You're driving along, and a small amber light shaped a bit like a horseshoe with an exclamation mark appears on your dash. It's one of the most misunderstood warnings in a modern car, and plenty of Australian drivers either ignore it or panic about it. Here's what your tyre pressure monitoring system is actually telling you, and what to do next.
What TPMS actually does
A tyre pressure monitoring system watches the air pressure in your tyres and warns you when one drops below a safe threshold. Most systems trigger at around 25% under the recommended pressure, which means by the time the light comes on, the tyre is already meaningfully underinflated.
There are two common types. Direct TPMS uses a small battery-powered sensor inside each wheel that measures pressure and radios it to the car. Indirect TPMS has no sensors at all; it uses the ABS wheel speed sensors to detect that one wheel is rotating slightly faster than the others, which happens when a tyre is low and its rolling circumference shrinks.
The practical difference matters. Direct systems can often show you the actual pressure per corner. Indirect systems only know something is different from the others, so they need to be reset after you adjust pressures or fit new tyres.
Solid light or flashing light?
This is the detail most people miss, and it changes what you should do.
- Solid amber light: at least one tyre is low. Check your pressures at the next servo and inflate to the placard figure.
- Flashing for roughly a minute, then solid: the system itself has a fault. That usually means a flat sensor battery, a damaged sensor, or a sensor that wasn't relearned after a wheel change. Your pressures might be perfectly fine, but the system can no longer warn you, so you're back to checking manually.
Cold mornings set it off
Tyre pressure falls as temperature drops, roughly 1 psi for every 10 degrees Celsius. A Geelong winter morning after a mild afternoon is a classic trigger. The light appears on the first drive of the day and may switch itself off once the tyres warm up.
Don't treat that as a false alarm. It means the tyre was sitting close to the threshold to begin with. Check it cold, before driving, and top it up properly.
What the light can't tell you
TPMS is a safety net, not a substitute for checking your tyres. A few things it won't catch:
- A slow, even loss of pressure across all four tyres, which some indirect systems will miss entirely because nothing looks different between wheels.
- Worn or uneven tread. Pressure and tread depth are separate problems.
- Sidewall damage, bulges, or cuts from a kerb strike.
- Your spare, on most vehicles.
A monthly pressure check with your own gauge, done on cold tyres, still catches more than the dash light ever will.
What to do when it comes on
- Don't slam on the brakes or swerve. Ease off and find somewhere safe to pull over.
- Look at all four tyres. An obviously flat or bulging tyre means stop driving and arrange help.
- If nothing looks dramatic, drive gently to the nearest air pump and check every tyre with a gauge, including the spare if it's a full-size one.
- Inflate to the figure on the placard inside your driver's door jamb or in the owner's manual, not the maximum number printed on the tyre sidewall.
- If the light stays on after correcting the pressures, or comes back within a few days, there's likely a slow leak or a sensor fault worth investigating.
Sensors and new tyres
If you have direct TPMS, the sensors live inside the wheel and have to be handled carefully whenever tyres are removed or fitted. The rubber or metal valve stem seals and service kits are usually replaced at the same time as new tyres. Sensor batteries are sealed in and typically last somewhere between five and ten years, so a light that appears out of nowhere on an older car is often simply a sensor reaching the end of its life.
Ignoring a TPMS warning for weeks is a genuinely expensive habit. An underinflated tyre wears out its shoulders early, uses more fuel, runs hot, and handles worse in the wet, and a tyre that has been run flat often can't be safely repaired afterwards.
If your TPMS light won't go away, or you'd like your pressures, sensors and tread checked properly in one go, the team at Global Tyres Geelong in North Geelong can take a look and sort out whether it's a leak, a sensor, or just a cold morning.