I found out my trye pressure monitoring system worked yesterday , just getting home from a trip into wales and the system said check tyre pressures , and the little orange wheel stayed lit, luckily I was only 2 miles from my local tyre place so I went in and there was a large screw that had gone between the tread blocks on the nearside rear wheel , pressure was down to 1-8 bar , cost me £15- 30 p for a repair job .Lot better than a new tyre