miket000

You likely have a bad tpms sensor. The second time they read each tpms sensor they likely did the tires in a different order. I'd let a few psi out of one tire at a time. Watch the dash to figure out which is the faulty one.

Or maybe...
It is possible they didn't program the codes correctly.
When I watched discount tire record and enter my tpms codes their computer had a specific sequence to follow.

It was similar to watching my wife go grocery shopping. Not much rhyme or reason to it, but it worked. The sequence went something like this. He inputted each tire into his computer. Then he plugged into the obd port. Next he continued to retrace his previous grocery path around the car reading each tire again. Lastly he plugged back into the obd for a final "save".

rnlex07

Thank you so much miket000 for the quick response!. Your response in regard to the position of the "0" in the 1st and 2nd try makes sense. I was able to confirm the TPMS in question by inflating each tire to 40 and watch the PSI dash numbers go up after I'm done with each tire. It is the Rear left tire (sitting in the driver's seat). I will e-mail the tire shop and will provide update with the results.

Thank you again very much!

DrQuality

For the 2007 Lexus LS460, I have just confirmed that the TPMS 'telltale' low pressure warning & yellow warning lights have a built-in 'floor' so as to trigger at no lower than 26-27psi.

I did the TPMS tire pressure warning initializing/benchmarking/resetting process … as described in the 2007 Lexus LS460 Owner's Manual (page 513) … when all five tires were all sensing at 30psi on the TFT Multi-Information Display. The telltales are supposed to be set to 25% less than the benchmark (an undocumented parameter, but general conventional wisdom within these boards). That implies, that, were there no telltale floor, the telltales would have been set to trigger at about 22.5psi.

Nevertheless, the telltales triggered at 26-27psi. (I attribute that variance to the undocumented method of 'rounding/truncating' being used to display integer psi values.) That trigger floor works out, btw, to be almost exactly 20% less than the generally recommended pressure of 33psi.

From all that, I am going to surmise the (undocumented) 'rule' is that the telltales are set to trigger at 20% of the initialized/benchmarked/reset pressure, with the minimum allowable initialized/benchmarked/reset pressure being 33psi.

That there is a telltale 'floor' is actually subtly implied in the 2007 Lexus LS460 Owner's Manual (page 513) when it states that "the tire pressure warning system must be initialized(/benchmarked/reset) … when driving with the tires inflated to a higher than standard tire pressure."

Further that implies the advisement in the 2007 Lexus LS460 Owner's Manual (page 598) that "when the battery is removed or discharged, the tire pressure warning system must be initialized(/benchmarked/reset)" is almost certainly moot … if your tires are sensing at 33psi or less.

Summarized another way, it appears the TPMS initializing/benchmarking/resetting pressure process is really only intended for use when the driver is, for whatever reason, running tires at a pressure above the generally recommended pressure of 33psi … and the driver wants to ensure that the telltales trigger at higher values accordingly.

As an aside, I saw a number of discussions on these boards regarding pricing & sourcing of replacement sensors. What I discovered currently (mid-2021) regarding that is that (1) a Denso 5500103 sensor can be sourced from Amazon [ https://amzn.to/3AUxtBH ] or RockAuto [ https://bit.ly/3y37Kp4 ] or DensoProducts [ https://bit.ly/3B1MxxL ] for about $30, (2) that eBay has a number of vendors selling a set of four no-name-brand sensors to replace Toyota 42607-33021 for $35 [ https://ebay.to/2W8VEgK ] and (3) that Discount Tire will sell, then physically & electronically install, an aftermarket sensor for about $60 each.

My understanding is that a Japanese company named Pacific Industrial manufactures the sensors for Denso, that in turn sells them to Toyota/Lexus.

eelliiss

Piggybacking off of this thread. I did a search and found a few others, but with no clear resolution.

Dropped my son off at school, and I noticed that the tire pressure light came one. I toggled between screens, and, to my surprise, I had a completely blank screen for the TPMS. I just checked all the pressure. Everything is within spec, so I believe that one or more of the batteries have failed. However, would this cause the screen to go entirely blank? I've tried the reset button. Any thoughts? I would imagine that at least one sensor would work and I'd get at least one reading.

edit: It's a 2010 base model. I have not put on new tires. I did change some settings for the lights, ie. turned off the daytime running lights and I also have the low beams as turning off immediately when the car is shut off as opposed to staying on for 30 seconds. Also something odd to note, my automatic lights stayed on in bright sunlight this morning. I turned them all the way off, then put back to auto, and they stayed off. Strange. Not sure if it's all related, but I thought I'd throw that in there.

