Flat tire indicator on

You don't tell us what year your Tiguan is, so it's hard to be sure, but generally the tire pressure sensors that are mounted inside the tire itself have batteries that are only rated for about 5 years. If your car is older than that there's a good chance the battery has died, meaning you'll have to replace the sensor (batteries on those are not considered replaceable).

Of course, if one died, then there's a very good chance the other three won't be far behind, so if that's what happened, you had best replace all of them.