[Randall Raines]

It's the switch for resetting the Run-flat indicator light as indicated by "mini_mart" here's how to reset / use the button , from a previous thread.

Quote: Originally Posted by Randall Raines (original)

Run-flat Indicator light / Tyre Pressure warning light.

Initialising the system, after changing a wheel, tyre, or just doing the pressures (make sure all the tyre pressures are correct), even if the light isn't already on .

Just before you're about to go for a drive, start the car up (don't drive off), press the button (keeping it pressed until the run-flat warning light comes on, then release it) under the hand brake that looks like a cross section of a tyre with a ! in it eg.

( ! )

If your light is already on it should go of and come back on again (if not already on it should come on), set of on your journey (drive), a few yards down the road it should go off (Reset) .