jimmer!

last week I was stopped at a light and for 3 seconds or so experienced a low ratcheting sound/vibration,
felt in the brake pedal. as it happened, it was surprising, but then went away.

related or not, soon after, my tire sensor dashboard light came on.

I didn't freak and checked the tire pressure at home.
all four were fine.

a day or 2 later, dropped by my tire shop to get it reset.
the guys were playing around the idea that the sensor battery (batteries) went out,
figuring that a reset wouldn't good any good. new sensors were needed.

knowing from this forum that a new sensor software programming was proprietary to lexus/toyota,
I dropped by my dealership and had them professionally checked.
all sensor and their batteries are 100%. surprising, my 430 is 6.5 years old. the batteries are said to go out after 5 or so years.
OK, they reset the dashboard light and I was on my way (after a $47 ouch.)
as I motored home, the light came on again.
at home, I checked the tire pressures, the passenger front was about 4 lbs. high, I adjusted it and started her up.
light is still on.
does this sound familiar to anyone?
any experience with a 'ghost' tire sensor indication or whatever?
thanks.

IStoSC

Hmmm...I have not had this exact experience with this but I did have a a few dead batteries in the past year and these sensors are VERY sensitive. Last week I had one that was a constant light and it was my driver front side tire which was slightly below 30psi. I refilled all to 33psi and the light went away. If you've got really low pressure or if there is an emergency the light will blink and you'll hear a beep...

Anyway, because you did go to the Lex dealership and dropped $47 bones on them basically not helping you I would bring the car back for another diagnostic on them and ask them to help you figure it out.

TooCoolSC

I've had the TPMS light come on twice, and on both occasions, it was the sensor battery. And like everyone says, they were literally within a couple of weeks of each other. When one goes, they all go in a short time. It's uncanny. When the second one went out, I had the three older ones replaced all at the same time. I thought it might be a little cheaper that way. Thought my service guy might feel sorry for me and give me a package deal. It pays to try to develop a relationship with them because they can write it up however they want....within reason.

Your situation is a confusing one, though, because you did what you were supposed to do and they told you all was well with the sensors. Just out of curiosity, did you get it checked at a Lexus or Toyota dealer? 9 times out of 10, it's going to be the battery, especially when (as you said) the car is at the age where the sensors typically go out. Did they think the sound/vibration you heard was relevant, or did they disregard it? If not the sensors, could the TPM system itself be at fault?

Habious

They can check the sensors to see if they're transmitting their signal...but they can't "check the batteries" in them as far as I know. The batteries are sealed inside the sensors (there's a pic of them floating around the forums somewhere).

And yes, your problem sounds exactly like the problem I had when my sensors started to go.

The sensors use a 3 volt Lithium cell...like a quarter-sized watch battery. Lithium cells are designed to give a constant voltage until they "just die"...which is why, when your watch battery dies, it usually "just dies" one day. The watch doesn't run slower and slower until it craps out. It's working one day, and dead the next morning.

Sometimes they'll fluctuate a little between the "working fine" and "dead" a few times before dying completely.

Give it a couple of days, the light on the dash will come on...and stay on. Then you can go back to the dealer and they can figure out which one is dead.

Then the option becomes "replace one" or "replace all".

If you've got the means, I highly recommend you just have them all replaced and get it over with. It's a PITA to replace each one as they fail.

jimmer!

hmm.
it's was a toyota dealer, that's my only option round here.
I was shown a printout of each sensor.
each was working, up to spec.
and the battery for each had a very good charge.
interestingly, I didn't mention the ratcheting sound to them, so you could have something there,
that the unit is on the fritz, but I'd think their diagnostics would have discovered that.
I'll report back when I look into it more or get back to the dealer.
if all else fails, I may need to go into phoenix (down the mountain) and have it tended to there,
but I'd have to wait for it.

thanks all for the advice.

here's a final thought:
the 430 tire psi is 33.
due to our elevation (56-5300 ft), the dealer and tire shop go to 35 psi,
compensating for the lack of air pressure.
I wonder if that's throwing the sensor off?

