Most cars from the last decade or so have a tire pressure monitoring system. Direct systems have a small sensor inside each wheel, usually built onto the valve stem, that radios the pressure to the car. Indirect systems have no sensors in the wheels. They use the ABS wheel speed sensors to spot a tire that's turning faster than the others because it's low.
The warning light means one of two things. If it comes on and stays on, a tire is low. If it flashes for about a minute at start-up and then stays lit, there's a fault in the system, often a dead sensor or one the car can't read.
Sensor batteries are sealed in and can't be replaced, so a dead battery means a new sensor. Road salt also corrodes the aluminum valve stems many sensors use, and a seized stem can snap during a tire change.
Why it matters
Cold mornings drop pressure
Tire pressure falls roughly 7 kPa (1 psi) for every 5–6 °C drop in temperature. Tires set in September can be noticeably low by January.
Low tires cost you
Underinflated tires wear faster on the edges, use more fuel and run hotter on the highway. The warning catches it before you'd notice by eye.
A light that's always on gets ignored
If the light stays on because of a dead sensor, you'll miss the day a tire actually goes low. It's worth fixing the system rather than living with it.
Signs it's time
- TPMS light stays on after the pressures are set
- Light flashes at start-up, then stays on
- One tire's reading missing from the dash display
- Winter wheels with no sensors fitted
- Corroded or bent valve stems
- Light comes on every cold morning
What's included
- Pressure check and adjustment on all four tires
- Each sensor scanned for ID, pressure and battery status
- Diagnosis of system faults
- Sensor replacement where needed
- Service kit (seal, nut, valve core and cap) at tire changes
- Relearn so the car recognizes each sensor
- Reset of indirect systems after inflation or tire changes
How often
Check pressures monthly
Use the number on the sticker inside the driver's door, not the maximum on the sidewall. Sensor batteries usually last around 5 to 10 years, so older cars tend to need sensors one after another.
