Why Your TPMS Light Comes On (and What's Actually Wrong)
We get this call ten times a week starting in October and again in March. A driver wakes up to a 45-degree morning, starts the car, and that little orange exclamation point is staring at them. They pull into a gas station, throw 5 PSI in each tire, the light goes off, and they forget about it for two months. Then it happens again on the next cold snap.
Sometimes that's all it is. Sometimes it isn't. Here's how to tell the difference.
The temperature thing
Tire pressure drops about 1 PSI for every 10°F the temperature drops. If you set your tires to 35 PSI on an 80-degree summer day and don't touch them, by the time you hit a 30-degree January morning you're sitting at 30 PSI. That's below the threshold most TPMS sensors are calibrated to (federal regulations say the light has to come on at 25 percent under spec), and the orange exclamation point appears.
That's why our call volume spikes when the weather changes, not when it gets hot. Hot weather actually makes the light go off, because pressure rises with heat.
If your light comes on after a cold morning and disappears 10 minutes into your drive, that's normal. The friction warms the tires, pressure climbs back, and the sensor stops complaining. Air it up to spec at your next stop and you're done.
Door jamb, not sidewall
This is the single most common mistake we see. The number printed on the side of the tire (something like 51 PSI) is the maximum pressure the tire is rated to handle. It is not what your car is supposed to run at.
Open your driver's side door. There's a sticker on the jamb that lists the manufacturer's recommended pressure for your specific car. For most sedans and SUVs that's 32 to 36 PSI. Some EVs (Model Y, Mustang Mach-E) want 42 PSI front and rear because of the battery weight. Trucks and a few performance cars run higher.
Whatever the sticker says, use that. Don't guess, and don't trust the gas station guy.
When it isn't just temperature
If you've aired up to spec and the light comes back on within a day or two, you have a slow leak. Four common causes:
A nail or screw lodged in the tread. You usually can't see it from a quick walk-around. Spray soapy water on the tire and look for bubbles.
A bent rim. Curb hits and pothole strikes warp the seal between the tire and the wheel.
A rotted valve stem. After 5 to 7 years they crack. The tire holds air for a while between fills, then empties faster each week.
A failed TPMS sensor. The batteries inside the sensors die after about 10 years. If only one tire reads "low" no matter what you do, that's usually the culprit.
A slow leak does not fix itself. The PSI loss compounds, and at highway speed an underinflated tire builds heat fast. The sidewall flexes more than it's designed to, the rubber starts breaking down internally, and that's the failure mode that turns a $40 patch into a $400 tire change on the shoulder of I-40. This is when summer matters: hot pavement plus an already-low tire is the dangerous combination, not the light coming on.
What we do about it
If we get to it before the tire is shot, most slow leaks from a tread puncture are a 20-minute patch on the spot. We carry the plug-and-patch kit in every truck and we don't need you to drive anywhere. If the puncture is in the sidewall or the rim is damaged, we replace the tire wherever you're parked.
If you've been ignoring the light for a few weeks, call before you take a longer trip. We'd rather check it in your driveway on a Tuesday than meet you on the side of US-1 on a Saturday.
What to do today
If your light is on right now and you're not sure why: check pressure on all four tires when they're cold (haven't been driven in 3 hours), compare each reading to the door-jamb sticker, air up anything more than 3 PSI low. If the light comes back on within 48 hours, call us at (919) 526-5165.
We answer 24/7 across Raleigh, Durham, Cary, Wake Forest, and the rest of the Triangle.