bileve

Our Japan assembled 2007 RX350 illuminated the tire pressure warning light on a photo shoot trip to Bristlecone Pine Scenic Area on Windy Ridge. It is located at 11,724 feet elevation above Alma, Colorado. The lamp stayed on until we returned to 8,000 feet. A bourdon tube hand gauge showed pressure of all four tires normal. Prior to trip tires had been set to factory recommended 30 psi and pressure warning system initialized per owners manual (page 306) at our 6,995 foot elevation residence in 68 degree garage. Ambient temperature during alert ranged from 34 to 43 degrees F. Load was driver, two passengers and light luggage.

Have I missed anything?

rxdriver

Temperature affects the pressure - as the temperature drops, the pressure drops. Living in the flat Midwest, I don't know if altitude is a factor or not.

Temperature usually drops the pressure by 1 psi for every 10 degrees colder.

If the RX350 sensors are like other Toyota/Lexus active sensors, they'll trip the light when one or more drops below 27 psi.

bileve

Measurements taken over the four years I owned 2002 RX300 show that setting tires to 30 psi at 6995 feet elevation residence resulted in reading of 27 psi next day in Plano, TX at 675 feet. I own two bourdon tube gauges of different manufacture and they agree. Consumer grade gauges are probably not compensated for altitude and temperature.

TripleDES

I know altitude affects pressure, but I'm not sure to what degree. The higher the altitude the thinner the air, thus reduced pressure. As an inverse expirement, fill your air to 30psi in >10k altitude and measure again when close to sea level. It would be interesting to see the results.

salimshah

Is it a Low pressure warning indicator or "out of safe range" warning system? [I don't have one but I would like to know]

Intutively, I think the pressure inside the tire to go up as you climb to a higher altitude (temp being the same). It would be awesome to know if gps (altitude compensation) is used

Salim

bileve

Tire gauge in this discussion is made in USA Meisner Accu-Gage part number 1025, 2 inch dial, 60 psi full scale. Google brought up these specifications that suggest the movement is alright under different ambient conditions:

All Accu-Gage® 1-1/2", 2" and 2-1/2" dial tire gauges are ANSI Commerical Grade B gauges, which is the best quality gauge typically used for tire pressure applications.
These tire gauges use a fully geared, solid brass precision movement with bronze bourdon tube. Unlike piston-plunger-type gauges, the bourdon tube movement is not affected by changes in temperature, humidity, altitude or air stream contaminants.
The mechanical accuracy rating is ± 2% from 25% to 75% of scale and ± 3% below 25% and above 75%.

A 15 psi tire gauge is accurate to ± 0.5 psi from 4 psi to 11 psi and is calibrated to ± 0.25 psi at 7.5 psi.
A 30 psi tire gauge is accurate to ± 0.6 psi from 8 psi to 22 psi and is calibrated to ± 0.5 psi at 15 psi.
A 60 psi tire gauge is accurate to +/- 1.2 psi from 15 to 45 psi and is calibrated to ± 1 psi at 30 psi.
A 100 psi tire gauge is accurate to ± 2 psi from 25 to 75 psi and is calibrated to ± 1.5 psi at 50 psi.
A 160 psi tire gauge is accurate to ± 3.2 psi from 40 - 120 and is calibrated to ± 2 psi at 80 psi.

The other gauge is a no-name made in Japan 60 psi 1 - 1/2 inch unit that gives same reading when alternated with Acu-Gage.

The within tire Lexus sensor is probably a piezo or other strain gauge device driving a radio transmitter.

I conclude the apparent pressure difference measured at altitude is related to absolute pressure being lower outside tire casing. The real issues are probably tire heating at speed, odd tire wear due change of tire shape and rolling resistance (or fuel economy). Radial tires probably hold their road contact shape better with changes in pressure. Dashboard displayed fuel consumption was better than 24 mpg and average speed 49 mph for this outing.

I'll try reducing tire pressure to 25 psi, resetting sensor then pumping them up to 30 psi again. Hope display doesn't trigger overpressure complaint.

salimshah

I am trying to learn how the tire pressure warning light in Lexus works. Is it low pressure warning only or out of range [both low and high]

After calibration ..
Does the tire pressure warning in Lexus light up when

a. Pressure is low
b. Pressure is high
c. Both of the above.

Salim

jim256

For the 2007, it directly measures pressure and triggers if it drops below some threshold. I'm not sure what happens if one or more is exceedingly high, nor do I know if the '07 has any reset capability.

Pre-2007, the system measures wheel rotation of each wheel and lights if one or more is rotating at a different rate than the standard (based on the reset), indicating the pressure and overall diameter is less. I have read, somewhere, that it triggers at a 7% difference in rotation speed. 'Can't verify that, however. I had this system on an '05 Highlander and it works, mine triggered at about 26 lbs when the rest were at 30. The RXh does not have either system, pre-2007.

bileve

Reduced four tires to 27 psi at room temperature. Initialized the tire pressure warning system. Pumped the tires back to recommended 30 psi and the warning lamp remains extinguished. That should give three more pounds of pressure margin for wide temperature and altitude swings perched here on the Rampart Range. Note that the spare is set to 40 psi. That tells me the system doesn't respond to over pressure.

Scott_lmtd

Just FYI, found a few things out after my 2 week old RX350 had the entire front end replaced due to kid running a light and hit me..... Just a bit of pity....

My 350 came from the factory with the tires at 44PSI, door states 30 PSI, Dealership (Stevinson for all of us in CO) said 34/35 PSI is correct. Also, check your spare, as bileve is indicating that will set off the system.

Yes I beleive you are correct bileve, no over-pressure indication, 44PSI, I was shocked, but good gas mileage. The factory setting I was told is 27 PSI to get an alarm, but you can reset/re-cal by using the switch under the drivers steering wheel.

bileve

Lexus of Colorado Springs delivered our RX350 in July with five tires set to 40 psi. Perhaps the factory hoped the tires wouldn't bleed too much air during ocean transport or time sitting on lot. The ride is harsh at that pressure and the recommended 30 pounds seems just on the cusp between comfort and feeling too much of the road.

DakotaRX

I haven't had any trouble with the tire pressure monitor but thought I would relay this. I towed a 3000 lb U-Haul trailer 1300 miles from ND to Tacoma, WA with the tire pressure set at 35 psi front and 36 psi back. I normally run it at 34 psi all around but with the extra weight of the trailer I went with 35/36. The only reason I put the back at 36 was the thought that the extra weight back there would make the tires squat a bit more and I know that the 2005 RX330 uses the "tire rotation" method of pressure monitor. Tire pressure was checked every morning at cold temp using a digital gage. As I said, had no problems with the pressure monitor. As for running your tires at 30 psi as listed on the door sticker that's up to you. Myself I have tried mine at 32 psi and 34 psi and have noticed no difference in ride. I leave it at 34 psi as I believe this does help the gas milage a bit due to less rolling resistance when set higher. I'm sure setting it at 40 psi would be even better for milage but as noted the ride is going to suffer.

2005 RX330 Thundercloud, Gray/Black Interior with Black Birdseye Maple, NAV, ML, HID with AFS, Rain sensing wipers, Towing Package with OEM Hitch, 18" Thundercloud rims with MXV4's.
1998 GS300 (Previous and 1st Lexus)