Not new to the XTerra, I've had 2000, now a 2005. Love both. On the 2005, there are tire pressure sensors that, when the pressure goes below 35psi, usually on every cold morning for obvious reasons, the light comes on. I've upped the pressure to 38psi to remedy this and works. Now, the light has come on and stays on. once in a great while it goes out, only to come back on again. I've checked the pressure in all 5 tires, even though the spare does not have a sensor, but the light stays on. Could this be a bad sensor, or worse, in the receiver of the vehicle. I know most of the avid off-roaders take them out so they don't have to listen to the screaming alarm when they air down, I didn't do that. Any thoughts on this?

Try filling them with Nitrogen and see what happens.