Tyre pressure monitoring is a great system to have, it allows you to be confident your tyres are at the correct pressure without needing to manually check each one. However, you may sometimes find the system mistakenly warning you of low tyre pressure, especially in the cold!  

This blog post will explain why this is, other causes of your tyre pressure light illuminating and what you can do to mitigate this.  

What is a Tyre Pressure Monitoring System and how does it work? 

As the name suggests, most tyre pressure monitoring systems or TPMS reads the air pressure in your tyres constantly and communicates this to a module in the car wirelessly.  

When the sensors detect a pressure that is lower than it should be, an alert will be shown to the driver in the form of a small light, a message on the dash screen, an audible tone or a combination of the three.  

There are two different types of TPMS, which work in different ways: 

Direct TPMS 

Direct TPMS works as described above, using a small electronic pressure sensor mounted inside the tyre, attached to the wheel, it reads the internal tyre air pressure and sends this to a control module inside the car.  

Indirect TPMS 

A less sophisticated but easily implemented version of TPMS is the indirect variety, this does not use any extra sensors inside the wheel or module inside the car. Indirect TPMS uses the car's existing wheel speed sensors - also used by the ABS and stability control systems - to measure the number of rotations each wheel does.  

If one wheel is rotating slightly faster than the others, the system knows that the tyre is low on air pressure, this is down to the fact that lower air pressure effectively decreases the diameter of the wheel, causing it to rotate faster at any given speed. 

How does cold weather cause a low tyre pressure light? 

Due to the high thermal expansion of air, cold temperatures cause a drop in volume and therefore pressure in your tyres; up to 2 PSI per 10°C. If you put 35 PSI in your tyres on a 25°C day, it will drop to 30 PSI at 0°C. This could be enough to trigger a low-pressure warning in your TPMS system. 

If your TPMS alert comes on, even in cold weather, the first thing to check is your tyre pressure. This can be done quite simply with a pressure tester, available from many motoring stores in the UK such as this one in Halfords.  

If your tyre pressures are low, you should inflate them as per your car's manual, many cars also list the recommended pressures on a sticker in the driver's side door frame too. 

What to do when the tyre pressure light comes on 

If your tyre pressure light comes on, you should check your tyre pressure as soon as possible.  

If the tyre pressures are low, inflate to the correct PSI, accounting for how many people and luggage you will be carrying, as stated in the car's manual. We’d recommend purchasing an old style foot pump and using that to add some air pressure, that way you won't need to seek out and drive to the nearest petrol station.  

If your tyre light is still lit, there is likely to be a problem with the system. One common cause is the batteries in the sensors depleting. Many tyre shops can replace these for a small fee when changing tyres.  

Can I ignore the low tyre pressure light if it's cold? 

No, we don't recommend ever ignoring a warning light on the dash, it’s always best to at least do a quick visual inspection of your tyres if the light is illuminated. 

To help with the issue, re-check your tyre pressures and re-inflate if needed when a cold spell arrives. If the light continues to come on, it may be time to take the car to a garage to check your pressure monitoring system. 

Other causes for a tyre pressure light on the dashboard 

Punctures 

Unfortunately, punctures are something we’re all likely to experience as car drivers, screws, nails, pieces of glass and more can often be found on the road. If a screw or nail is still inside the tyre, it may cause a slow puncture, and remain undetected until your tyre pressure light warns you.  

If your tyre is deflating slowly, say over a few days, you should be able to drive a short distance after re-inflating it. But be sure not to leave it too long or drive too far.  

Time between inflating 

Tyres and valves can’t seal perfectly, expect to need to re-inflate your tyres every 5-6 months due to normal air leakage, but check them at least once a month. Low tyre pressures can affect how your car handles and brakes, as well as causing reduced fuel economy. 

A faulty or incorrect tyre pressure monitoring system 

As TPM systems age, the sensors deteriorate and their batteries deplete. This will generally cause the tyre pressure light to illuminate, alerting the driver of a fault with the system.  

Another cause can be if the TPMS parameters are incorrectly set, as the correct tyre pressure varies from model to model and depending on the amount of luggage or people are being carried, the TPMS can be adjusted to accommodate.  

Speak to an expert 

If your tyre pressure warning light is illuminated and you don’t know what to do let Bumper take care of it for you. 

Split the cost of repairs up to £5,000 and choose from 1,000s of trusted repairers nationwide.