Solid light: low pressure
On many direct TPMS systems, a light that comes on and stays on means one or more tires is well below the recommended pressure (often around 20% to 25% low, though the threshold varies by vehicle). Check all four with a gauge when the tires are cold and inflate them to the figure on the driver's door placard. If the light comes back within days, there's likely a slow leak, often a nail or a leaking valve that flat tire repair can fix.
Flashing, then solid: a system fault
On many direct TPMS systems, a light that flashes for about a minute at start-up and then stays on signals a problem with the system rather than the pressure: a sensor with a dead battery, a damaged sensor, or wheels the car doesn't recognize. Consult your owner's manual, as diagnostic alerts vary across makes.
Why it comes on after a tire change
A fault warning can appear after a tire or wheel change if the relearn or reset procedure isn't done, and that procedure depends on the vehicle. If your winter wheels have their own sensors, many vehicles need a relearn so the car recognizes them; if they have none, a direct system will usually warn all season. Both are handled at a changeover.
Why it comes on on cold mornings
Air pressure drops roughly 1 psi for every 5–6 °C the temperature falls, so the first cold snap of fall turns on a lot of lights. Top up to the placard pressure; the light usually goes out after a short drive. Check again monthly through winter.
Direct vs indirect TPMS
Direct systems use a pressure sensor inside each wheel, usually on the valve, and report actual pressure. Indirect systems have no sensors in the wheels; they use the anti-lock brake wheel-speed sensors to spot a tire turning faster than the others, which happens when it's low.
The two behave differently. An indirect system usually needs a reset after inflating or changing tires, and may not catch all four tires losing air together. Your owner's manual says which one you have and how to reset it.
Sensor batteries
Most direct TPMS sensors have a sealed battery that typically lasts around 7 to 10 years, depending on sensor model and annual mileage. Sensors installed at the same time often fail around the same time.
Can I keep driving?
With a solid light, check and correct the pressure promptly; driving on severely underinflated rubber damages the internal casing and can make the tire unrepairable. With a flashing light, the tires may be fine, but you've lost the warning system, so check pressures manually until it's fixed.