DJWLDW

eelliiss

Yes when you lose one sensor the whole screen goes blank on that setting. The same think happened to me on a road trip to Richmond, VA a few weeks ago. All the tires were fine but a battery went out and the screen went blank. Waiting on new sensors mine is also on a 2010 LS 460L which is now over 11 years old.

Dennis

eelliiss

Awesome. That's what I was leaning towards. Appreciate the confirmation.

I hope all is well in Arkansas. it's my home state. Lots of fond memories of Ft. Smith (my hometown) and Fayetteville (college).

DrQuality

I've had that happen sometimes with the headlights set on 'auto.' Such as when I am parked in a dark/shaded area, like a parking garage or whatever, when I first turn the vehicle on. Sometimes they will turn on ... and stay on ... even after driving into sunlight. And yes, if I flip them to 'off' then back to 'auto' they go off and stay off. Doesn't happen if I drive into dark then drive out again, such as driving through a tunnel. Only if I START the vehicle in a dark location. And only sometimes. Apparently, it's just a peculiarity of the sensor logic or something.

DrQuality

The reset button isn't well documented as it could be. All the TPMS reset button really does is reset the psi at which the yellow lights & warning telltales will trigger. It will reset the trigger to a 20% drop in psi from whatever the tire pressure was when you pushed the reset button. Unless the tires are at 33psi or less, then the trigger is set to a 20% drop from 33psi. It does not reset the TPMS system in any other way.

jmcraney

Dr Q, please be reminded that the LS460 TPMS measures and displays Absolute Pressure. Most handheld tire pressure gauges used in the US measure Gauge Pressure. The difference in Gauge Pressure and Absolute pressure. for your location, elevation 2000 ft, is approximately 1 PSI. If you have already considered this in your calculations, please pardon the intrusion.

DrQuality

Thank you for adding that information to the discussion. Actually I was NOT aware of that phenomenon ... until reading about it here recently in some of the other ClubLexus discussion boards ... thank you everyone! My prior vehicle, totalled-out earlier this year, was a 2006 Avalon. And so it did not have any TPMS sensors that became mandated shortly thereafter. And so I had no prior experience with them.

In any case, I specifically stated things like "when all five tires were all sensing" and "if your tires are sensing at" ... hoping readers would understand that I was referring to readings from the TPMS sensors, not from a regular tire gauge.

Because I now know that the readings from a TPMS sensor & an ordinary tire gauge can differ due to design, I just purchased last week (what I think to be) a highly accurate tire gauge ... so I can see & compare what the gauge is reading to what the TPMS sensors are sensing ... and be aware of the difference.

But, again, in the discussion above, the pressure I reported when pushing the TPMS button, the pressure I said triggered the telltales, all those were all TPMS sensor readings from the instrument panel, not from a regular tire gauge.

jmcraney

Dr Q,

Please share with us the details of your "highly accurate tire gauge."

I'm still not clear about how you used the TPMS display to measure your low pressure warning thresholds. The display has 1 PSI resolution. That means that any reading has a + or - 1 PSI uncertainty. Seems like using the display for both measurements would cause an uncertainty of 2 PSI. And you need to keep in mind that you can't set a new threshold if the system is in an alarm state. And you need to keep in mind that the thresholds have hysteresis, so you have to approach them going down. Measuring the thresholds with the the display, or a handheld gauge would be tedious and time consumng.

As for your contention that the warning threshold is 20% instead of 25%, that seems unlikely. The NHTSA TPMS Final Rule says that the threshold will be 25%. I don't believe that Lexus would be noncomplient with that rule.

Here is a link to the TPMS Final Rule: https://www.nhtsa.gov/sites/nhtsa.go...inalrule_6.pdf

It's a long read and little hard for me to understand.

The rule was not rigid about implementation. There was wide variation in implementations by various car manufacturers, and Lexus did theirs quite different from many. With the Lexus implementation you can set your margin over a very wide range, like from 1% to perhaps 35%. Following their directions will get you a 25% margin. I am sure there is a low limit but nothing close to what you indicated.

