What's the deal with this stupid low tire pressure warning light on my dash?

First, how does it sense the tire pressure?
Two, why is it not going off even when the tire pressure is at the recommended oem pressure? I've even gone 5-10 lbs higher than oem recommends and still it won't turn off.

i will refer you to the free factory service manual from this site again:

http://www.nicoclub.com/FSM/Quest/2004_Quest/wt.pdf

start at page WT-7

is it showing the pressures on your display as stated on WT-9?

check the spare? i dunno if it also has a sensor in the valve stem, like the other tires...

also another member did a general FAQ for TPMS:

faq-tire-pressure-monitoring-system-tpms-t330539.html

try that before going to a stealership to get an inoperative sensor replaced

sucks that the little battery in each of those sensors can not be changed out; you'll need to spend $$$ for a whole unit