Pokanoket

My altimeter continually shows either MINUS 200 feet or MINUS 400 feet. I have gone through, what I think, are the reset procedures but she always comes back to negative readings.

GX is 700 miles old...any suggestions or thoughts ??

Rx900

no fix, i think. mine does that sometimes but it goes back to the positive reading. it just does that, i guess. one day -200ft, then tomorow, 150ft.

SacKen

Mine too. After noticing that the elevation of my house (~200 ft) fluctuated a couple hundred feet each day, I decided to test it. On my way up to Lake Tahoe (elevation ~8000 ft at the peak) a couple months ago, I synchronized the trucks reading with the elevation signs on the side of the highway. After a couple thousand feet, it was noticably off again as I passed more elevation signs. On the way back home a few days later, it was way off at all the markings, just like before I calibrated it. The only difference should be the air pressure due to a different weather system in the area. Which has led me to believe that Lexus is simply using the barometric pressure to calculate altitude! If this is true, why they didn't just use GPS, I don't know. Or maybe they are using GPS but went cheap on us and are using a very inaccurate version.

Oh well... I haven't used it since then and have tagged it as another useless feature, along with the temp (which will hopefully get fixed at my 5k).

Rx900

i just ignore the altitude, but my temp gauge is ok. usually its only bout 3-5 degrees off.

tetra7

Most common altimeter are based upon barometric pressure (i.e. READ relative air pressure). To verify this, wait for a day when a front is rolling in. You will see the pressure gauge drop as the front rolls in...this is exactly what happens to both my heart rate monitor (which tells altimeter) and the GX. If you have doubts, bring up a a contour map (they are online - google for it) of your area and see how off it maybe. On average, I have found mine to be 80 to 85% accurate (minus any large weather disturbances).

Pokanoket

But Tetra7, let's review:

My altimeter still reads MINUS 200 feet and one minute later, will read MINUS 50 feet. She has never risen her head to sea level. South Louisiana is essentially sea level. As to air pressure, hmm, we would need a meteorologist answer this one because during the aforementioned one minute noted previously, no cold or warm front was encountered.

I hopefully will an explanation regarding this conundrum within the next week and will post the "Lexus response".

2004 Lexus GX 470
Blizzard Pearl on Ivory
Pimped with every available option except Lexux Link

Rx900

i would just ignore it if i were you, it'll just drive us all crazy! just put it on temperature mode to ignore it. besides, how many times would u use it anyway, even if you go to the mountains a lot, the altitude is on the side of the road!!!

tetra7

pokanoket

it does sound like your system maybe miscalibrated or malfunctioning. Is it possible you really are below sealevel that badly? Where I live, I am approx 600 ft above sealevel. Pull up a contour map and check to be certain.

SacKen

When the display is in altimeter mode, use the arrow buttons to adjust it up or down to recalibrate it to what it should be. If it was never done, then you have never been above sea level because it was probably last calibrated in Japan.

To test if the system is indeed using a pressure system, use tetra7's advise. Record the atmospheric pressure that the GX displays on one of the "modes", then set the altimeter to the correct value for your house. The next time you get in and the altimeter is off, record the new pressure and by how much the altitude is off. You should see a higher reading when the pressure drops and a lower reading when the pressure increases.

If it does work this way, simply calibrate it at a known location each day that you plan to use it.

bobgore

It's a barometric altimeter just like in airplanes. It will read a different altitude while it sits in your driveway as the atmospheric pressure changes. All you can do it set it to a known altitude and hope the pressure does not fluctuate too much. This isn't a problem while flying because including the barometric pressure reading is standard when making initial radio contact with local facilities.

looknow12

You have to calibrate it like any altimeter. Use the + and - buttons below the display,

bobgore

The owners' manual says the barometric pressure is taken inside the car. In that case the air pressure will fluctuate depending on the speed of the car, position of the windows and sunroof, air conditioning fan speed and settings, the number of words per minute your wife is using, whether you had Mexican food for lunch....

looknow12

The air pressure in the car will be near identical to the outside. The vehicle is not at all sealed. That's why a home barometer can work inside without external sensors.

bobgore

Not true. Bernouli's Principle. The faster air moves over an object, the lower the pressure...all things being equal. That's why cars have spoilers; to "spoil" the lift created by the pressure drop of the air passing over the top. However, in the case of a car, high pressure builds up at the bottom of the windshield. That's one of the reasons that the intake vents are there. When the air conditioner is on fresh, the pressure inside will be higher as opposed to when it is on recirculate. When you open a window inside pressure will fall. Now, I don't know if the effect is measurable with the Lexus barometer, but you might give it a try to open and close windows as you travel to see if it measures the fluctuation.

Since altitude measurement is inherent with GPS communication with three or more satellites, it is too bad Lexus doesn't take the information that the GPS is receiving and display it. That will give you altitude within feet regardless of the weather or any other factor.