Has a tyre pressure warning light appeared on your dashboard? The yellow symbol looks like the cross-section of a tyre with an exclamation mark inside. But what does the warning light mean, and what should you do about it?
What is the tyre pressure warning light?
The warning light is an alert message to the driver that there may be a loss of air pressure from one or more of the vehicle’s tyres. It comes from the Tyre Pressure Monitoring System (TPMS), an active safety technology that has become a legal requirement for all newly launched and factory updated passenger cars sold in Europe since November 2014.
Tyres represent the only contact your vehicle has with the ground, so maintaining the correct tyre pressure has many safety and efficiency benefits. These include:
- Prevents accidents caused by a critical decrease in tyre pressure
- Helps the vehicle perform predictably
- Saves fuel
- Reduces emissions
- Optimises tyre wear
How does a Tyre Pressure Monitoring System work?
There are two types of TPMS: direct and indirect. Direct systems are installed in the majority of Toyota’s current passenger car line-up, and this method uses a battery-powered sensor integrated into the valve assembly (see images below) to physically measure air pressure from within the tyre cavity itself.
Data from the sensor in each wheel is transmitted wirelessly to a control module connected to the car’s central computer, which prompts a visible alert for the driver if any of the tyres lose pressure. The control module is programmed with the unique serial numbers of the valves within the car’s system. This ensures that the TPMS assembly in each wheel only communicates with its host control module.
The only exception within Toyota’s passenger car line-up is the Proace Verso MPV. This model is equipped with an indirect system, which uses the existing wheel speed sensors within the anti-lock braking system to ‘measure’ tyre pressure by detecting differences in the rate of wheel rotation. A tyre with less air pressure will have a smaller circumference and therefore spin at a faster rate than a wheel that has not lost air pressure.
Data from the wheel speed sensors is communicated directly to the ABS control unit, which prompts a visible alert for the…
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