The VSA modulator-control unit detects a state that the pressure of one tyre is relatively lower than pressure of the other three tyres. Deflation detection is performed by monitoring the rotation speed of four wheels.

When the system detects the deflation of a tyre (from 10 % to 30 % deflation from recommended pressure), the low tyre pressure indicator is turned on to inform the driver that a tyre is deflated.

Deflation of two tyres on diagonal position or three tyres are also detectable.

To detect tyre deflation with desired accuracy, it is necessary to learn the difference of rolling of the four tyres at recommended pressure (learning is started by initialization).