I know that this has been covered ad nauseum in other posts, but I thought I'd share some new information with everyone.

It has been established that the tire pressure warning light will illuminate because the tires are either a.) grossly under inflated or b.) one (or more) of the tires is significantly less inflated than the rest. By 'significantly less', several people have hypothesized that it would require a difference in pressure of at least 5+ psi. Apparently, this is not the case.

While recently ripping some SWEET donuts in the local ski area parking lot, I had the tire pressure light illuminate. Because I was throwing up tons of gravel in the process (did I mention how SWEET the donuts were??), I figured, "Great, a rock flew up and somehow damaged the sensor. There's no way I could have lost a ton of air doing that."

Upon returning home a couple days later (with the warning light still illuminated), I checked the tires with a digital gauge, and it would seem to backup my theory - 3 of the tires were at 35 PSI, but the drivers' side front tire was 32.5 PSI. A 2.5 PSI difference hardly seemed like enough to trigger the warning light. I topped off the slightly low tire anyway and planned to call the dealership about getting the light checked out.

Lo and behold, after squirting in the 2.5 PSI and driving for a mile or two, the light turned off!

Moral of the story: Apparently, that tire pressure warning system is REALLY sensative. Even a 2.5 PSI difference can trigger it!

FYI,

John P.

Side note: not sure how the hell I lost any pressure at all whipping donuts. I guess they were even sweeter than I thought! :-)

I drove up to 10,000ft'ish. The warning light came on.

Once I got back down to about 3,000ft on the way home, the warning light went out.

Seems these things are also sensative to the Altitude. Or my tires change PSI depending on the Altitude I'm at.

That's what caused it.

I have had tires as much as 3-5psi off and the light hadn't come on. So maybe some systems are more sesitive than others.

Your tire pressure should increase as you gain altitude. I've been to 10,000ft+ several times and have not had the light illuminate.

This is incorrect. While wheeling at higher elevations you have to constantly (if wheeling in snow) get out and let even more out. Consequently, on the way down you need to stop at a half way point and air up to prevent blowing a bead.

I have had my light on for more than 70% of owning the X (2 years in Feb) - I don't get it... I just ignore it now.

Hey as long as we're talking about strange issues with the tire pressure monitoring system (TPMS), here's one I haven't seen discussed yet. About a month ago I was driving through Big Pine CA. about 3 hours from my home and the TPMS light came on for about a minute and then went off. I stopped and checked and the pressures were fine. Two weeks later it happened again in the same area so I just ignored it. It occurs to me now that the TPMS system operates with a radio frequency and that the Caltech Radio Observatory http://www.ovro.caltech.edu/ is just outside of town there. Do you think a 140 foot diameter satellite dish that can talk to deep space has enough power to upset my TPMS?

The system is sensitive.

The same thing happens on my '04 350Z. The TPMS light comes on if the TPMS thinks the pressure drops below 30psi. 30psi in TPMS land is 34lbs in reality. I keep 36psi in the Z tires.

Haven't figured it out yet on my '06 OR, though, as I just bought it 2 months ago and the light came on for the first time yesterday.

Maybe it's just been a really long day, and I'm not computing this right in my head, but aren't you both saying the same thing? Tire pressure increases with elevation, which means it decreases when you loose elevation, hence having to air up half way down because of the decrease in pressure..

Or did you mean the pressure in your tires increase as you go lower in elevation? Because if so, thats incorrect. But I don't think you meant that.