Proper tyre inflation is critical for the safety and performance of fleet vehicles, which makes the tyre pressure monitoring system (TPMS) an indispensable feature. But what is TPMS exactly, how does it work, and why does it matter for your fleet?
In this guide we cover how TPMS works, the difference between direct and indirect systems, what the dashboard warning light means, the UK and EU regulations, servicing and costs, and the benefits TPMS brings to fleet compliance and operations.
On this page:
What is TPMS?
TPMS, short for tyre pressure monitoring system, is a vehicle safety feature that continuously tracks the air pressure inside a vehicle's tyres and alerts the driver through a dashboard warning light when pressure drops too low. By flagging under-inflation early, TPMS helps prevent blowouts, which are a common cause of on-road accidents, while also protecting fuel efficiency and tyre life.
In most systems the warning is triggered when a tyre loses roughly 25% of its recommended pressure, which equates to around 6 to 7 PSI on a typical vehicle. On a fleet running many vehicles, that early warning is the difference between a quick top-up and an unplanned roadside breakdown.
How does TPMS work?
At its core, TPMS uses sensors to monitor the pressure in each tyre and transmits that information to the vehicle, presenting a dashboard warning if pressure drops below a safe point. There are two distinct types of system, direct and indirect, and they work quite differently.
How does direct TPMS work?
Direct TPMS works through air pressure sensors mounted on each wheel's valve, which actively monitor the pressure inside the tyre. These sensors typically provide real-time readings for both tyre pressure and temperature, then transmit that data wirelessly to the vehicle, triggering a dashboard alert whenever pressure fluctuates.
Direct TPMS provides more accurate readings and does not need recalibration after tyre inflation or rotation, and its sensor batteries tend to have a longer lifespan, making the system more reliable. The trade-offs are that the sensors are more susceptible to damage during tyre changes, and the system is more costly than an indirect setup.
How does indirect TPMS work?
Indirect TPMS avoids air pressure sensors inside the tyres. Instead, these systems rely on ABS wheel speed sensors to detect pressure loss. By analysing relative wheel speeds, the system infers pressure and compares it across all four tyres: the underlying principle is that an under-inflated tyre has a slightly smaller diameter and therefore rotates faster than expected, which triggers a dashboard alert.
Indirect TPMS is a more economical alternative and demands less frequent calibration, but it needs resetting after tyre maintenance and does not provide precise pressure readings. Slight variations in tyre sizes, for example, can lead to incorrect measurements, and if all four tyres deflate evenly the system may not detect it.
Direct vs indirect TPMS: a comparison
Most vehicles use one of the two system types. This table summarises how they compare.
|
Feature
|
Direct TPMS
|
Indirect TPMS
|
|
How it measures
|
Pressure sensors inside each wheel, usually on the valve stem
|
Infers pressure from ABS wheel speed sensors
|
|
Accuracy
|
High: real-time pressure, often temperature too
|
Lower: estimates based on wheel rotation
|
|
Recalibration
|
Not needed after inflation or rotation
|
Needs resetting after inflation, rotation or replacement
|
|
Maintenance
|
Sensor batteries deplete (typically 5 to 10 years) and can be damaged during tyre changes
|
No in-tyre sensors, so no battery replacement or valve servicing
|
|
Cost
|
Higher hardware and replacement cost
|
Lower, as it reuses existing ABS hardware
|
|
Best for
|
Fleets needing precise, per-tyre and temperature data
|
Cost-sensitive vehicles already fitted with ABS
|
Can you drive with the TPMS light on?
When the tyre pressure warning light activates, it means the air pressure in one or more tyres has dropped below the acceptable threshold. This could be caused by a puncture, damage, a slow leak or other issues, so it should not be ignored.
The warning light itself is usually a yellow symbol shaped like a horseshoe or a cross-section of a tyre, with an exclamation mark in the centre. In some vehicles the letters 'TPMS' illuminate alongside it. In more advanced systems you can also view the real-time pressure of each individual tyre through the dashboard menu.
Sometimes the cause is harmless: sudden changes in temperature, such as moving from a cold environment to a warm one, can trigger alerts in direct systems until the temperature stabilises, and indirect systems can occasionally misread uneven tyre wear as a pressure change. Regardless of the cause, ignoring the light can compromise fleet safety, so it is best to act immediately. Pull over somewhere safe, inspect the tyres, and if any look deflated but undamaged, re-inflate them to the correct pressure.
How to reset a TPMS warning light
If you have checked and correctly inflated the tyres but the light stays on, you may need to reset the system. The exact steps vary by vehicle, so always check the owner's manual, but the general process is:
- Inflate all tyres to the correct pressure. Use the figures on the vehicle's tyre placard, usually inside the driver's door sill, and include the spare if relevant.
- Drive for a short distance. Many systems recalibrate automatically after a few miles at a steady speed, which can clear the light.
- Use the reset function if needed. Some vehicles have a TPMS reset button or a menu option in the dashboard settings; follow the manufacturer's instructions to relearn the baseline pressures.
- Seek servicing if the light persists. A light that will not clear can indicate a failed sensor or a fault that needs diagnostic equipment.
Does TPMS replace manual tyre checks?
No. Although TPMS alerts you to substantial drops in tyre pressure, it is not a substitute for regular manual inspections. Fleet drivers should routinely check each tyre with a reliable pressure gauge to confirm correct inflation, and inspect tread depth to make sure it meets safety standards.
Likewise, manual vehicle checks are still worth doing to catch technological faults and verify accuracy. Even slight deviations from the recommended pressure can cause tyre damage, reduced fuel efficiency, shortened tread life, and poorer braking, cornering, and handling.
