SW17LS

mckellyb

Maybe it comes from years of owning trucks and other not-exactly-comfy vehicles, but the ride is still great for me at 35 or 40.

DrQuality

According to the (2007 Lexus LS460) Owner's Manual, page 598, the TPMS benchmarking must be (re-)initialized after a battery disconnect.

jmcraney

Thank you for pointing that out. You are right and my comment was wrong. The manual does say that benchmarking is required after the battery is disconnected and reconnected, or if the battery fully is discharged and recharged in place. However, I think, but I don't know for sure, that all 5 benchmarks are defaulted to 33 PSI when the battery is disconnected and reconnected. So, for those of us that use 33, I think that we would not know the difference. I never hear people complaining about TPMS problems after they replace their battery. I have pointed out correctly, several times in this forum, the need to benchmark the TPMS each time after the battery is disconnected and reconnected. This is a good place to remind those with cars that have the TPMS localization feature, 2012 and newer I believe, that the TPMS needs to be benchmarked if the tires are rotated.

DrQuality

Thank you very much for sharing this information; it has already proved to be quite useful.

Later today I will experience a battery disconnect; I am having the clockspring behind the steering wheel and its air bag replaced. But the Vegas heat is not really going to allow me to push the TPMS button right after the re-connection; they are currently set at about 31-32psi when absolutely cold in order to allow them to stay under 39-40psi when at their hottest. And right now, in Vegas, they are getting hot and staying hot very easily. They'll be hotter even when the mechanic is done because the temperature is expected to be 110° by the time he is.

Based upon your information, however, it seems I can just run the vehicle after the re-connection without pushing the TPMS button ... until I observe all the tires right at 33psi, then I can stop and push the button then. Best wishes ...

jmcraney

If I am correct about the benchmark defaulting to 33 PSI, for all five tires, when the car's battery is disconnected and reconnected, then you would not need to benchmark again (press the button) if you plan to use 33 PSI as your benchmark. A benchmark of 33 PSI sets the low-pressure warning threshold to 24.75 PSI (25% margin). All five benchmarks are independently adjustable. Ideally you would like for your tires to be inflated to 33 PSI in the morning, before your car is driven. To keep that cold pressure your tires have to be seasonally adjusted as their pressures vary as a function of ambient temperature. You would need to add air as the seasons cool and let air out as the seasons warm. I watch my display when I start the car in the morning and if I see the pressure is not near 33 PSI then I get my high resolution gauge and inflator out and make an adjustment. Of course if you have some unconventional tire situation or personal preference your car's TPMS can accommodate lots of variation. As for my spare, I benchmark it at 33 PSI and then inflate it to 40 PSI and leave it alone until I see the startup pressure falling below 33 PSI, and that avoids having to uncover the spare to adjust the pressure.

I could be wrong about the default. The safest thing to do is benchmark all your tires at 33 PSI, using an accurate, high resolution gauge.

DrQuality

I concur with AceVA & jmcraney as above.

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.