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TPMS: tire pressure monitoring system

What is TPMS?

TPMS stands for tire Pressure Monitoring System.
It is a built-in electronic system that is used for monitoring the pressure in the tires of your vehicle. It reports real-time information to drivers, alerting them when the tire pressure in one or more tires is inadequate.
The TPMS does this either through dashboard indicators such as a gauge, pictogram-display or a warning light.

Purpose:

Installing a TPMS in your vehicle ensures driving safety and decreases the chances of road accidents. Incorrect pressure in your tires increases the braking distance, and affects the cornering performance of your vehicle.
The TPMS prevents any undue mishaps by detecting under-inflation problems in your tires early, and reduces the rolling (braking) distance. In consequence, the TPMS also reduces the wear on your tire’s tread, preventing them from losing their grip on the road, and improves your vehicle’s handling.
It also increases the efficiency of your vehicle, by reducing the fuel consumption that can result from an incorrect tire pressure. Increased efficiency in turn results in decreased CO2 emissions, and thereby reduces the carbon footprint.

Advantages:

Any faults in the tire pressure are communicated instantly to the driver, pre-empting any problems that can arise.
The TPMS does away with the need for manual tire pressure checks, relying on electronic signals that instantly convey the presence of an improper air pressure level in your tires.

Rules/Legislation for equipping your vehicle with a TPM system:

As of 1st November, 2014, all newly registered motor vehicles and motor homes in the EU must have a TPM system installed.
All types of new vehicles and motor homes must be fitted with a TPM system, as of 1st November, 2012.

What are the requisite capabilities of the TPMS?

As of November 2012, all registered vehicles must be equipped with either a direct or an indirect TPMS system. Vehicles that fail to conform to the mandate are not granted type approval or registration in EU member states. As per the regulations set by the EU, the TPMS must have the following specifications:

  • A pressure loss in an individual tire at 20% lower than the operating pressure (Pwarm) of 1.5 Bar should cause the TPMS to issue a warning within 10 minutes.
  • A sudden or gradual loss of pressure in all four tires at 20% lower than the operating pressure (Pwarm) of 1.5 Bar should cause the TPMS to issue a warning within 10 minutes.
  • It should detect a pressure drop in the tires at speeds between 40km/h and the maximum speed.
  • It should have a data transfer rate at 434 MHz.

What is an indirect TPMS?

An indirect TPMS uses the sensors of the Anti Lock Braking (ABS) system to approximate the tire pressure. The indirect TPMS, or iTPMS, relies on the principle that an improperly inflated tire will have a smaller diameter, and consequently, a higher angular velocity than a properly inflated tire.
As the name implies, the iTPMS cannot measure the direct or absolute pressure value. Their measurements are relative to the speed of each individual tire. Recent iTPMS systems use eigenform and frequency spectrum analysis of the tire’s velocity to ascertain the inflation pressure. Thus, when the tire starts spinning faster than normal, the on-board computer interprets that as an under-inflation signal and alerts the driver.
The iTPMS must be reset after proper inflation and routine tire rotations, and it takes between 20 to 60 minutes of driving for the system to re-learn the new parameters to become completely active.

What is a direct TPMS?

The direct TPMS measures the pressure in the tires through pressure sensors that are installed directly in the tires. These sensors measure the pressure inside the tire and report it to the car’s on-board computer or instrument cluster. Unlike their indirect counterparts, these sensors can also measure the temperatures inside the tire.
These sensors transmit the real-time pressures at each location, both when the car is in motion and when it is parked. Owing to their location in the car’s tires, these sensors are usually powered by batteries and are susceptible to damage. However, some sensors are powered by wireless power systems through electromagnetic induction. This overcomes the short life of the battery-powered sensors. Wirelessly powered systems allow for an increase in the frequency of data transmission and a reduction in the weight of the sensor.
The dTPMS system can be installed both internally and externally. In case of externally mounted systems, the sensors can be either cap-fitted or flow-through sensors. Cap-fitted sensors are large valve caps that screw directly onto the valve-stem, and have to be removed when the tire has to be filled. However, flow-through sensors also thread onto the valve-stems, but allow for air flow through the sensors. Therefore, they don’t need to be removed while filling air into the tires.
Internally mounted sensors are mounted inside the tire with a large metal band that is secured around the tire.

