hardimen

Hello everybody. I recently replaced one of my tires with the spare tire which is brand new. The old tires are at 5/32" and one had a flat and the shop said it was not repairable. So now, all tires including the spare is set to 33psi. I drive to work about 25 miles and around the 20 mile mark, my Low Pressure warning light comes on. I reset it and then the next 20+ miles on the freeway, it comes back. I don't want to replace tires just yet, I think I still have around 5-10,000 on them. I believe these brand of tires are rated around 30-40k and it has less than 25K on them.

All tires are Dunlop SP5000 P245/45R18 including the spare. The spare is in the front left side. Is there anything I can do to make the warning not come back again without replacing all 4 tires? Should I experiment with changing the tire pressure on the spare to (higher or lower)?

By the way, the warning light did not use to show up before I used the spare tire.

Thanks.

Jabberwock

The TPWS on the LS430 does not measure actual tire pressure, instead it works by measuring the outside diameter of each tire and comparing that with the others. It does this by counting rotations of each wheel and comparing rotations to the other wheels to see if they are the same as other wheels. The sensor that measures each wheel's rotation is also part of the ABS system.

So use the manual to actually reset the system - a specific procedure is required to reset the system versus just resetting the warning. Its in your manual. If the reset does not work and the system throws another warning code, it may be because the new spare is larger in diameter than the other more worn tires.

You could theoretically try to compensate by running a 1-2 less in the new tire, but that would mean driving tires with unequal pressures - not something I would do.

hardimen

Thank you sir. I did not know about the reset system. I will read my manual again.

Sentinel

I could never get the system to work with a spare. even after I reset it.

CarGuy89

I'm experiencing a similar problem. I just replaced all 4 tires with new Michelin Primacy MXV4s (phenomenally good tires btw) and my car's been throwing low tire warnings a lot. I thought it was b/c it was getting a bit cold lately but it did it today on a warm sunny day I checked the pressures and they were appropriate with +/- 1-2 psi between all of them. Should I just pump them up higher to compensate for the colder weather?

hardimen

ok, I reset the system and crossing my fingers. I'll give you an update soon.

diagtime

when you guys say reset the system.....what are you doing? just hitting the button once turns the light off. you need to hit it again until the message "Pressure Initial" comes up in the trip info screen under the Tach

CarGuy89

Oh I was not aware of this, all I have been doing is holding down reset until the message is gone. I'm assuming this recalibrates the system? Thanks for this piece of info

Jabberwock

Usually its because you did not "initialize" the system but instead you "reset" it. There is a difference and its buried in the details of the manual : ( so you have to look it up and follow the process exactly. And make sure your tires are corcetly inflated and all the same when you do the initialize process - because thats the "base" level that is set for comparisons by the system - if the tires are off when you initialize it will drive you crazy.

The system works by detecting rotation size differences in tire from its "initialized setting" . So any time you change your tires or you change pressures on your tires from the "initialized" setting the system will detect a difference (assuming pressure diff causes a size diff) and throw a code.

Its a fairly primitive system - it has no idea what the tires pressures actually are. It can't detect that a tire has lost pressure (and therefore size) unless the car is in motion and wheels are rotating. It actually can't detect which tire has the problem because 3 of the tires may gave been overfilled which will produce the same warning code. And if you put on a smaller temp tire that has correct pressure it will throw a code just based on minor size difference. And of course it certainly can't detect that your spare in the trunk has gone flat. But its better than nothing but its amazing how few people actually understand how these first TPWS system actually work - even service managers at the dealer are sometimes clueless.

CarGuy89

Excellent explanation Jabberwock! Thanks

hardimen

I initialized the system and it seems to be working. No more low pressure warning so far... thanks!

AlexusAnja

If by some chance all four tires are losing pressure at same rate, you could be 25psi on all 4 and system.would not trigger because they are all rotating at same rate so system thinks everything is fine. Check your tires ever so often still because I had 26 psi on all 4 when I got LS.

john339

As an aside, when we bought our LS430 the tires were at 35 psi.
After changing them down to 30 the ride is so much smoother.

diagtime

it not only works on wheel speed, it also uses the frequency changes from the abs sensors. even extended drives now a gravel road can set it off. It's called an indirect tire pressure monitoring system. nowhere near as affective as the Direct TPMS that cars have now.....but it's better than nothing