How Do Tyre Pressure Sensors Work? A Simple Guide for Drivers

Author : Jordan Lim | Published On : 15 Oct 2026

A tyre pressure sensor has one job: to tell your car when a tyre has lost too much air. Some sensors do it by measuring the pressure inside the tyre. Others work it out from how fast each wheel is turning. Either way, the result is the same small amber symbol on your dashboard.

This guide explains how tyre pressure sensors work, how the two main systems differ, and what tends to go wrong with them. It also covers why they still do not replace a quick check with a gauge.

What Does a Tyre Pressure Sensor Actually Do?

An under-inflated tyre flexes more than it should. It runs hotter, wears faster along its edges and increases fuel use. In bad cases, it can fail at speed. The trouble is that a tyre can look perfectly normal while sitting well below its recommended pressure.

That is the gap the tyre pressure monitoring system (TPMS) fills. It watches for pressure loss so you do not have to spot it by eye. The wider background on TPMS has its own article on this site, so here we will stay with the mechanics.

How Do Tyre Pressure Sensors Work? The Two Main Systems

A car can monitor its tyres in two ways, and they work quite differently.

Which one your car has is decided by the manufacturer, and your handbook will tell you.

How Direct TPMS Sensors Work

What is inside a direct sensor

A direct sensor is a small, sealed unit. Inside sits a pressure transducer, which turns air pressure into an electrical signal. Many units also carry a temperature sensor, a small processor, a radio transmitter and a battery. The unit is usually mounted on the valve stem or strapped to the inside of the rim, so it sits in the same air as the tyre.

How the signal reaches your dashboard

The sensor sends short radio bursts containing its pressure reading and a unique ID. A receiver in the car picks these up and passes them to the control module. The ID is how the car knows which wheel is which.

The module compares each reading with the pressure the manufacturer set for that model. If a tyre falls below the limit, the warning light comes on. Some cars go further and show the pressure of every tyre on the display. The radio frequency varies by region, which is one reason sensors from another market may not suit your car.

How the battery lasts so long

Constant transmitting would drain a small battery quickly, so sensors save power. Many go to sleep when the car is parked and wake once the wheels start turning. How often they report varies between manufacturers, but the idea is the same: send enough data to be useful, and no more.

How Indirect TPMS Works Without a Sensor in the Tyre

Indirect TPMS has no pressure sensor at all. It borrows the wheel speed sensors that the anti-lock braking system already uses.

The logic is simple. A tyre with less air sits slightly lower and has a marginally smaller rolling diameter, so it has to turn a little faster to cover the same distance. The car’s software compares all four wheels, and when one is consistently out of step, it lights the warning. Some newer systems also analyse the vibration of each wheel for extra detail.

Because nothing is measured directly, the system has limits. If all four tyres lose air at the same rate, the wheels still turn in step, and the system may stay quiet. It usually needs a reset after you adjust pressures or change a tyre, so it can learn the new normal. On the plus side, it costs less, has no batteries and has no sensors to damage during tyre fitting.

Direct vs Indirect TPMS: Which Is More Accurate?

Direct TPMS wins on accuracy. It reports real pressures, spots a single soft tyre quickly and can pick up temperature as well. Indirect systems are less precise, though they are generally reliable at flagging a large drop that could cause real trouble.

Most drivers do not get to choose, since the car arrives with one or the other. Changing from indirect to direct later is possible, but it needs an experienced technician.

When Does the TPMS Warning Light Come On?

The point at which the light comes on depends on the manufacturer and market. Many systems trigger when a tyre falls roughly 20 to 25 per cent below the recommended pressure, and some warn earlier. Your handbook gives the exact trigger for your car.

How the light behaves matters too. A steady light normally means low pressure in at least one tyre. A light that flashes for a short time at start-up and then stays on usually points to a fault in the system itself, such as a failed sensor. In that case, your tyres are not being monitored at all.

Temperature plays a part as well. Pressure rises as tyres warm up on a drive and drops as they cool, so compare readings with the recommended figure when the tyres are cold. Singapore’s steady climate means fewer seasonal swings than in cooler countries, but a long drive in the heat will still push readings up.

How Long Do Tyre Pressure Sensors Last?

Direct sensors run on sealed batteries that cannot be replaced on their own. Life varies with the vehicle, the sensor and how much you drive, but five to ten years is a typical range. When the battery fades, the whole sensor is replaced.

New tyres are the sensible moment to deal with it. With the tyres already off the rim, checking or replacing a sensor adds little labour, and it is also the time to renew the valve seals, nuts and caps. The sensor is also a small weight fixed at one point on the wheel, so the technician needs to allow for it when the wheel is balanced. If you notice a vibration through the steering wheel after a tyre change, have the wheels rechecked at a workshop that offers wheel balancing in Singapore, since an unbalanced wheel wears the tyre unevenly and can shake the whole car. 

Common Problems With Tyre Pressure Sensors

Most TPMS faults come down to a handful of causes:

• A flat sensor battery. Usually after several years of use, it brings on the flashing warning.

• A corroded or damaged valve stem. The sensor sits right where moisture and road grime collect.

• Damage during tyre fitting. This is why an experienced technician matters.

• Sensors not relearned. After a rotation or tyre change, the car may report the wrong wheel or none at all.

• Incompatible aftermarket sensors. The car may not recognise them.

• A second set of wheels with no sensors. If you swap to aftermarket rims, the light will stay on every time they are fitted.

Do TPMS Sensors Replace Manual Pressure Checks?

No. A sensor warns you after a meaningful drop, but the ideal pressure is a precise figure. A tyre sitting a few psi under may never trigger the light and will still wear unevenly and cost you fuel. Anyone who has worked in a tyre bay will tell you the gauge usually notices a problem long before the dashboard does.

Check pressures about once a month, when the tyres are cold, using the figures on the door jamb sticker or in the handbook. Do not forget the spare.

Final Thoughts

Whether your car reads pressure directly or works it out from wheel speed, the sensor is an early warning and not a replacement for a gauge. Find out which system your car has, check pressures monthly and have the sensors looked at whenever new tyres go on.

If the light stays on after you have confirmed the pressures are right, a technician can read each sensor and tell you which one is at fault.

FAQs

Can I drive with the TPMS light on?

Briefly and carefully, to a place where you can check the pressures. A steady light usually means a low tyre, so do not ignore it. If the car pulls to one side, feels unusually soft, or the tyre looks flat, stop safely. A flashing light means the system has a fault and should be looked at soon.

Do tyre pressure sensors need batteries?

Direct sensors do, and the battery is sealed inside the unit. Indirect systems use the car’s existing ABS sensors, so there is nothing extra to run out.

Can I replace a tyre pressure sensor myself?

Valve-cap style external sensors screw on by hand, though they are less common on factory-fitted cars. Internal sensors need the tyre taken off the rim and the sensor programmed to the car, so that is a job for a tyre fitter.

Do TPMS sensors work in cold weather?

Yes, but cold air lowers tyre pressure, so the light may appear on a chilly morning for a genuine reason. In Singapor,e this is rarely a concern, though it is worth knowing if you drive abroad.