What are the types of sensors used in TPMS systems?

Based on the fittings:

There are primarily three types of TPMS sensors:
Clamp-On Valve TPMS - The valve-stem is an integral part of this sensor and is mounted through the tire’s valve opening. It is secured to the wheel with a separate grommet or ferrule nut.
It should be noted that the grommets are made of a softer metal - usually aluminium - than that of the valve-stems. Once they are sealed, they conform to the shape of the surfaces they are sealed against. Therefore, these grommets should never be reused after changing or servicing the sensors.
The sealing grommets should also never be over-tightened or over-torqued. Doing so can cause the seals to develop hairline cracks, and can even damage the valve-stem and sensor.
Snap-In Valve TPMS - These sensors are almost similar in appearance to non-TPMS valve- stems. These TPMS sensors are usually longer than the valve-stems, and on removing the rubber cap, the sensor has a bevelled brass surface at the base. A self-tapping screw holds the sensor to the valve-stem.
It is important to be mindful of the stress being applied while tightening the sensor to the stem, and also ensure that the valve-stem and the sensor are properly aligned. A failure to do so can cause the stem to snap when it comes in contact with the mounting head.
Band TPMS - In the band TPMS, the sensor is attached to a metal band on the inside of the tire rim, and is affixed opposite to the valve-stem. This type of sensor can still be found in some Ford vehicles.

Original and Programmable Universal Sensors:

Pre-requisites for selecting the sensors for vehicles:

  1. The sensors to be installed must be pre-programmed for the vehicle in which they are going to be installed.
  2. The vehicle and the sensor must be compatible; i.e. not every sensor will fit any vehicle.
  3. In case of summer or winter-tire replacement, the choice must be made between a pre-programmed original sensor and an un-programmed universal sensor.

Original Sensors - These sensors are pre-programmed with the settings specific to the vehicle they are meant for. With the large number of sensors available and the increasingly growing customer base, it would be necessary for workshops to stock all types of sensors, with a minimum of at least four units in stock at any given time, in order to satisfactorily serve customers.
Programmable Universal Sensors - These sensors are not pre-programmed and can be installed on any vehicle. There is no need for workshops to stock a variety of sensors in order to meet customers’ demands. However, programmable sensors need an additional programming tool that is used to calibrate the sensor to the vehicle’s specifications.
This tool first reads the technical specifications of the original sensor and the tire in which it is located, and the collected data can then be used to program the new sensor with the same specifications.
If there is no original sensor available, the tool can generate a new sensor ID before programming the sensor to the required specifications.

How are the sensors installed on the tires?

This installation and dissembling of TPMS sensors in a car requires special tools that are available in the TPMS service kit. These tools ensure the nuts and the valves are installed with the right amount of torque.
The TPMS sensor is usually mounted inside the tire on a certain tire valve. Depending on your requirements, you can choose between a clamp-on aluminium valve and a rubber snap-in valve TPMS.
Snap-in valves are usually cheaper than clamp-on valves, and are easier to install. However, at high speeds, usually exceeding 210 km/hr, snap-in valves can fall short in terms of viability.
During a tire or sensor change, it is advisable to replace all the associated components such as the valve core, valve cap, nut, washers and seals.
Each type of sensor service kit comes with the components as follows:

Snap-In Valve:

  1. Sensor
  2. Rubber Valve
  3. Self-tapping torque screw
  4. Nickel-plated valve insert
  5. Plastic valve cap

Clamp-On Valve:

  1. Valve with moulded sensor housing
  2. Rubber Seal
  3. Gland or Ferrule Nut
  4. Nickel-plated valve insert (core)
  5. Plastic valve cap

Why all the components in the service kit must be replaced:

  • The metal grommets that have been compressed into shape during sealing cannot be reused. They are replaced by rubber grommets from the kit.
  • The original valve-stem nut may have developed hairline cracks or may have been over-torqued.
  • The nickel-plated valve cores provide a better resistance to galvanic corrosion and can retain the integrity of the primary seal.
  • The new plastic caps can prevent dirt and moisture from damaging the sensor, and also act as a secondary air pressure seal.
  • The old washer nut could have developed stress-cracks and will fail to effectively secure the valves to the tires.

Can I use a brass valve core with aluminium TPMS sensors?

