Tpms system operation (Freelander 2)

Every time the vehicle is driven, the TPMS software activates each actuator to transmit a low frequency 125 kHz signal to each tire pressure sensor. The low frequency signal is received by the tire pressure sensor. In response, the sensor transmits a high frequency signal of 315 or 433 MHz (depending on the market) to the high frequency receiver. The signal contains coded information containing the sensor identification, air pressure, air temperature and acceleration. This signal is then transmitted to the CJB via the ISO 9141 K bus.

If the vehicle has been stationary for more than 15 minutes and then moves at a speed greater than 20 km/h, each actuator in turn transmits a low-frequency signal for 18 seconds in the following order:

• Front left
• Front right
• Rear right
• Rear left

Each tire pressure sensor responds in turn so that the TPMS software can determine the location of the sensors at the beginning of the driving cycle. This procedure is repeated up to three times, or less if the sensor locations are already known. This procedure is called "automatic location" and takes 2 to 4 minutes.

During this time, the pressure sensors transmit a signal at regular intervals of 5 seconds (15 seconds on vehicles for the North American market). Thereafter, during the driving cycle, the pressure sensors transmit a signal every 60 seconds, or more frequently if a change in tire pressure is detected, until the vehicle is stopped and the TPMS returns to Park mode.

Once the wheel position is set, the actuators stop emitting a low frequency signal until the vehicle comes to a stop and the parking time exceeds 15 minutes.



A warning will appear on the instrument cluster message center display if the tire pressure drops to 25% of the nominal pressure. The displayed message will also include information about the position(s) of the faulty wheel(s).

If the vehicle speed is below 20 km/h (12 mph) for 15 minutes, the TPMS system switches to Parking Mode. In Parking Mode, the tire pressure sensors transmit a coded high-frequency signal once every 13 hours. If the pressure drops by more than 0.6 bar (1 psi), the sensor sends a signal more frequently.

(The article is based on information from the website: «www.LRman.ru»)

The spare tire pressure sensor also transmits a signal every 13 hours, similar to the sensors for the working wheels in Park mode. If the pressure drops by more than 0.6 bar (1 psi), the sensor sends a signal more frequently.

Activators

There are 4 activators installed on the car. The front activators are located near the front of the front wheel arches, behind the mudguards. The rear activators are located at the rear of the rear wheel arches, behind the mudguards. Each activator has a connector connected to the body wiring harness.

The activator is a passive low-frequency transmitter. Activators transmit their signals to the tire pressure sensors, prompting them to change the mode status.

TPMS excites each actuator in turn using low-frequency pulses. The corresponding tire pressure sensor detects the low-frequency signal and changes the mode status in high-frequency transmission based on this signal.