ive had my 2003 x350 3litre petrol for six weeks and after the 270 mile journey home i discovered the o/s front tyre only had 18 punds pressure in it,should be 32, no warning light or message came on in the car, the car is on 20 inch wheels, ive since learned that the tyre loses 6 pound of pressure evey 7 days so i took it to quick fit who said if they put a standard valve in it then i would get a dash light or warning but from what i can gather the warning comes on when 25 percent of pressure is lost, being that i drove it for long enough with only 18 in it with no warning does this mean this sensor is broken or can i safely put a normal valve in it?
i would appreciate any advice