An amber horseshoe with an exclamation point. At least one tire is 25 percent or more below its recommended pressure — find an air pump.
LowShort trips only$0–$250 typical repair
Diagnostic summary
Problem
Tire Pressure Warning Light (TPMS)
Severity
LowAddress at your convenience
Can you drive?
Short trips only
A tire 25 percent below spec flexes past what its sidewall was designed for, and that flexing generates heat. Sustained highway speed on a badly underinflated tire is how sidewalls delaminate and blow out. It also costs a few percent of fuel economy and wears the outer shoulders of the tread away. A short, slow drive to an air pump is fine. Continuing a 300-mile highway trip on an unresolved light is not — and if the tire keeps going down after you fill it, the puncture needs repairing before the next long drive.
Typical repair
$0–$250
Lamp colour
amber
Common causes
Cold weather dropping pressure, Slow leak from a nail or screw, Corroded valve stem or leaking sensor seal
What the light means
Since model year 2008, US federal rule FMVSS 138 has required every new light vehicle to warn the driver when any tire falls 25 percent or more below the vehicle's recommended cold inflation pressure. On a car placarded at 35 psi, that threshold is about 26 psi. Direct systems use a battery-powered sensor inside each wheel that radios its actual pressure; indirect systems infer it from wheel speed, because an underinflated tire has a smaller rolling radius and turns faster. Either way, this is a low-pressure warning, not a puncture detector and not a tire condition monitor. It says nothing about tread depth, sidewall damage or a nail that has not started leaking yet, and by design it stays dark while your tires are up to five or six psi low.
Flashing vs steady
A lamp that flashes for 60 to 90 seconds at startup and then stays solid is not reporting low pressure at all. It means the TPMS system itself has faulted — most often a sensor whose internal battery has died after 7 to 10 years, a sensor missing after a tire change, or a new set of wheels that was never relearned to the vehicle. The important consequence: while it is flashing that way, the system cannot warn you about a genuinely low tire, so you are back to checking with a gauge.
What to do right now
1Look at all four tires as you walk up to the car. One visibly squatting or bulging at the sidewall means do not drive on it — use the spare or call for a tow.
2If nothing looks obviously flat, drive gently to the nearest gas station air pump. Stay under 50 mph, avoid hard cornering, and keep the trip short.
3Find the placard sticker in the driver's door jamb. That number is your target — not the number molded into the tire sidewall, which is the tire's maximum, not its recommendation.
4Gauge all four tires plus the spare and set every one to the placard pressure. Tires read a few psi high once they have been driven on, so set them cold when you can.
5If one tire reads far lower than the other three, or it is low again within a day or two, you have a leak. Look for a nail head in the tread and get it inspected.
Why it comes on
1
Cold weather dropping pressure
Very common
Air pressure falls roughly 1 psi for every 10°F drop in temperature. The first genuinely cold morning of autumn lights up TPMS lamps across the country, and the reading recovers a psi or two as the tires warm up on the drive.
How to spot it
The lamp appeared on a cold morning, all four tires read within a psi or two of each other, and the light sometimes goes out after 20 minutes of driving.
The fix
Set all four tires to the door placard pressure with a gauge, ideally before driving while they are still cold.
$0–$5•DIY friendly
2
Slow leak from a nail or screw
Very common
A road fastener in the tread often seals itself well enough to leak only a few psi a week rather than going flat. That is exactly why the tire looks fine and the lamp keeps coming back after you fill it.
How to spot it
One specific tire is consistently 4 to 8 psi below the others every time you check, and spraying soapy water on the tread raises bubbles at one spot.
The fix
A proper interior patch-plug combination repair with the tire dismounted. External plugs alone are a temporary measure, not a repair.
$25–$50•Shop recommended
3
Corroded valve stem or leaking sensor seal
Common
Direct TPMS sensors are usually attached to an aluminum valve stem with a rubber grommet and a nut. In salt states, galvanic corrosion between the aluminum stem and the steel valve core eats the stem from the inside, and the grommet hardens and leaks where it seals to the wheel.
How to spot it
Soapy water bubbles at the base of the valve stem rather than in the tread, on a vehicle more than six years old.
The fix
Replace the valve stem service kit — grommet, nut, core and cap — which is standard practice whenever the tire is dismounted.
$60–$250•Shop recommended
4
Dead TPMS sensor battery
Common
Each direct sensor contains a sealed lithium cell that cannot be replaced separately, and it lasts roughly 7 to 10 years. When it dies, the module loses that wheel entirely and reports a system fault rather than a pressure problem.
How to spot it
The lamp flashes at startup then goes solid, and the tire pressure display shows dashes for one wheel while the other three read normally.
The fix
Replace the sensor and run the vehicle's relearn procedure. Replacing all four at once on an older car avoids repeat visits.
