Hummer H1 Central tire inflation System (CTIS) explained.
The unique CTIS feature on the Hummer H1 allows you to inflate and deflate
the tires on your Hummer while you are driving. Changing the tire
inflation of your Hummer to accommodate different terrain greatly
increases its mobility and comfort both off-road and on.
With the flip of a dash mounted switch, air is pumped to the front tires, the rear tires, or all four tires at once. Pressure is monitored by a dash mounted pressure gauge.