each tire pressure sensor concerning wheel identification, mode status and the condition of the tire pressure sensor battery.
Instrument Cluster Indications
Item Description
1 Low tire pressure warning indicator
2 Secondary amber warning indicator
3 Message center
Warnings are displayed by the low tire pressure warning indicator, the secondary amber warning indicator and a text message displayed in the message center.
The warning indicators are driven by controller area network (CAN) messages from the tire pressure monitoring system module. The warning indicators are illuminated by the instrument cluster software for three seconds when the ignition is switched to position II for a bulb check.
Note: If the vehicle is not fitted with the tire pressure monitoring system, the warning indicators will not illuminate at any time.
System Operation
The tire low pressure sensor transmits by RF (315 MHz or 433 MHz depending on market) signal. These signals contains data which corresponds to tire low pressure sensor identification, tire pressure, tire temperature, acceleration and tire low pressure sensor mode.
Each time the vehicle is driven, the tire pressure monitoring system module activates each LF antenna in turn. The corresponding tire low pressure sensor detects the LF signal and responds by modifying the mode status within the RF transmission.
The system enters 'parking mode' after the vehicle speed has been less than 20 km/h (12.5 miles/h) for 12 minutes. In parking mode the tire low pressure sensors transmit a coded signal to the tire pressure monitoring system module once every 13 hours. If the tire pressure decreases by more than 0.06 bar (1 lbf/in2) the tire low pressure sensor will transmit more often as pressure is 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 0.06 bar (1 lbf/in2) the tire low pressure sensor will transmit more often as pressure is lost.
As each wheel responds to the LF signal from the tire pressure monitoring system 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 20 km/h (12.5 miles/h), the antennas fire in turn for 6 seconds on all except North American specification vehicles or for 18 seconds on North American specification only vehicles in the following order:
- Front left
- Six second pause (for the tire pressure monitoring system module to detect a response from the tire low pressure sensor)
- Front right
- Six second pause
- Rear right
- Six second pause
- Rear left
- Six second pause
Each tire low pressure sensor responds in turn so the tire pressure monitoring system module can establish the tire low pressure sensor positions at the start of the drive cycle. This process is repeated up to three times but less if the tire low pressure sensor positions are already known in the tire pressure monitoring system module. This process is known as 'Auto Location' and takes three to four minutes on all except North American specification vehicles and seven to eight minutes on North American specification vehicles to complete. During this period the tire low pressure sensors transmit at regular intervals, once every 5 seconds on all except North American specification vehicles and once every 15 seconds on North American specification vehicles. For the remainder of the drive cycle the tire low pressure sensors transmit once every 60 seconds or if a change in tire pressure is sensed until the vehicle stops and the tire pressure monitoring system returns to parking mode.
Once the wheel position is established, the antennas stop firing and do not fire again until the vehicle has been parked for more than 15 minutes. The signal transmissions from each tire low pressure sensor continue at one minute intervals whilst the vehicle is being driven. This transmission is to monitor the tire pressure. The warning occurs at 25% deflation and comprises of message center amber secondary warning light, the low tire pressure warning indicator and an appropriate message displayed in the instrument cluster message center. The message center will also display additional information about the position of the affected wheel(s).