This is all esoteric and it is unlikely many are interested in this except you and me. We're sort of like "stompin pissants while the elephants are in the corn."

The Lexus TPMS is a highly reliable safety feature when it is set up properly and can be nuisance when it is not.

Don't forget to tell us about your new tire gauge. I have a Moroso 89575 that I am very fond of. It has 0.1 PSI resolution. https://www.summitracing.com/parts/MOR-89575?rrec=true

DrQuality

First, my findings of a telltale trigger floor at 26-27psi appear to be in general agreement with your post at

https://www.clublexus.com/forums/ls-...ml#post5503913

where you said "When I benchmark at 33 PSI, my warning comes on when the display changes from 27 to 26."

I inflated all the tires up to around 35psi. Then I deflated them all, one at a time, bit-by-bit until each tire sensed & read 30psi on the TFT Multi-Information Display, When all five tires sensed/read 30psi on the TFT Multi-Information Display, I then pushed the TPMS initializing/benchmarking/resetting button. Then, starting first with just one tire, I would let a bit of air out, then go check to see if the TPMS 'telltale' low pressure warning & yellow warning lights had triggered. When it did finally trigger, I took note of the psi it was displaying (in yellow) on the TFT Multi-Information Display for the under-inflated tire. Then I re-inflated that tire back above 30psi, so that the TPMS 'telltale' low pressure warning & yellow warning lights cleared off. Then I repeated that process for each tire (including the spare). By this process, the telltales triggered for a displayed value of either 26psi or 27psi for all five of the tires.

Yes I agree and I did realize that. When I said (that some tires triggered at 26psi while others triggered at 27psi) I also said "I attribute that variance to the undocumented method of 'rounding/truncating' being used to display integer psi values."

In reality, a sensor display of 26psi, could be sensing as low as 25.01 or so (if the display is always being rounded up to the next highest integer) or sensing as high as 26.99 or so (if the display is always truncating to the lower integer). Either of those rules would generate a maximum uncertainty of just at 1psi. For example, when truncating, a telltale trigger pressure displaying at 27psi could be truly sensing as low as 27.00psi and then being compared to a benchmarking value being displayed as 30psi when truly sensed at 30.99psi (and being truncated). The displayed difference would be 3psi, but the truly sensed difference would be 3.99psi. So the error/uncertainty would be -0.99psi.

Or it might be rounding in a more traditional way, rounding down to the lower integer until a value of .5 or more where it rounds-up to the higher integer. That rule would also generate a maximum uncertainty of just at 1psi. For example a telltale trigger pressure displaying at 27psi could be truly sensing as high as 27.49 (and rounded down) and then being compared to a benchmarking value being displayed as 30psi when truly sensed at 29.50psi (and rounded up). The displayed difference would be 3psi, but the truly sensed difference would be 2.01psi. So the error/uncertainty would be +0.99psi.

So yes I do agree that the uncertainty of the comparison using the TPMS displayed values can vary as much as +/- 1psi. Said a simpler way, since the TFT Multi-Information Display only displays to the nearest integer, it can’t yield any more accuracy than that.

It might seem that gauging the tire when the TPMS benchmark button is pressed, then gauging again when the telltales trigger, would yield a more accurate answer regarding the difference. But if we gauge the tires at, say, 30psi then press the TPMS button, we still do not know exactly what benchmarking value is being stored, since any rounding/truncating rule might (or might not) end-up being first applied to the sensed value before storing. The same goes for the trigger value. So you really cannot 'dodge' the rounding/truncating issue no matter which way you go. And with gauging, to determine where the TPMS floor 'really is,' you would have to attempt factor-in the error from altitude effect you mentioned. Better just to keep it all 'apples to apples' and compare the benchmark value as seen on the dashboard … to the telltale trigger value as seen on the dashboard … to learn (as best as possible) how the dashboard is designed to handle the difference between the two.

I suppose we could deduce the rounding/truncating rule and factor it into the calculation, by gauging the tires then inflating/deflating them by very small amounts, and noting the effect each iteration has upon the displayed values and the telltale trigger-points and such.