Bon

I'm going to go out on a limb and guess that the clicking sound you heard and felt was your brakes ABS pump cycling on. This is not necessarily a problem as the pump from time-to-time has to pump up its reservoir so it can modulate your brakes for you when call upon. That said, there isn't any relationship between your TPMS issues and the ABS pump.

Secondly, I don't get what you say about the relationship between your altitude and tire pressures. A tire air gauge reads "gauge" pressure not "absolute" pressure. This means that the tire gauge reading is correct for all altitudes and you should be consistent with the air pressure that you want in your tire. Again, that said, if you drive to a lower altitude your tire pressure will now be at a lower "gauge" pressure than when you filled them at altitude. The opposite occurs when you fill your tires at lower altitudes. Tires pressure will be higher when you drive to a higher altitude. This works because your tire has a specific amount of trapped air molecules inside. When the amount of air molecules outside of the tire increase/decrease due to altitude (or temperature) then the "gauge" air pressure in your tire will seemingly lower/raise accordingly. Confused yet? I'll shut up soon. I think your dealers & tire shops are concerned that you'll drive to a lower altitude and this will leave you with under-inflated tires so they slightly over-inflate them to avoid that situation. Done.

I chucked my TPMS a long time ago along with my run-flats so, I'm sorry, I can't help otherwise. Good luck!

Harold57

The TPS trip at a low pressure (I don't know what level that is but mine is well below 30psi). Pressures that are too high do not affect them, unless the design has changed, which is not likely.

I agree with Bon on the clicking noise likely being the ABS.

antigeek

It's been several years since I've read about the TPMS on CL, but I believe each sensor "sets" to the highest pressure it encounters. If it drops down x PSI, the light comes on.

I think the commenters are correct that the batteries are going, but I'd suggest the following first:
- add the pressure back to the tire you adjusted, and see if the light goes out
- if it does, adjust the tires to the pressure you want, then take the car back to the dealership and have them reset the sensors (there's some magnetic wand they use)

You may be able to get some more time from the current batteries if this is the case.
I don't remember if I replaced the batteries with a tire change, but it has been 8.5 years.

jimmer!

thanks for the speculation on the ratcheting sound.
APS pump makes sense.

as for the tire psi adjustment for my altitude, it's a head scratcher,
but they all do it here, so I don't know anything anymore.
the sensors do come in handy when working. a year ago, a small nail was detected
that normally would have gone unnoticed until too late.

and yes, bon, you've hurt my brain (it's too early).
I'll go back to them and see what they can figure out.
I'll let you know.
thanks.

jimmer!

well, I went to a phoenix lexus dealer and they found that
the passenger front sensor was bad. I had it replaced and
all is well. no more tire sensor light.
after calling the toyota dealer to inform them that they
were wrong about all four sensors being OK, I was told
that sometimes toyota diagnostics don't work on lexus'.
gee thanks. now I'm a bit wiser, but still out the $47 they
charged me.
thanks for your comments.

TooCoolSC

Glad it turned out to be something simple. Don't be surprised if another one goes out fairly soon. That's what happened to me. It was literally within a couple of weeks, I think.

If another one goes out soon, ask them if they would cut you some kind of package deal to replace the other 3. That's what I did and I think I probably saved a few bucks. It's not much, but it never hurts to ask to ensure the best deal possible. Then again, unhooking the whole system is the cheapest way to go.....and it's free. I didn't want to do that, though.

As (bad) luck would have it, I wound up trading the car in only a few months after having all the sensors replaced.

jimmer!

yeh, that occurred to me as I was driving back, up the mountain.
thanks for the advise, I may give 'em a call and see what they
think about the other sensors (longevity and package replacement
option).
all in all, it is nice to get this problem figured out and my trust-account
with the local toyota dealership in place.