TPMS Light On? Solid vs Flashing, and What to Do Next

What the TPMS light is actually telling you

The yellow horseshoe with an exclamation point is your tire pressure monitoring system, or TPMS. It became standard equipment because of a federal rule: passenger cars, SUVs, trucks and buses with a gross vehicle weight rating of 10,000 lb or less built from September 1, 2007 onward must have one.

The rule, FMVSS No. 138, also sets when the light has to come on. The low-pressure warning must light up when a tire is 25 percent or more below the vehicle maker's recommended cold pressure (or a minimum level the standard sets, whichever is higher), within 20 minutes of reaching that point.

That 25 percent figure is the key to everything below. The light isn't a gentle reminder. By the time it's on, a tire is already well down.

There are two ways the light behaves, and they mean different things. Pick what your dash is doing:

Solid light: at least one tire is low

A light that comes on and stays on, with no flashing at startup, is the low-pressure warning.

What to do:

1. Don't ignore it until the weekend. At the first practical stop, check all four tires with a gauge.
2. Compare against the placard, not the sidewall. Your vehicle's recommended pressure is on the Tire and Loading Information label, usually on the driver's door edge or door post, and in the owner's manual. The number molded on the tire is a maximum, not a target.
3. Know whether the tires are cold. NHTSA defines cold as parked for at least three hours. NHTSA notes that pressure normally rises as tires warm, so a reading right after a drive on I-595 can be higher than the cold number.
4. Add air to the placard pressure. If the tires are warm, don't let air out to hit the placard number; NHTSA's advice is to recheck when they're cold before adjusting down.
5. Watch that tire. If the light comes back within days, or one tire keeps reading low, you likely have a leak. Have it inspected.

A slow leak isn't always a visible nail, so let a technician find the source. Extreme Tires repairs tires with a combination patch-plug from the inside after dismounting and inspecting them, at the Sunrise shop or by mobile van in the local install area.

Flashing, then solid: the system has a fault

This is the one people misread. Under FMVSS No. 138, when the system detects a malfunction, the light must:

• flash for at least 60 seconds but no longer than 90 seconds after you turn the ignition on, then
• stay on continuously as long as the malfunction exists,
• and repeat that sequence at every startup until the problem is fixed.

So a flashing-then-solid light doesn't mean "very low tire." It means the system can't do its job. Your pressures could be right, or they could be low and the system can't tell you.

Until it's fixed, you're driving without the warning. Check your pressures with a gauge in the meantime, and have the system diagnosed. A technician with a TPMS scan tool can read which sensor isn't reporting.

Extreme Tires' TPMS service covers a sensor scan and battery health check, sensor replacement where needed, and relearn and programming to the vehicle, in the shop or from the mobile van.

Came on during a cool morning?

South Florida doesn't get much cold, but a front does bring the occasional cool morning.

NHTSA's explanation is simple: as the outside temperature drops, so does tire inflation pressure. A tire that was already running a little low can cross the 25 percent line overnight and trip the light at 7 a.m. Then the day warms up, the pressure rises and the light may go out on its own.

The light going out doesn't mean the problem went away. The tire was low enough to trigger a warning, so set all four to the placard pressure, cold, before the afternoon heat hides it again. Our guide to tire pressure and temperature shows how much a front can move the reading.

Came on after new tires or a rotation?

A light that shows up right after tire work can point to the sensors rather than the air. Depending on the vehicle, sensors may need to be reset or relearned after they move positions or are replaced. Your owner's manual lists the procedure for your car.

A tire installation at Extreme Tires includes a TPMS reset where the vehicle has it. If the light appears after the fact, call (954) 773-1896 and ask.

Light off doesn't mean pressure is right

Here's the part most drivers miss. The TPMS warning is designed to come on at a significant pressure loss, not a small one. A tire can be 15 or 20 percent low with the dash completely dark.

The regulation itself says it: TPMS is not a substitute for proper tire maintenance, and keeping correct pressure is the driver's job even when the light hasn't come on. NHTSA's guidance is to check pressure with a gauge at least once a month, spare included, with the tires cold.

Quick reference

Want the full routine? Our guide to checking tire pressure walks through it, and the Do I Need Tires Yet? check covers tread and age while you're down there.