No. A brass valve core must never be used with an aluminium TPMS sensor, as it could lead to galvanic corrosion. Galvanic corrosion occurs when two different metals fuse to one another, thereby causing damage to the core and the sensor. A corroded valve-stem will also interfere with the data transmission from the TPMS to the ECU, resulting in a failure of the TPMS warning lamp lighting up.

How does the vehicle re-learn the new sensors?

Once the new TPMS sensors have been installed on your tires, your vehicle must detect the sensors and a communication link must be established between the sensors and the readout device. This would ensure that the central data processing unit of the TPMS is activated whenever a new sensor ID is generated or when the sensor position on the wheel has changed.
Depending on its make, there are three ways in which the vehicle can be made to recognise the new sensors:

  1. Self-Training/Auto-learning - While driving the car for 10 minutes at speeds between 35 to 100 km/hr, the vehicle reads the sensors automatically. The TPMS warning light goes off automatically once all the sensors are read. These are common in makes such as Mercedes, Vauxhall/Opel, VW, Ford, Mazda, and Hyundai.
  2. Manual Teach-In/Stationary Re-learning – This is a fixed procedure using an activation tool, without having to drive the car. The specific procedures can be procured from the makes’ respective manuals such as Audi, Mercedes, BMW, and Porsche.
  3. On-Board Diagnostic Interface (OBD-II)/Programmed Re-learning - The sensors are taught by establishing a connection between them and the on-board diagnostic interface in models such as Renault, Citroen, Peugeot, Nissan, Vauxhall/Opel, Fiat, and Lancia. The OBD-II is also used for diagnostic purposes when the TPMS warning lamp comes on.

What happens if the TPMS re-learn procedure is not carried out completely?

If the TPMS re-learn procedure is not completed, it can result in faulty pressure readings and system failure. Every manufacturer has a fixed TPMS re-learn procedure which should be carried out to the letter to ensure that the TPMS functions correctly. TPMS service workshops should familiarise themselves with the various procedures and should have the necessary service kits on hand to carry out these procedures.

Will the TPMS obligations affect me, and what are the implications of this change?

If you are the owner of a motor vehicle or a motor home, the following applies to you:

  • As of 1st November, 2014, all newly registered motor vehicles and motor homes in the EU must have a TPM system installed.
  • All types of new vehicles and motor homes must be fitted with a TPM system, as of 1st November, 2012.

Many makes have already introduced TPMS systems into their cars prior to the 2012 directive, and can therefore pass the vehicle tests if their TPMS is fully functional.
TPMS tests will be become mandatory in 2015, and vehicles failing to meet the requirements will be rejected during the vehicle tests.
Disabling or bypassing the TPMS system and warning light on your vehicle may become an offence after the directive issued in 2014.

Where can I get the TPMS technology?

The TPMS technology is installed during the manufacture of the vehicle. If your vehicle does not have the TPMS technology, it will not be subject to TPMS obligations. Therefore, there will be no need to retrofit a TPMS system on your vehicle.
A workshop that offers TPMS services can help and advise you on the spare parts needed with your TPMS system, such as valve cores, grommets, replacement sensors, and service kits.
Note: Owing to the complexity of the TPMS system, it is recommended that tire changes and other maintenance work should be carried out by a professional workshop that has the required expertise and tools.

What is the TPMS warning light? What does it mean?

The TPMS warning light looks like this:

The TPMS warning light is flashing on my dashboard. What should I do?

The TPMS comes on when you’re driving: If the TPMS light comes on and stays on when you’re on the road, it means that at least one of your tires is at a low pressure level. Check the pressure in all your tires, to ascertain which one(s) is/are at fault and fill them with air. The TPMS warning light will turn off automatically once the right pressure has been restored to all tires.
The TPMS warning light flashes on and off: This indicates that the pressures in your tires are nearing their lower threshold value (20% of the normal value). This usually occurs when the pressure fluctuates due to changes in the ambient temperature. It is a good practice to periodically check the pressure in your tires, including the spare tires, to ensure that all of them are at the optimum pressure.
The TPMS flashes when you start your car and then stays on: If your TPMS signal flashes for approximately 30 to 90 seconds when you turn on your ignition, and then stays on once your car is running, it means there is a fault in the TPMS itself. Get your car to your TPMS specialist at the earliest to rectify any faults in the system. If the TPMS is faulty, as an additional precaution check the pressure on your tires before driving.

