[Auto] The ABC of the Tire Pressure Control System -TPMS-

[Dr.Drako]

On top of saving fuel, reducing polluting emissions and optimizing tire wear, there is a transcendental point to always have the correct pressure in each of the car's wheels and that is safety. With this point in mind, an active safety technology was developed that was designed to alert the driver to a change in tire pressure.

Called the Tire Pressure Control System (TPMS), this instrument is listed as one of the most essential to safeguard the integrity of motorists and passengers, to the extent that authorities in some countries require them as standard on new vehicles. .

How does the TPMS work?
Depending on the model and / or manufacturer, the Tire Pressure Control System uses the direct or indirect method to detect the air level in the wheels.

Direct: This method uses a battery powered sensor built into the valve assembly to physically measure the absolute pressure of the air within the tire cavity itself. Sensor data on each wheel is transmitted wirelessly to a control module connected to the car's central computer, generating a visible alert to the driver if any tire loses pressure.

Indirect: This method uses existing wheel speed sensors within the Anti-Lock Brake System (ABS) to "measure" tire pressure by detecting differences in wheel rotation speed. A tire with less air pressure will have a smaller circumference and therefore will spin at a higher speed than a wheel that has not lost air pressure.

The data from the wheel speed sensors is communicated directly to the ABS control unit, generating a visible alert if abnormalities in wheel speed are detected.

What to do if the TPMS light comes on?
If the TPMS yellow warning light appears, it means that the air pressure in at least one of your tires has dropped below a minimum tolerance level - around 20-25 percent. This may indicate a leak, a hole, or some other type of damage.

It should also be noted that drastic changes in ambient temperature, such as driving from a cold mountain to a warm valley, can cause direct systems to alert until the temperature stabilizes. Similarly, indirect systems can occasionally confuse uneven tire wear with a fluctuation in tire pressure.

Regardless of the circumstances, if the TPMS warning light comes on, the car must be stopped in a safe area as soon as possible to visually check the tires. If one appears to be deflated but undamaged, try to re-inflate it to the correct pressure and reset the TPMS.

If the wheel has suffered more serious damage, it will be necessary to continue your journey with the spare tire, carry out a temporary repair with a tire repair kit or call an emergency assistance service for a transfer.

How to cancel the TPMS warning light?
Depending on the model, it will be the way to cancel the TPMS alert. While some vehicles equip a physical button under the dash or in the glove compartment, there are others in which it is necessary to enter the computer menu to "reset" this system.

What happens if I replace a tire?
Direct: The condition and function of the TPMS valve and sensor assembly must be verified each time the tires are replaced. This will involve a physical inspection and electronic diagnosis.

The built-in battery has a lifespan of around ten years and cannot be replaced. Electronic diagnostics should reveal the condition of the battery, which will help you decide whether to replace the entire unit at the same time as the tire.

Although the main valve assembly is robust, parts exposed to the atmosphere can deteriorate over time. Therefore, if the battery level is adequate and the main unit is preserved, it would be advisable to replace certain components.

Indirect: Since this system is not directly related to tires, no further action is required, assuming the tires are similarly replaced. However, it is always advisable to replace the valves when changing tires.

Does changing tires affect the TPMS?
Not if the car has indirect TPMS measurement. In which case, you can change tires without the need for additional system programming.

Due to the precision and complexity of direct measurement, the TPMS control module is designed to recognize and communicate with only one set of wheels at a time. Therefore, if a tire is changed, a technician will need to reprogram the control module through the vehicle's OBD port.

There are times when it may be necessary to drive on a wheel that is not equipped with a TPMS valve, such as after a flat tire when the spare wheel is mounted. In such circumstances, the warning light will remain on.

 

Do I have to check the tires manually?
Although the TPMS is designed to issue a safety alert in the event of a significant loss of tire pressure, it is not a substitute for manual inspections. This way you should not skip an inflation check at least once a month.