Low tire pressure, but no leak

I have a 2005 Toyota Highlander. Ever since I got 4 new tires (~1 year ago), my low pressure light goes on about once every 6 weeks. Each time, there is at least one tire that’s dropped about 2 lbs below recommended psi. Had it to the dealer (where I purchased the tires) and they told me there’s no leak in any of the tires; that the low psi is because of fluctuation in the weather temps and subsequent fluctuation in tire pressure. I’ve never had this issue on any other car before. Are they pulling my chain b/c they don’t want to replace bad tires or is this a legit reason?

First, read these articles:


Is this happening on a specific tire or more than one?

Did you buy the same brand of tire that came on the Highlander? Different brands and makes have different air retention properties. I have a habit of checking all my tire pressures every 2-4 weeks, and always notice a 2 to 3 psi drop in some of the tires. It is the nature of tires to seep some air as they work. Some makes of tire just seem to seep more than others.

bead leak or valve stem seal. 98% of time. have tire remounted with sealer on bead area. change valve stem.

I would take it back to where you bought the tires and have them check to see if they accidently damage the sensor in there.

If your TPMS on your 2005 Highlander is like the TPMS on my 2005 Scion, and uses the wheel speed sensors rather than pressure monitors behind the valves, the problem is one of reinitializing the system. Every time I get new tires I have to do this, Reinitializing isn’t the same as resetting the system, rather it establishes a whole new baseline. Resetting the system requires just pushing the reset button in, but reinitializing requires a whole protocol with putting the key in the ON position (not running) and holding the button in until the TPMS light flashes three times.

Look carefully in your owner’s manual and see if yours has the protocol. Or just try it. You’ve nothing to lose.

"Each time, there is at least one tire that's dropped about 2 lbs below recommended psi."

The TPMS is working. Tires lose pressure over time, all tires do. You just never noticed this before because you didn’t have TPMS. When you have the tires aired up, I would suggest that you go a couple of pounds over the recommendation on the placard. If the placard calls for 32 psi, put in 35.

This should keep your tires near spec for the duration between oil changes, when the tires are usually checked and aired up again.

BTW, if one tire is always responsible for triggering the TPMS, that tire has a slow leak. But to lose 2 psi in 6 weeks would be a leak that is virtually undetectable, but if it has one, I would suspect the valve core is defective or just not tight. Your tire dealer should first try to tighten the core. It takes almost no time to check that.

Tho OP said the tires are actually low so no problem with the TPMS. Its physics, pressure goes down with cold air and up with warm air.

As has been said here before, the pressure gets lower in cold weather and higher in warmer weather. However if only one tire is low, then you have a leak.

TSM (The same mountainbike) Has Given Good Advice.
Toyota Gave Special Attention To Your 05 Highlander When They Felt The Need To Publish A TSB (Technical Service Bulletin) To Help Their Technicians With 2004 -2005 Highlander TPMS Re-Initialization.

Link to TSB PG005-04


Two lbs every 6 weeks is a leak.
The tire inner liner is made from butyl rubber. If the tire is intact, it’s not leaking out the tire. If you want to solve the problem, here’s what I suggest:

Have the tire shop dismount the tire from the rim.
Look carefully for foriegn objects puncturing the inner liner. You’d be surprised how often this is a problem that can’t be easily seen from the outside and causes really slow leaks.
No punctures? have them clean both rim bead surfaces with a rotary type scotch brite pad to remove any debris and clean up any clearcoat issues caused by corrosion (often the result of the clearcoat being compromised by crimp on weights).
Install new valve stem.
Apply bead sealer to both bead surfaces and reinstall tire to rim.
Balance and install on vehicle.

See if the leaking has stopped.
If not, is this an aluminum wheel? Suspect porous wheel. Dismount tire and apply sealer to wheel inner areas and reinstall tire using above mitigations.