A couple weeks ago in my '00 LeSabre, the "Check tire pressures" warning message came up. I checked them all, and sure enough my right rear tire was about 10-15 psi low. I topped it off with plans to keep an eye on the air loss, and figured the system was working properly. Problem is that the warning message has never gone away, even though the tire pressures are all fine (I've checked them repeatedly). I suppose I should disconnect the battery to reset? If the false warning comes back, I guess I have a by TPMS sensor but I don't know how to determine which one on this vehicle.

Second issue, maybe related and maybe not. A few days ago, that same RR tire was almost completely flat after the car sat overnight. I overfilled it to 40 psi (instead of usual 34) and let the car sit for 3 days. The tire lost no air whatsoever... still remained fine after driving 20-30 miles and checking again. I don't see a nail/screw or anything else in the tread. Is there anything else mechanical (a faulty valve stem?) that could cause a one-time air loss, or did someone play a prank on me and deflate my tire?

Essentially, that vehicle monitors discrepancies in wheel speeds to determine if a tire is low. Usually when you check and correct tire pressure, you need to reset the system with the reset button.

Also, valve stem/cores can be intermittent in nature, or even corrosion on the rim too. Hoodlums aren't out of the question either but it'* still too soon to tell.

Ah... I had been pushing 'Reset' to clear the code at each engine startup, but it never occurred to me to seek out the more permanent reset option. I just went out there, and scrolled through the "Gauge" button options until Tire Status came up... held down the 'Reset' for 5 seconds, and the status returned to normal. Thanks for the reminder/tip!