Tyre pressure measurement on a vehicle

A tyre pressure control arrangement for a vehicle having at least two tyres connected to an air supply. Each tyre is connected to an air supply via a respective supply line having a respective valve means (223) and the respective valve means is connected to a second valve means (222). The arrangement further comprises a pressures sensor (38) between the respective valve means (223) and the second valve means (222). The respective valve means (223) is closed while the supply line is connected to a reference pressure supply and the reference pressure in the supply line is monitored for a pre-determined period of time by a control system on the vehicle to detect whether there are an leaks in the arrangement.