TPMS and MOT: What You Need to Know

The humble tyre pressure monitoring system, or TPMS, has become a standard feature on many modern vehicles, designed with one crucial goal: to enhance road safety by alerting drivers to underinflated tyres. However, a significant change in MOT testing regulations, implemented since January 1, 2015, means that if your car was registered after January 1, 2012, and is fitted with a TPMS, it must be fully functioning to pass its annual MOT test. Despite these rules being in place for some time, a considerable number of motorists remain unaware of this critical update, potentially leading to unexpected failures during their vehicle's mandatory inspection. This lack of awareness, as highlighted by Stuart Jackson, chairman of the safety organisation TyreSafe, means many drivers are unknowingly risking their MOT certificates and, more importantly, their safety on the road.

The Importance of Correct Tyre Pressure

Underinflated tyres are not just an inconvenience; they pose a serious safety hazard. When a tyre is significantly underinflated, its contact patch with the road surface changes dramatically. Instead of an even distribution of pressure across the entire tread, the shoulders of the tyre are more likely to make contact, while the central section may lift away. This compromised contact patch directly impacts a vehicle's handling and braking capabilities. Reduced grip on the road means a longer stopping distance, less precise steering, and an increased risk of aquaplaning in wet conditions. Ultimately, this can lead to a loss of control, particularly during emergency manoeuvres. The legislation mandating functional TPMS aims to proactively address this issue, reducing the number of vehicles operating with dangerously low tyre pressures.

Understanding the MOT Test and TPMS

The MOT test is a vital annual inspection designed to ensure that vehicles meet minimum safety and environmental standards. With the introduction of new regulations, the functionality of a fitted TPMS has become a direct criterion for passing the test for vehicles registered from January 1, 2012, onwards. If your car falls into this category and its TPMS warning light remains illuminated on the dashboard after starting the engine, or if the system is otherwise not functioning correctly, your vehicle will likely fail its MOT. This means that any issues with the sensors, the control unit, or the warning light itself will need to be rectified before a pass certificate can be issued. It's crucial for owners of vehicles manufactured since 2012 to be aware of this requirement.

Common TPMS Faults and Their Implications

Several issues can cause a TPMS to malfunction, leading to an MOT failure. These can include:

• Faulty Sensors: The individual sensors fitted to each wheel can fail due to battery depletion, physical damage (perhaps from hitting a kerb), or corrosion.
• Damaged Valve Stems: The valve stem, which houses the sensor and allows for tyre inflation, can become damaged or corroded, leading to air leaks and system errors.
• Control Unit Issues: The central control unit that receives data from the sensors can also develop faults.
• Receiver Malfunctions: The receiver that picks up signals from the sensors might not be working correctly.
• Aftermarket Wheels: Sometimes, fitting aftermarket wheels can interfere with the TPMS sensors or their signal transmission.
• Low Tyre Pressure Warning Light: If the warning light stays on after the engine has been started, it indicates a system fault that needs investigation.

When any of these components fail, the TPMS will not be able to accurately monitor tyre pressures, and the warning light will typically illuminate, signalling a problem to the driver and, critically, to the MOT tester.

Manual Checks Remain Essential

While a functioning TPMS is now a legal requirement for MOT tests on relevant vehicles, it is by no means a substitute for regular manual tyre pressure checks. Stuart Jackson of TyreSafe rightly points out that TPMS is a safeguard, a supplementary safety feature, not a replacement for driver responsibility. Drivers still have a duty to ensure their tyres are correctly inflated. This means carrying out manual checks at least once a month and before embarking on any long journeys. Relying solely on the TPMS can be a mistake, as the system primarily alerts you to significant drops in pressure, not necessarily to pressures that might be slightly low but still within a safe range according to the manufacturer's recommendations. Furthermore, TPMS systems can have their own failure modes, as discussed above, meaning they might not always provide accurate information even when the warning light isn't illuminated.

When to Check Your Tyre Pressures

To ensure optimal safety and tyre longevity, and to avoid potential MOT issues, make it a habit to check your tyre pressures:

• Monthly: A regular monthly check is the minimum recommended frequency.
• Before Long Journeys: Before setting off on a significant drive, always check your tyre pressures.
• After Tyre Changes: If you've had new tyres fitted or any tyre work done, check the pressures once the work is completed and again after a short period.
• When the TPMS Light Illuminates: If your TPMS warning light comes on, check your tyre pressures immediately.

Remember to check your tyre pressures when the tyres are cold, as driving heats them up, increasing the pressure and giving an inaccurate reading.

Finding the Correct Tyre Pressures

The correct tyre pressures for your vehicle are not printed on the tyre sidewall itself. Instead, you'll find this vital information:

• On a sticker in the driver's side door jamb.
• Inside the fuel filler flap.
• In your vehicle's owner's manual.

These recommended pressures are crucial for maintaining proper handling, fuel efficiency, and tyre wear. Using incorrect pressures can have detrimental effects on all these aspects.

Table: TPMS Functionality and MOT Pass Criteria

Frequently Asked Questions

Q1: My car was registered in 2013. If my TPMS light is on, will I fail my MOT?
Yes, if your car was registered on or after January 1, 2012, and it is fitted with a TPMS, a continuously illuminated TPMS warning light will cause your vehicle to fail its MOT test.

Q2: I have aftermarket alloy wheels. Could this affect my TPMS?
Yes, aftermarket wheels can sometimes interfere with the operation of TPMS sensors. Ensure that any new wheels are compatible with your vehicle's TPMS, or that the sensors have been correctly transferred and are functioning.

Q3: How often should I check my tyre pressures manually?
It is recommended to check your tyre pressures manually at least once a month and before undertaking any long journeys. Checking when tyres are cold provides the most accurate reading.

Q4: Where can I find the correct tyre pressures for my car?
The correct tyre pressures can usually be found on a sticker located in the driver's side door jamb, inside the fuel filler flap, or within your vehicle's owner's manual.

Q5: Is a TPMS a replacement for manual checks?
No, a TPMS is a safety aid and should not be relied upon as a replacement for regular manual tyre pressure checks. Manual checks are still essential for ensuring optimal safety and tyre life.

Conclusion

The integration of TPMS functionality into MOT testing signifies a commitment to improving road safety. For owners of vehicles registered from January 1, 2012, onwards, understanding and maintaining a functional TPMS is no longer optional; it's a legal requirement that directly impacts their ability to pass their MOT. While the technology offers a valuable layer of safety, it is crucial to remember that it complements, rather than replaces, the fundamental responsibility of drivers to manually check and maintain correct tyre pressures. By staying informed and proactive, motorists can ensure their vehicles remain safe, legal, and ready for the road.