reset the tire pressure monitoring system, to do so, you need to get your key fob, and put your ignition key in the ignition, turn it to the accesories position, and simultaneously press the lock and unlock buttons on the key fob. hold them until the truck honks the horn.
then take something to let out air in the tires, you need to start with the left front then go to the right front, then the right rear, then the left rear.
start at the left front, drop the pressure in the tire until the horn beeps, -usually takes 8 seconds or so. then repeat on the other tires in the order i told you above.
or you can get the J tool for the TPM's and use that.
anyways, after you finish with the final tire, the horn will honk again, then you know your done. usually honks 2 times.
and then you can turn the key off, and set your tire pressures.