Tire Pressure Sensor Fault

01Flashing vs. solid TPMS light — what's the difference?

This isn't guesswork. Federal regulation 49 CFR 571.138 spells out exactly how the malfunction indicator has to behave: it flashes for 60 to 90 seconds when you start the car, then stays lit continuously for the rest of that drive if the problem isn't resolved. A steady light with no flash at startup means a tire is actually low, typically once it's dropped 25 percent or more below the recommended pressure. A light that flashes on startup, or a dashboard message spelling out a sensor or system fault, means the TPMS itself has a problem reading one or more wheels.

That's the whole distinction in one sentence: solid means add air. Flashing, or a fault message, means air won't fix it. Something's wrong with the sensor or how the system is hearing from it.

02What causes a tire pressure sensor fault?

Dead sensor battery. Each TPMS sensor has a battery built into the sealed housing along with the pressure sensor and transmitter. AAA's engineering research on these systems notes that in most cases those internal components aren't individually serviceable. When the battery goes, the whole sensor gets replaced, not just a battery. It's a common reason a fault won't clear no matter how carefully you check your air.

Unpaired sensor after a tire or wheel change. New tires, a wheel swap, or even a rotation can leave a sensor that isn't matched to its current wheel position in the system's memory. Most shops relearn the sensors automatically as part of the job. Some don't, and the fault shows up days or weeks later.

Corrosion or physical damage. Sensors mount at the valve stem, right where road salt, moisture, and curb strikes do the most damage. A cracked or corroded stem can knock a sensor out of communication with the receiver.

Aftermarket wheels or the wrong sensor installed. Cheaper aftermarket sensors that aren't properly programmed for your specific vehicle, or wheels swapped in without sensors at all, will trigger a persistent fault rather than a pressure reading.

03Is it safe to drive with a tire pressure sensor fault?

Short trips at normal speed, yes. The fault itself isn't a mechanical problem with the tire. What you lose is the safety net. With the system down, a slow leak or a genuinely low tire won't trigger a warning until you've noticed a handling change on your own. Get in the habit of checking pressure with a gauge by hand until the fault is fixed.

Worth knowing: TPMS sensors aren't perfectly precise even when they're working. AAA tested eleven 2022–2024 model year vehicles and found displayed pressure readings differed from actual measured pressure by an average of 1.2 to 1.5 percent. In the same test, every tire on each vehicle was deflated to 75 percent of placard pressure, and only five of the eleven lit the TPMS warning at that point. Five more needed the left front pushed another 0.8 to 2.9 psi lower before the light came on. One, a 2022 Ford F-250, never lit it at all, even at 65 percent of placard pressure, though AAA notes that truck's 10,000-lb GVWR puts it right at the upper limit of vehicles required to have TPMS in the first place. A hand gauge is still worth owning even on a car with working sensors.

04How does a shop find which TPMS sensor is at fault?

A tech plugs in a TPMS diagnostic tool that activates each sensor individually and reads back its ID, battery voltage, and whether it's transmitting at all. That takes a few minutes and tells them exactly which wheel is the problem, rather than guessing from the dashboard message alone. It's a quick check — worth asking for before agreeing to replace anything.

Ask to see the readout before you approve work. A sensor that's transmitting fine with healthy battery voltage isn't the cause of the fault, even if it happens to be the newest one on the car. Faults get misdiagnosed most often when a shop replaces whichever sensor is easiest to reach instead of the one the scan actually flags.

05Does a sensor fault need a relearn or a new sensor?

If the sensor itself is fine and the fault traces back to a tire swap or rotation, a relearn procedure re-pairs the existing sensors to the system. Procedures vary a lot by make and model. Some just need a drive cycle, others need a scan tool. That's covered in full in our TPMS reset guide.

If a sensor's battery is dead or the unit's physically damaged, relearning won't help. It needs a new sensor, then a relearn to introduce it to the system. Our TPMS sensor replacement guide covers what that job involves and what to expect to pay.

06When should you get a sensor fault looked at?

Get it checked if the fault sticks around after you've confirmed all four tires are at the correct cold pressure, if it started right after new tires or wheels went on, or if it followed a pothole or curb hit hard enough to notice. A shop with the right tool can tell you in a few minutes whether it's a relearn or a replacement. No need to guess at home.

One more trigger worth mentioning: winter and summer tire swaps. If you run a second set of wheels seasonally, the fault often shows up the first cold morning after the swap, simply because the sensors on the set you just mounted haven't been relearned to that vehicle yet. That's a relearn at a shop with the right tool, not a parts problem.

TPMS warning signal decoder