Need help..everytime I start my Volkswagen Touareg the check tire pressure light comes on and stays on..what is the problem?

There are numerous tech bulletins on this. You need to see your VW dealer and it should be taken care of by them. Make sure you physically check your tire pressures to make sure that the system is at fault and that you don't really have a tire that is low.

If you have had your tyres replaced it is likely the tpv tyre pressure valve was removed and now the actual pressure cannot be sent as the valve is a normal one. Just had the same problem, also saying spare wheel tyre pressure low- normal valves were used when the idiots replaced my tyres!