If one or more of the TPMS sensors within the wheels are bad, the TPMS light will flash at each vehicle start, then turn and stay on steady. My tire dealer used some type of scanner/sensor and determined that three of the four sensors are bad. (there is no TPMS sensor in the temporary spare, one in the regular wheels and tires).These are not cheap to replace, even by eBay, and to do so requires removing the tire from the wheel to get at the sensors, which are essentially located within the tire below the valve stem. I am choosing to ignore the light, keep a tire gauge in the door pocket, and check the air pressures in all my tires the old-fashioned way about once a week.