Warning lights
Tire pressure light: steady, flashing, and what each means
The horseshoe-shaped light with an exclamation mark is the tire pressure monitoring system, required on new cars and light trucks since 2007. It has two messages, and they look different.
Can I keep driving with this light on?
Tire pressure light: on and steady
Moderate: fix within weeks
At least one tire is well under its placard pressure: check all four before driving far.
- Look at each tire for a puncture or a flat.
- Check the cold pressures against the door-jamb placard and inflate.
- Drive a few miles: the light should go off once pressures are restored.
49 CFR 571.138 S4.2: lights within 20 minutes once a tire is 25 percent below the placard pressure (or the minimum activation pressure); S4.4: a system fault flashes 60 to 90 seconds at start, then stays on. Your owner's manual prevails for your car.
The tire pressure light is governed by Federal Motor Vehicle Safety Standard 138 (49 CFR 571.138). On a vehicle that has the system, the yellow low-pressure telltale must come on within 20 minutes of driving once one or more tires is 25 percent or more below the cold inflation pressure on the vehicle's placard, or below a minimum activation pressure for the tire type, whichever is higher; for standard P-metric tires that minimum is 20 psi. A steady light therefore means at least one tire is significantly underinflated. A light that flashes for about one to one and a half minutes at start-up and then stays on means something else: the system itself has a fault, such as a dead sensor battery or a sensor missing from a new wheel, and it may not warn you of low pressure. In both cases, check the pressures with a gauge when the tires are cold and inflate them to the placard, not the number on the tire.
At what pressure does your tire light come on?
The light must be on at or below
26.3 psi
| 25% below placard | 26.3 psi |
| Minimum activation pressure | 20 psi |
| Rule that applies | 25% below placard |
49 CFR 571.138 S4.2 and Table 1: within 20 minutes of driving once a tire is that low. Many systems warn earlier.
Codes, rules and labor data checked by Radif Partners · Editorial policy · Method and sources
The pressure that turns the light on
The rule sets the trigger at 25 percent below the placard pressure, with a floor for each tire type. For a car whose placard says 35 psi, 25 percent below is about 26 psi; for a light truck tire whose placard says 40 psi but whose load range sets a floor of 35, the floor applies instead. The calculator on this page applies the rule to your placard and tire type. A tire 25 percent low has already lost a lot of air: the light is a late warning, not an early one, and a monthly check with a gauge catches pressure loss sooner.
What to do when it comes on
- If the car pulls, thumps or a tire looks flat, slow down and stop somewhere safe; driving on a flat damages the tire and the wheel.
- Otherwise, drive gently to the nearest air pump and check all four tires, and the spare if it is monitored.
- Inflate to the placard pressure. If the tires are warm, add about 3 psi and recheck later when cold.
- If one tire keeps losing air, have it inspected for a nail or a leaking valve.
When it flashes
The standard requires the system to detect its own faults and warn by flashing the telltale for 60 to 90 seconds after each start, then keeping it lit, so that a driver knows the low-pressure warning may not work. It can share the low-pressure telltale or use a separate "TPMS" lamp; the symbols are set by FMVSS 101. Common causes are a sensor battery at the end of its life, a damaged sensor, a sensor not relearned after a tire rotation, or wheels without sensors. A tire shop can scan each sensor and tell you which.
Direct and indirect systems
Some cars measure pressure with a sensor in each wheel; others infer it from wheel speed, since an underinflated tire turns slightly faster. Indirect systems need a reset after inflating, using a button or a menu, which the owner's manual describes. Both must meet the same warning requirements. The symbol finder shows the other yellow telltales for comparison.