The TPMS warning light is a yellow horseshoe shape with an exclamation mark in the middle. It's easy to miss, and it only tells you something is wrong, not what.
What the TPMS symbol looks like
It's a flat-bottomed horseshoe with tread marks along the base and an exclamation mark inside. It's the cross-section of a tyre. Drivers often mistake it for a brake or engine light.
A solid light means low pressure in one or more tyres. A light that flashes for a minute or so at start-up, then stays on, usually means a fault in the system itself.
Why the light comes on
- A slow puncture. A nail or screw letting air out over hours or days. The most urgent cause.
- A cold snap. Pressure falls about 1 to 2 psi for every 10 °C drop, so the first cold morning of winter lights up plenty of dashboards.
- Natural air loss. Tyres slowly lose air through the rubber, even with no puncture.
- A tyre change or rotation. Some systems need a reset after wheels are moved.
- A sensor fault. A sensor that has stopped reporting can set the light off too.
Using a screen-and-sensor kit and a tyre has gone quiet? See TPMS not working.
What to do when it comes on
- Ease off. Avoid hard braking and sharp steering until you know what's going on.
- Stop somewhere safe and walk around the car. Look for a soft tyre, a nail head or a bulge.
- Check all four pressures with a gauge. Don't guess which tyre it is. Compare them with the placard, usually on the driver's door jamb.
- Pump the low tyre up to the placard pressure and note which one it was.
- If the same tyre drops again within days, it has a puncture. Get it repaired rather than topping it up.
- If every pressure is right but the light stays on, have the sensors checked.
Why a live reading beats a warning light
Factory systems built to the US rule FMVSS 138 only have to warn once a tyre is 25 per cent below its placard pressure. On a tyre set to 38 psi, that's about 28 psi before the light comes on.
A soft tyre at highway speed builds heat. Many factory systems also show no live numbers, no temperature and nothing for a caravan or trailer behind you.
An aftermarket tyre pressure monitoring system shows live pressure and temperature for every tyre, car and van, and sounds an alarm as a tyre starts to lose air. See every kit and price.
Questions
Can I keep driving with the TPMS light on?
Only a short distance, slowly, to a safe place to stop and check. Driving on for days is how a slow leak turns into a ruined tyre.
Why did the TPMS light turn off by itself?
Almost always temperature. Cold air overnight dropped the pressure below the alert level, and driving warmed the tyre back up. The tyre is still low when cold, so set it with a gauge.
Why is my TPMS light flashing when I start the car?
A light that flashes at start-up and then stays on usually means a fault in the system, not low pressure. Often a sensor has stopped working. A tyre shop can test which one.
Not sure what your rig needs? Email us your rig: info@flatmate-tpms.com
