The purpose of the tyre pressure monitoring system is simple, notify when a tyre has low pressure. TPMS have become common place since mandated by the United States in 2007. Two different methods of tyre pressure monitoring are in use, Direct and indirect. Lets have a look at the system operation.
Direct TPMS: This system uses pressure sensors inside each tyre to monitor the air pressure. These sensors transmit data wirelessly to a central control unit, which then displays the information on the vehicle's dashboard. If the pressure drops below a certain threshold, a warning light or message will notify the driver.
Indirect TPMS: Indirect TPMS relies on the vehicle's anti-lock braking system (ABS) and other sensors to monitor the rotational speed of each wheel. When a tire's pressure is low, its circumference changes, leading to a difference in wheel speed. The system detects this difference and alerts the driver.
The claimed benefits of TPMS
1. Safety: Maintaining proper tyre pressure is crucial for vehicle safety. Underinflated tyres can lead to reduced traction, longer braking distances, and an increased risk of accidents. TPMS helps prevent these dangers by alerting drivers to low tyre pressure promptly.
2. Fuel Efficiency: Properly inflated tyres contribute to better fuel efficiency. TPMS encourages drivers to maintain the right tyre pressure, which can save money on fuel costs and reduce environmental impact.
3. Extended Tyre Life: Maintaining the recommended tyre pressure can extend the lifespan of your tyres, reducing the frequency of replacements and saving you money.
4. Convenience: TPMS eliminates the need for manual tyre pressure checks, making it easier for drivers to ensure their tyres are properly inflated (direct system only).
Legalities: In many regions, TPMS is a legal requirement for all new vehicles, as of reports in January 2022 TPMS is not a legal requirement in Australia. Australia being very small portion of the global car park, somewhere around 1.5%, car manufacturers are not influenced by us. In a nutshell we will get what the of the world gets.
Some say the TPMS sensors used on the direct system require regulator inspection. I must disagree. The tyre must be removed to inspect the sensor as a large percentage of the sensor is positioned on the inside of the rim. If a sensor failed, the TPMS lamp will turn on. Sure, you can inspect the stem of the sensor for physical damage but that is all. These same sensors have an internal battery with a life of up to 10 years. Has anyone ever believed statements containing the works UP TO. Replacement sensors are an additional cost for the owner.
Both indirect and direct systems do require system resets either manual (scan tool / button press) or automatic diving vehicle at a given speed or for a given time.
A few glitches we have experienced with TPMS.
Direct system reporting tyre pressures at correct pressure as per tyre placard but the TPMS lamp is on and will not go off. This is a common occurrence on Hyundai vehicles without a TPMS reset button. In this instance to get the TPMS warning lamp to turn off we have used the following procedure:
1. Set the cold tyre pressure to 40PSI. Cold tyre pressure itself can be tricky. Generally, it means the tyres are at ambient temperaurte. An infrared thermometer / type temperate gauge (everyone has those, don’t they) can be used or the tyres can be treated as cold when the vehicle has not been driven for 8 hours.
2. Drive vehicle a short distance until lamp goes off. Often less than half a kilometre.
3. Set correct cold tyre pressure +1PSI. Some vehicles with the direct system that displays the tyre pressure reading on the dash will not give a pressure reading until the vehicle has been driven this short of distance. Set the tyre pressure by the dash display reading.
4. The next time the vehicle is driven with cold tyres check the tyre pressure reading on the display is at the required pressure.
We have seen indirect TPMS where the TPMS lamp will not turn off with a single press of the TPMS button. In this instance multiply button presses and cycling of the ignition switch allowed the lamp to turn off.
As all these systems are added to vehicles, we are seeing more and more idiosyncrasies where multiple reset are required to turn off warning lamps only on some occasions for the warning to return a day later to be reset again before the warning lamp will remain off.