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False warning lights

I have a 2004 Lexus LS430, and I frequently get a dashboard warning that I have “low tire pressure”, but when I check the tires, they are all OK. There is a reset button deep under the dash that is difficult to reach. I would appreciate hearing from anyone who might know what is causing this, and if there is an easy fix. Thank you.

If your tire pressures are all good then I would suspect one of your TPMS sensors is the culprit.

Those things are located inside the tires, being basically built into the stems. They go bad from time to time.
I understand that, when they need replacing, that some cars need that done by the dealer. There’s some sort of ‘learn’ procedure that has to be followed to get the new one to be part of the system.
That may not be the case with Lexus but worth finding out.

Check the pressure in the spare tire.

+1 to casper’s suggestion.
All too often, people do not bother to check the pressure in their spare tire, and IF your spare contains a TPMS sensor (some do, some don’t), low pressure in the spare could be to blame.

If the spare’s pressure is not the problem, then it would appear that one or more of the TPMS sensors in your road tires has a battery that is going bad. After at least 8 years of service, that would certainly be possible.

As these “Mommy” cars age, they can become a real pain in the butt as the various sensors and the warning messages they generate become difficult and expensive to deal with…The third owners of these 8-15 year old cars just want basic transportation and are not interested in a rolling toy-box…

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I agree with casper and VDC.

I didn’t think of that. Great tip of checking the spare.

The Low Tire Pressure light on my wife’s 06 Sienna uses the ABS system, not tire sensors. A tire with low pressure will rotate a a different rate than the other tires thus triggering the trigger light. The TPMS has to be reset when the tires are rotated or replaced. The procedure is in your Owner’s manual. The manual will also explain which type of TPMS is in the Lexus.

I suggest verifying the 4 tires are at the correct pressure and then resetting the TPMS following the procedure in the manual.

Ed B.

Thanks for all the comments. After you told me about the spare tire, I checked it and found it had only 20psi. I inflated it and hope that solves the problem. Thanks again all.

The spare tire is not monitored on this car. Follow the advise edb1961 gave and use the reset proceedure in the owners manual.

There are no tire pressure sensors on the LS430, the system monitors tire circumference to detect a low tire. When one or more tires are replaced the circumference must be relearned using the reset proceedure.

  • nevada_545

tpms works by checking and referencing the rotation of the tires. With lower pressure the circumference ergo the rotation speed changes and that what the sensor picks up.

A decent tire shop can also work fine with TMPS replacement if needed. There is nothing mysterious about the system. It is too bad one generic light shows up in many vehicles where mine actually shows the tire pressure of each tire and offending culprit. Maybe a tire shop can read the “low” tire and find the failing sensor. Not a big deal.

One comment was made that this particular car doesn’t have those sensors but now I’m curious:

Can tire shops indeed read the tire pressure directly off the sensor? Some sort of ‘wand’ reader you wave over the tire, if you will?

This tool can read tire pressure/tempuratue and registration code from a tire pressure sensor.

tpms s can’t tell exect pressure they can tell when the pressure drops below a preset amount

I have a 2008 Lexus RX 350. I’ve had several of the TPMS sensors replaced but a few days after I get it home the light always seems to come back on. The tires are properly inflated. The mechanic says that the other sensor batteries are fine and that the control unit is losing contact with the sensors. He did not say, but he implied that fixing it permanently may require replacing the control unit. (I assume he means the computer module)

Is this possible - or has he perhaps just missed a bad battery when he scanned it? What sort of wireless connection do these sensors use? Bluetooth of some kind?