How Does The Tyre Pressure Sensor Work? TPMS Explained

These systems are charged with monitoring your car's tyre pressure and alerting you when it drops below the recommended level. It may appear to be a small job, but this can dramatically improve your driving performance, the health of your tyres, and your safety behind the wheel.

TPMS can be found in all vehicles that have a manufacturing date of 2014 and later. But what is TPMS exactly? How do the systems work? More importantly, how much does this impact your driving experience? Let's find out:

What Is A TPMS?

Tyre Pressure Monitoring Systems (shortened to TPMS) are fitted to modern vehicles to:

• Monitor tyre pressure
• Report low pressures
• Notify you of tyre pressure imbalances on a vehicle

Within TPMS are a sensor, which activates a dashboard warning light if there is a drop in pressure of between 6-7 PSI. This is now a legal requirement, though some manufacturers set their warning lights to come on when sensors detect much smaller decreases. This provides additional peace of mind.

These devices can be used to determine whether your tyre is frequently leaking air, either through the trim or because of a slow puncture. Solving this problem quickly can reduce the chances of an accident occurring due to a blowout or a flat tyre.

Why Does TPMS Matter?

Roughly 1,200 people are killed on Britain's roads annually because of incorrect tyre pressures. TPMS helps to keep you informed and allow you to respond quickly to deflating tyres or tyres gradually losing pressure. This helps you prevent accidents.

Beyond that, functional TPMS has implications for your MOT test. Having a faulty TPMS can cause instant MOT failure.

Finally, driving with under-inflated tyres could have an impact on their lifespan. They may wear down more quickly and even affect your steering, braking, and fuel usage. To prevent this, you should ensure that your tyres are pressured to the manufacturer's recommendation.

If you've re-inflated your tyre to the correct air pressure and the warning alert is still on your dashboard, you may have a faulty sensor that needs replacing.

How Do Car Tyre Pressure Sensors Work?

There are two main types of TPMS: direct and indirect.

Direct TPMS

These are the most common, as they're more reliable. They use pressure sensors that are located within the tyre to track the pressure. The sensor is fitted inside the tyre to the back of the valve, which is where you apply new air when the tyre needs pumping up.

Because of this location, direct TPMS can track the exact pressure within the tyre, making them accurate and reliable. When the pressure drops past a set parameter – usually 25% – a warning alert will appear on your dashboard. At this point, the car should be taken to a petrol station to have its tyres pumped up. Some TPMS will specify which tyre is low, so you don't have to manually check them all.

These sensors are fitted with an internal battery. However, battery failure is the main reason TPMS stop working. The more miles you go, the quicker the sensor will run down. Unfortunately, for them to work properly, they need to be sealed units – so you can't simply replace the battery when it runs out.

Indirect TPMS

These don't have their own sensor. Instead, they use another sensor that's located inside the wheel, usually the anti-lock braking system's sensor. Indirect TPMS work by tracking the tyres as they revolve.

A tyre that is underinflated will have a smaller radius than a tyre that's properly inflated. Therefore, it will make more or irregular turns. This is how the sensor detects that the pressure could be low. This kind of system is less accurate, but is still able to tell you when a tyre requires more air.

When Was TPMS Invented?

Although it is only now becoming a standard feature in the manufacturing of motor vehicles, TPMS are in no way a new technology. In fact, you'd have to go way back to 1977 to find its origins – but the Porsche 911 was the first commercial car to go on sale with TPMS in 1983.

Renault later adopted the safety system in 1992 for the Renault Laguna and Megane Scenic. Between 2005 and 2007, TPMS were introduced in the U.S. automotive industry as the standard for all new cars.

TPMS became more widely recognised in the U.K. and Europe when EU legislation laws were passed in 2009, stating that from November 2012, all new models of cars must have TPMS as standard.

Where Are Tyre Pressure Sensors?

Direct TPMS sensors are located within the tyre, usually in the space between the tyre and the wheel trim. Indirect TPMS use the sensor on the anti-lock braking system (ABS). The ABS sensor is typically located near the brake rotor. The wheel may need to be removed in order for you to access it.

How To Remove Tyre Pressure Sensor

Occasionally, an indirect TPMS sensor – an ABS sensor – may need cleaning because of where it is located.

• First, check your car's handbook to find exactly where it is situated.
• Next, safely take the tyre off. Ensure that you're using stable jack stands for this job, as you don't want the car to fall off them.
• With the tyre removed, turn the steering wheel, so it's pointing in the opposite direction to the side you're working on. For example, if you're working on the passenger side, turn the steering wheel to the driver's side.
• Place the removed wheel underneath the car (usually under the axle) as a backup – if the jack stands do happen to fail, then at least the car's not going to crash fully onto the ground.
• With the tyre off, you should be able to view the sensor more clearly.
• It'll be bolted in place, so you will need to remove these bolts using a socket wrench.
• Once all bolts are removed, you can remove the sensor easily.
• Using a soap and water solution, carefully clean the sensor with a cloth.
• Bolt it back into place and refit the tyre.

Replacing or removing the direct TPMS sensor isn't as easy, because it's part of the tyre's valve stem. You'd need to actually remove the tyre from the wheel to access it. As professional help is often needed for this job, get in touch with your local Autofusion centre for reliable service and advice you can trust.

Maintain Your TPMS At Autofusion

At Autofusion, we believe in preventative maintenance. We replace the valve every time a tyre is removed from its rim. As the TPMS sensor is just a more complex form of valve, we can service all the various components of the sensor to ensure TPMS valve integrity.

If you have any questions about your TPMS, get in touch with Autofusion today.