Is TPMS a legal requirement?
Yes. TPMS became a legal requirement for new passenger vehicles in the EU from November 2014. The shift began on 1 November 2012, when legislation required all new car models sold in the EU to include TPMS, before expanding in November 2014 to cover all new passenger vehicles sold.
In the UK, further legislation took effect on 1 January 2015: a vehicle with a faulty or inoperative TPMS sensor will fail its MOT test. In practice that means a permanently illuminated or non-working TPMS warning light is an instant MOT failure, so keeping the system healthy is part of staying roadworthy and compliant.
TPMS regulations for trucks and trailers
Initially, TPMS legislation applied only to M1 vehicles, those designed to carry passengers with no more than eight seats in addition to the driver. Recent updates have expanded the mandate to N1 vehicles, which are designed to transport goods and have a maximum mass not exceeding 3.5 tonnes.
TPMS fitment is now also mandatory for further vehicle categories including M2, M3, N2, N3, O3 and O4, covering all relevant trailers within the EU under UN ECE R-141, a key provision of the EU's Vehicle General Safety Regulation. The aim is to increase road safety while cutting unnecessary fuel wastage. For fleet operators this is where TPMS moves from a car feature to an operational requirement across HGV tyres and trailers, and it aligns closely with the transport sector's sustainability objectives.
Can you fit TPMS to an older vehicle?
Yes. Vehicles built before TPMS became mandatory can be fitted with an aftermarket system. These kits use external sensors that screw onto the tyre valves, or internal sensors fitted inside the wheel, paired with a small display or a smartphone app that shows live pressures and warns of any drop.
For fleets, retrofitting brings older vehicles up to the same safety and monitoring standard as newer ones, which supports consistent predictive maintenance across a mixed-age fleet rather than leaving gaps where the oldest vehicles are the least monitored.
TPMS servicing, maintenance, and costs
Over time, the internal battery of a direct TPMS sensor depletes and the sensor needs replacing. Sensors can also fail due to weather exposure, corrosion or accidental damage. To keep the system working correctly and avoid an MOT failure, routine servicing matters, and this often involves specialist diagnostic equipment to inspect and maintain the system. Many manufacturers recommend replacing the valve cap and core components every time a tyre is changed.
Direct TPMS sensor batteries typically last 5 to 10 years and are sealed, so when the battery weakens the whole sensor is replaced. As a rough UK guide, direct sensor replacement is often in the region of £60 to £150 per sensor including fitting, though this varies by vehicle and sensor type. Indirect systems, which estimate pressure from wheel rotation, do not need battery replacement or valve servicing, but they do need recalibration when tyres are inflated, rotated or replaced.
Regular servicing extends sensor lifespan, prevents corrosion in the valve, and maintains an airtight seal, all of which reduces vehicle downtime and keeps the fleet compliant.
Why is TPMS important for fleets?
TPMS is important because under-inflated tyres on commercial vehicles are a common precursor to serious accidents, and its core purpose is to prevent them through proper tyre maintenance. Beyond safety, TPMS adds value across fleet management by delivering:
- Enhanced safety: optimal tyre pressure supports the safety and manoeuvrability of trucks and trailers, improving road safety for drivers and other road users.
- Cost reduction: keeping tyres in optimal condition minimises unplanned downtime and delivers tangible cost savings.
- Lower fuel consumption: properly inflated tyres improve fuel efficiency, reducing both expense and CO2 emissions.
- Extended tyre lifespan: maintaining correct pressures prolongs tyre life, lowering replacement frequency and cost.
For practical ways to turn these benefits into savings, see our 8 tips to improve safety and reduce costs with TPMS.
TPMS with MICHELIN Connected Fleet
In short, TPMS not only guards against accidents but also delivers real benefits in safety, cost-efficiency, and environmental sustainability across fleet operations. So while new regulations can initially prompt a negative reaction, failing to comply with TPMS requirements actually puts your fleet at a serious disadvantage.
Recognising the pivotal role of TPMS, we at MICHELIN Connected Fleet have developed our own tyre pressure and temperature monitoring solutions, which empower fleet managers with real-time alerts for dangerously low tyre pressures alongside set temperature thresholds that flag when a service intervention is needed.
If you want to mitigate major breakdowns, reduce costly repairs, minimise unscheduled downtime, curtail excessive fuel consumption and uphold regulatory compliance, then be sure to make an enquiry into our services today.
TPMS FAQs
How does a TPMS work?
A TPMS uses sensors to monitor the air pressure in each tyre and sends that data to the vehicle, which shows a dashboard warning if pressure drops below a safe level, typically around 25% below the recommended figure. Direct systems use pressure sensors inside each wheel, while indirect systems infer pressure from ABS wheel speed sensors.
How do you reset a TPMS?
First inflate all tyres to the correct pressure, then either drive a short distance to let the system recalibrate automatically or use the vehicle's TPMS reset button or dashboard menu, following the owner's manual. If the light will not clear after that, a sensor may have failed and need replacing.
How long do TPMS sensors last?
Direct TPMS sensors are powered by a sealed internal battery that typically lasts 5 to 10 years. Because the battery cannot be replaced on its own, the whole sensor is renewed when it weakens. Indirect systems have no in-tyre sensors, so they have no battery to replace.
.svg)
.png?width=600&height=400&name=MCF%20Content%20Image%20(9).png)
-1-1.png?width=461&height=443&name=ses_pictograms_ecosystem%20partners_black%20(002)-1-1.png)
.jpeg?width=301&height=341&name=Untitled%20design%20(95).jpeg)
