TPMS Light On: What It Means and What to Do

What is the difference between a solid and a flashing TPMS light?

On most vehicles, a solid light means at least one tire is low on pressure. A light that flashes for a short time when you start the car and then stays on usually points to a fault in the monitoring system itself, such as a sensor that is not reporting. Exact behavior varies, so your owner's manual is the reference for your car.

There are two common designs. A direct system has a pressure sensor in each wheel that reports to the car. An indirect system has no pressure sensors and instead compares wheel speeds from the ABS sensors, because a softer tire rolls at a slightly different rate.

Why does the light come on during the first cold mornings?

Air contracts as it cools, so tire pressure falls when the temperature drops. A tire that was fine in warm weather can fall below the threshold on the first cold morning, and the light comes on even though nothing is leaking.

Can I just add air and keep driving?

Adding air to the recommended pressure is the right first step when the light is solid. After that, the light may go out on its own after a short drive, or your car may have a reset procedure that is described in the manual.

• If it comes back within days: a tire may have a slow leak from a nail, a leaking valve stem or a bead leak at the rim.
• If only one tire keeps dropping: that one needs to be inspected, not just refilled.
• If the light flashes and then stays on: the system may have a sensor problem, and adding air will not clear it.
• If a tire looks visibly flat: do not drive on it. Driving on a very low tire can damage the tire beyond repair.

How does low tire pressure affect braking and ABS?

The tire is the only part of the car that touches the road, so every braking force passes through its contact patch. An under-inflated tire flexes more, the shape of its contact patch changes, and it builds more heat. That can reduce grip and lengthen stopping distance, especially in wet or cold conditions.

ABS releases and reapplies brake pressure based on wheel speed. It works best when each tire grips predictably, and uneven pressures from one side to the other can make braking feel uneven. In an indirect TPMS car, the same wheel-speed sensors serve both systems. If the light is on and the brakes feel different, a technician can check tire pressures and look over the brakes in the same visit.