It could be a leak. The wheels have sensors that are wireless. They save power by not transmitting until they sense a specific speed. They also don't constantly transmit. They can last a number of years, but they eventually will need to be replaced. They are often not very accurate.

First check the tire pressure. If the pressure is actually low, then fix the tire.

If you are running a tire pressure that is near the threshold that triggers the warning, then you might find the warning happens when it is cool, but doesn't happen when it is hot. Factor in that the pressure sensors are not that accurate and you can get false warnings.

If the tire pressure is not low, then you have two options.

1. Have the tire taken off to replace the pressure sensor
2. Wait until the tires need to be replaced to have both the tire and the sensor replaced. This will save you some money, but you will have to ignore the warning as long as you verified the tire pressure.