Wife bought a 2005 LS430 a little over a week ago. This morning was the first chance I've had to check air pressure in the tires. 18" tires----33psi.

Rear tires checked at 21psi, front--24psi and the spare---18psi. I rarely check spare tires-----I think from now own, I'll check spares more often.

 

The 05 LS430 doesn't use the TPMS System that Lexus is using today. Your 05 works with the vehicle's ABS braking system to determine the RPM's of each wheel. If the RPM's increase on one of the wheels, it's a signal to the system that the air is low on that wheel. With this type of system, the air pressure of your spare tire in the trunk, isn't being monitored, since its not mounted / spinning on the vehicle. This type of system is called an "Indirect System".

The TPMS Lexus uses now is considered a "Direct System". It has a pressure sensing valve inside each rim that is incorporated into the valve stem. This includes the spare. With the direct system, if a tire, including the spare starts to lose air, the low pressure warning light comes up on the instrument cluster.

My wife's 08 ES350 and my 08 GX470 both have the newer system. My 05 LS430 has the system like yours...

 

I check the spare once a year at least and add air as necessary. Im surprised the system did not throw a low air warning considering it was in the lower 20's. Make sure you initialize the system once you refill to keep this from reoccurring.

 

I, for one, cannot stand the "low air warning systems". I do not need an idiot light/beep to advise me when a tire is low. My 2006 Tundra DC has the TPMS system----bought some Tundra spoked wheels to replace the "cheap" steel wheels that came on the truck---the TPMS valve stems wouldn't fit the new Toyota wheels so I sold them on eBay. The TPMS warning light stays "on" which I could care less.

 

This is preferable to me, as the new system relies on a battery powered transmitter inside the valve stem device. If the battery goes low (and we know lithium batteries only last a max of 5 yrs, and all batteries discharge faster in high temps), I assume you have to dismount the tire to replace it? Ideally, a tire pressure monitor system should merely display the pressure of each tire (say, via the display switch on the steering wheel) and not display any low pressure warning unless, say, under an aburdingly low value like 15-20 psi is detected. If the pressure drops from 33psi to 31psi overnight due to abnormally cold weather, I don't want my warning to go off. What are you gonna do anyways? You still have to drive to a gas station to air up, unless you plan to break out the compressor at 6am on a weekday before the commute.

 

The new direct system only triggers an alert if one tire varies from the others by X number of pounds (I'm not sure what the variation is). So if all your tires go down or up together because of a variation in temperature, I don't think that would signal a warning.

I think our system is just fine except for the fact that it doesn't account for the air in the spare, which could leave you stranded (or more inconvenienced anyways) if you don't check it regularly.

 

To each his own.... I'm glad the new vehicles have this system. One day you may learn to appreciate the idiot light.

My wife once called me to complain that the steering on her car was "tight"??? The car was hard to turn.... She calls me a few minutes later from a gas station to tell me that the guy next to her asked her about the flat tire. She had traveled about 5 miles with a flat tire.

My first Honda Pilot didn't have TPMS. I was going down the highway at 75 mph, had the radio up loud and heard a hmmm.. I turned the radio down and then recognized a strange noise. I pulled off the highway just as the tire started coming apart..... It didn't take long to go from low tire pressure to shredded tire..... An idiot light would have been appreciated.

 

Like I said, you just need warning for an absurdingly low tire pressure (like 15lbs low), not slightly low (2 lbs low).