I just put mounted snows on our '10 ES350.
There are NO TPMS sensors on the wheels.
Spare with sensor is still in the trunk.

I figured I'd be looking at the Yellow TPMS Warning light on the dash for the winter. Today the light WENT OUT.

The symbol illuminates when the ignition is turned and the system self tests and then goes out.

Anyone know what is going on? So far my local dealer has no answer.

Maybe the programming is specific. That is, if there are no individual sensors to report to the "head unit", then it assumes there are no problems. When the sensors report a certain psi number and it does not jive with the variance number (say 26psi - 45 psi), then the light goes on. With your spare tire reporting, then the system assumes everything is OK. No report of the other four wheels = no problem. Just a long shot theory.

Interesting thought, but my guess is unlkely.
The Feds want a system that works. The system can't be inactivated (easily) by the owner.
And what happens if a battery dies in a sensor? If the light goes out you'll assume it is a system glitch that recovered and all is well.

I have put summer tires and wheels (with no sensors) on for the last 3 years. It always shows no fault for some time, usually 2 or 3 months. Eventually it will show a fault and once it does, there is no way to get rid of the light until I put the original tires and wheels (with sensors) back on. I always thought it was odd. I concluded the same as gasarno, that it only shows a fault if a sensor reports a fault. No sensor - no fault. Eventually something cause the system to poll the sensors and at that point it detects the error. Maybe the spare reports a change in pressure that the system tries to compare to the other tires? All just speculation on my part.

Pete

Any chance your mounted summer tires are stored near your car? The car could be reading the sensors from the original tires/wheels

WOW. jeffs3820 is thinking. Great observation.

The summer tires are stored about 30 feet away from the car.

I don't think that would do it. The first year after the dash light came on, I tried an experiment to see if I could reset the light by rolling the mounted tires with the sensors (properly inflated) and leaning them against the mounted wheel at each tire position. I still could not reset the light. It seems they have to be mounted on the car, or at least with the car moving before the sensors are detected.

Pete

I think Pete is probably right - the TPMS only checks at some fixed interval, miles or minutes, so having the tires in the garage probably would not have any effect. For example, if you walk out some morning and find that a tire is completely flat the TPMS warning would not come on if you started but did not drive the car. Having all four tires in the trunk might might fool the system, I don't know.

Dave Mac

I had real problems with mine when I changed to a set of winter tires, the warning light did not intially come on, then with every bump I hit on the road. The resetting was a problem too, did not always work. The trick I found was if the tire pressure was 35lbs+ then when it hit the bumps it did not alway show the warning light. I would like to know what logic it follows .

Anyone know if it is possible to purchase the device to reset the TPMS on your vehicle?

Mystery is over. After a couple hundred miles the light came back on.
Actrually it came back on the day I was schgeduled to have sensors installed in the aftermarket rims.