How often should I check my vehicle’s tire pressures?

While punctures and damages can cause your tires to lose air rapidly, tires can still lose air gradually over time due to ambient temperature changes, road conditions and other factors. Therefore, it is recommended that you check your tires atleast once a month. Don’t forget to also check the tire pressure in your spare tires, regardless of whether or not they are equipped with TPMS.

How does tire pressure affect my driving and safety?

Under-inflated tires can affect both wet and dry surface handling while driving in the following ways:

  • Skidding and lack of control while rounding sharp curves or while rounding normal curves at a high speed
  • Hydroplaning on wet surfaces which can affect your stopping distance, and cause skidding and loss of control
  • An increased potential for tire blowouts which can lead to accidents

Under no circumstances is it advisable to drive with under-inflated tires. When your TPMS light warns you about under-inflation in any or all of your tires, take your car to the nearest service centre and rectify the issues.

What should I do if I get a TPMS warning while I’m driving in the middle of traffic?

If the TPMS light starts blinking while you’re driving:
Get a good grip on your steering wheel, in case you need to handle your car in the event of a blowout. Then, slow your car down, and pull your vehicle out of traffic.
Once you are safely out of traffic, measure the pressure in your tires against the recommended value using a tire gauge. A tire gauge is a standard tool that comes in every emergency repair kit.
Fill the tires to the recommended pressure (usually specified in your owner’s manual or in a placard stuck at the bottom of the driver's side door) or if you prefer it, tow your car to the nearest tire service centre and have your tires re-filled and TPMS checked (and fixed).

Is it advisable to use sealants to plug holes for repairs in TPMS-equipped tires?

No. If any substance other than air or nitrogen has been introduced into the tire, it can potentially damage the TPMS sensor. Sealants and breakdown assistants use aerosol sprays that can be detrimental to your sensor. However, if you have used tire sealant in your TPMS tires, have your TPMS service agent assess the condition of your TPMS sensor, and replace it if any damage has been done.

What can cause my TPMS to fail?

The TPMS can fail due to any of the following reasons:
Low Sensor Battery: The internal lithium battery of the sensors has a life expectancy between 4 and 7 years.
Incorrect valve installation: TPMS sensors should be fitted with nickel-plated valve cores, and should never be fitted with brass or copper valve cores. Brass or copper valve cores could lead to galvanic corrosion, which can cause the sensors to fail.
Improper tire changing process and handling: tires fitted with TPMS should be changed using certain procedures based on the type of sensor used. This should be ideally carried out only by TPMS specialists. Rough and improper handling during routine tire changes can cause the sensors to snap or get damaged.
Over-torquing or under-torquing (tightening) of sensors: All the grommets and valves in the TPMS assembly need to be tightened (torqued) to the right amount. If they are not, it can result in a failed TPMS.
Electronic failure: The TPMS uses electronic circuits and devices that can go bad over time.

Will the TPMS warn me if the tires are over-inflated? Are the effects of over-inflating similar to under-inflation?

No. The TPMS is set to go off only when the pressures in the tires drop to 20% of the optimum pressure required.
The effects of over-inflation are as follows:

  • Rough ride while driving over bumps and rough spots on the road.
  • Faster wearing out of the tire treads, especially in the centre.
  • Poor handling due to reduced tire grip.

My car does not have a TPMS. Will I need to retrofit one?

No. Only vehicles that have been fitted with direct or indirect TPMS systems during manufacture fall under TPMS obligations.
However, all vehicles sold from as early as 2004 already come equipped with TPMS systems. If the tires are not fitted with TPMS sensors, the first change will take a longer time and incur an extra charge.

My car has TPMS, but has not yet been serviced by a TPMS workshop. What can I expect?

On your first visit to the TPMS servicing workshop, the following tasks will be undertaken:

  • Verification using diagnostic tools to ensure that your TPMS sensors and system are working properly
  • Servicing or replacement of any defective components in your TPMS system
  • Replacement of TPMS sensor sealing components (cap, core, grommet and nut)
  • Training your TPMS sensors to your vehicle's computer to map the sensor codes to the right tires
  • Final verification of the working of your TPMS system
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