$60–$250 per wheel•Shop recommended
5
Sensors never relearned after tire or wheel service
Occasional
The module has to be told which sensor ID belongs to which corner. New tires, a seasonal wheel swap, or a rotation on vehicles that track position all require a relearn, and it gets skipped constantly at quick-service shops.
How to spot it
The lamp appeared immediately after new tires, a rotation, or putting winter wheels on, with all four pressures correct on a gauge.
The fix
Run the relearn with a TPMS tool — a few minutes of work at any tire shop.
$20–$80•Shop recommended
Repairs & cost
Inflate to placard pressure and reset
The most common fix by a wide margin. Air is free or a dollar at most gas stations, and most vehicles extinguish the lamp on their own within a few minutes of driving once pressure is correct.
$0–$20DIY friendly0.3 hrs labor
Puncture repair
The tire comes off the wheel, the injury is inspected from inside, and a combination patch-plug seals both the tread and the inner liner. Punctures in the sidewall or shoulder cannot be repaired safely and require a new tire.
$25–$50Shop recommended0.5 hrs labor
TPMS sensor replacement with relearn
A new sensor mounted to the wheel, the tire remounted and balanced, and the sensor ID relearned to the vehicle. Programmable universal sensors are cheaper than OE parts and work on most vehicles.
$60–$250 per wheelShop recommended0.6 hrs labor
Valve stem service kits, all four wheels
Fresh grommets, nuts, cores and caps on all four sensors with mount and balance. Worth bundling with any tire replacement on a vehicle past six years old.
$80–$200 all fourShop recommended1 hr labor
What the TPMS light does in cold weather
Air pressure and temperature are directly linked, so a tire you set correctly in August genuinely reads lower in November without losing a molecule of air. The rule of thumb is about 1 psi for every 10°F change, and it catches out drivers every single autumn.
Ambient temperature
Approximate gauge reading
Status
70°F
35 psi
Correct
50°F
33 psi
Slightly low, top up
30°F
31 psi
Low, noticeable fuel economy cost
10°F
29 psi
Well low, close to the warning threshold
-10°F
27 psi
At or below the 26 psi trigger point
A tire set to 35 psi at 70°F, read at colder temperatures
Set pressures cold, before driving, using the number on the driver's door jamb placard. Tires warm up 4 to 6 psi in the first twenty minutes of highway driving, so filling to placard pressure at a gas station after a long drive leaves you underinflated once they cool.
The placard number, not the sidewall number
This is the single most common inflation mistake. The pressure molded into the tire sidewall — often 44 or 51 psi — is the maximum the tire is rated to hold, not the pressure your car wants. The correct figure comes from the vehicle manufacturer, on a sticker in the driver's door jamb, and it accounts for the car's weight, weight distribution and suspension tuning.
Overinflating to the sidewall number shrinks the contact patch, wears the center of the tread, lengthens wet stopping distances and makes the ride harsh.
Front and rear pressures are often different. Check both lines on the placard rather than assuming one number covers all four.
Loaded vehicles may have a second spec. Many placards list a higher pressure for full occupancy or towing.
Compact spares are different again, commonly 60 psi, and they lose pressure sitting in the trunk for years. Check the spare when you check everything else.
One habit covers almost all of this: gauge all four tires cold once a month, and again at every seasonal change. TPMS is a backstop for a tire that is already badly low, not a substitute for a $10 gauge. Combining that check with your tire rotation schedule keeps both wear and pressure honest.
Frequently asked questions
▸Why is my TPMS light on when all four tires look fine?
Because 25 percent low is not visible. A radial tire at 26 psi instead of 35 looks essentially identical to a full one at a glance — modern sidewalls are stiff enough to hide it. That is precisely the problem the federal requirement was written to solve. Use a gauge, not your eyes.
▸Do I need to reset the light after adding air?
Usually not. Most vehicles extinguish the lamp on their own within a few minutes of driving once every tire is above the threshold. Some require a reset button under the dash or a menu selection. If the light is still on after a 15-minute drive with correct pressures, check the spare and then look for a sensor fault.
▸Can I drive with the TPMS light on?
Drive gently to somewhere with an air pump — that is what the light is for. What you should not do is start a highway trip on it. An underinflated tire runs hot, and heat is what destroys a sidewall at 70 mph. If a tire is visibly flat, do not drive on it at all; driving on a flat destroys the tire and often the wheel.
▸Why does the light flash first and then stay on?
That pattern is the standardized way of reporting a TPMS system malfunction rather than a low tire. Most often it is a sensor with a dead internal battery after 7 to 10 years, a sensor that was damaged or omitted during a tire change, or a set of wheels never relearned to the car. Pressures may be perfectly fine — but the system can no longer tell you if they are not.
▸How much do TPMS sensors cost to replace?
Typically $60 to $250 per wheel installed, depending on whether the shop uses an OE sensor or a programmable universal one, and including mount, balance and relearn. On a vehicle past eight years old, replacing all four at once while the tires are already off usually costs less than doing them one at a time as they die.