Description & Operation (page 5 of 13)

 
Tire Location  
 
Because of the requirement for different pressure targets and thresholds for the front and rear tires, the TPMS 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 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 TPMS module can automatically detect, under all operating conditions, the following:  
 

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one or more tire pressure sensors have been replaced  

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one or more tire pressure sensor identifications are missing  

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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  

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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 vehicle are changed, the module 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.  
 
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.  
 

System Operation  

Each time the vehicle is driven, the TPMS module commands each initiator to transmit a LF (125 KHz) signal to each 
pressure sensor in turn. This is received by the tire pressure sensor which passes its identification code and tire 
information to the TPMS module log. The senosr then transmits an RF (315 or 433 MHz depending on market) signal to 
the module. This signal contains coded data which corresponds to sensor identification, tire pressure, tire temperature 
and acceleration data.  
 
The system enters 'parking mode' after the vehicle speed has been less than 12.5 mph (20km/h) for 12 minutes. In 
parking mode the tire pressure sensors transmit 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 132 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 on all except NAS vehicles or for 18 seconds on NAS only vehicles in the 
following order:  
 

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Front left  

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6 second pause (for the TPMS module to detect a response from the tire pressure sensor)  

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Front right  

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6 second pause  

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Rear right  

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6 second pause  

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Rear left  

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6 second pause.