The Nissan Pathfinder, like many other models of car, comes with an automatic tire pressure sensor. This sensor, which received input from all four of your tires, won't do anything until the pressure drops below the necessary level. When that happens a light on your dashboard will tell you that your pressure is low. The process for fixing your tires, and thus turning off that light, is a fairly simple one to complete.
Remove the caps on your tires and check the tire pressure. Make sure that the tires are "cold," which means they haven't been driven in several hours so there's no heat from friction. Heat increases the pressure and can give you an incorrect reading on your gauge.
Check the tire pressure that your gauge reads against the pressure listed on the tire. For instance, if your gauge reads that the tire pressure is 32 psi, but the tire is supposed to be inflated at 35 psi, then you need to inflate the tire. Once the tires are all brought up to their proper pressure the problem should be taken care of.
Turn on the vehicle after the tires have all been filled to their proper levels. The tire pressure light should turn off, but if it's still on then drive a short distance to see if it turns off. If it does not then re-check your tire pressure with a different gauge to make sure the reading is the same. If it is then the sensors might be damaged, in which case you should check your warranty and consult with a professional mechanic.