But I wasn't going for all that degree of precision. I was just more interested in finding out if there was a 'floor' on the benchmark value and telltale trigger value. So that if I choose to run the tires at 30psi and benchmark them there, that I would know if the telltale trigger values would (or would not) adjust down in synch.

And from what you said … and what I discovered … the floor on the benchmark is (a displayed value) of 33psi and on the telltales at (a displayed value) of around 26 or 27psi.

Well running the math on the 26psi & 27psi numbers, that you and I seem to agree upon, yields:

33-27=6 & 6/33=18.18%. If we approximately factor-in the maximum uncertainty, 33-26=7 & 7/33=21.21%

33-26=7 & 7/33=21.21%. If we approximately factor-in the maximum uncertainty, 33-25=8 & 8/33=24.24%

So to hit near the 25% number you've noted, the tires would have to always trigger at 26 (not 27) AND always be incorporating the maximum uncertainty/difference. But, as I said, for me, sometimes the tires DID trigger at 27.

Also, you stated at

https://www.clublexus.com/forums/ls-...ml#post5503913

that "On my car for example, when a tire is benchmarked at 40 PSI the alarm is generated when the display changes from 32 to 31." The quick math applied there is

40-32=8 & 8/40=exactly 20% … and 40-31=9 & 9/40=22.5%.

Since some of my own tires triggered at 26 and others at 27, I used the average, 26.5 (that average functioning so as to incorporate an estimate, over the five tires, of any + or – variance due to rounding/truncating) to estimate the actual percentage: 33-26.5=6.5 & 6.5/33=19.70% or, basically, 20%.

If Lexus used 20%, that actually would NOT be non-compliant, it would actually be excessively compliant, in that the tires trigger even before reaching the government-mandated trigger of 25%.

The NHTSA document to which you directed me was incredible as to how it details all the various decisions that needed to be reached as to how exactly all the various functions of the TPMS system should perform!

The document explains, at great length, the logic by which it finalized the threshold at 25% as the best option. It also documents that a 20% threshold was proposed as the initial rule. And pages 39-44 contain an interesting discussion where a number of interested parties (including TireRack, AAA, the Tire Industry Association, even Fairfax County Public Schools) had actually argued for a more stringent threshold, some arguing specifically for the 20% threshold. And it documents that, in fact, one party SUED to try to force a 20% threshold (and lost). On page 46, the NHTSA explained the reason it chose 25% versus 20% was because -- believe it or not – it thought 20% would cost manufacturers more to implement on a cost-per-life-saved basis! The document 'double-downs' on its 25% vs. 20% decision in other places, including page 186, even though it there states that a 20% threshold has 15% greater total benefit than a 25% threshold. While the document finds, it its opinion, that the 25% threshold is optimal, I did not find anything in the document that prohibited a manufacturer from incorporating a more-stringent threshold if it wished. Only that it cannot be LESS-stringent.

Given all that, perhaps Lexus thought it was better to err a bit on the side of caution with a somewhat more-stringent-than-required threshold of 20%.

Well, when I said "highly accurate," I meant more accurate than my cheap pencil gauge … and my Milton Accu-Gage S60X analog gauge that I've had for 12 years and has probably been knocked-out-of-whack by now. I actually saw your recommendation of the digital Moroso gauge at

https://www.clublexus.com/forums/ls-...ml#post5500303

and so I did consider it before buying when I was shopping around. But at Summit Racing [ your link at https://bit.ly/2Wr1xqj ] it was $82 and similar digital Moroso models on Amazon were about the same price. While it might be extremely accurate, that was just a bit more than I wanted to pay for a gauge. I ended up going with a digital Jaco gauge of similar design [ https://amzn.to/3zpOMdO ]. Again, it may not be as accurate as your choice, but it was Amazon-rated at 5-stars over almost 2,000 reviews, it is surely much more accurate than what I had, it also has a 0.1 resolution, has a chuck that many reviewers said was easy-to-use, and it was only about $27.

Best wishes,

jmcraney

Dr Q,

Good choice on the new gauge. I think many fail to appreciate the need for higher resolution. The one you picked should do nicely and at a reasonable price. I hope people are paying attention. Those wanting to get the most from their TPMS, and tires, need to be using a gauge with 0.1 PSI, or better, resolution. And they should pick a gauge with a bleeder valve, like the one you selected.