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Tire Pressure Light


Tire Pressure Monitoring Systems

What if the vehicle you're driving develops low tire pressure?  Wouldn't you want to be warned?  Low tire pressure can create unsafe conditions in a hurry, particularly in bad weather.

Notice in the graphic below how tire wear may indicate that your tires are either underinflated or over inflated.


Agencies of the Federal government require manufacturers to install tire pressure monitoring systems (TPMS) that warn the driver when a tire is significantly underinflated.  The standard applies to passenger cars, trucks, and other light commercial-type vehicles.

Keeping your tires air the correct pressure for your vehicle is an important factor in how much load its tires can safely carry.  The correct pressure will carry the weight without a problem.  Too little tire pressure will eventually cause catastrophic tire failure.  Studies have shown that people operating their cars with too little air pressure in the tires is common.  It's been estimated that about one out of every four vehicles on the road is running on underinflated tires.  That means that roughly one out of every four drives is negatively impacting their vehicle's fuel economy and handling and costing themselves money by reducing their tires' durability and tread life.

This has made tire pressure maintenance an important safety issue throughout the automotive industry and caused the U.S. government to pass legislation mandating tire pressure monitoring systems.  The main purpose of these systems is to warn the driver if their tires are losing air pressure, leaving the tires underinflated and dangerous.

What types of systems are being used now?  How do they work?  Which works the best?

Vehicle manufacturers have been given options in what systems they can use to comply with the law.

One option is to install a direct tire pressure monitoring system that uses pressure sensors located in each wheel to directly measure the pressure in each tire and warns drivers when the air pressure in any of their tires drops at least 25% below the recommended cold tire inflatino pressure identified on the vehicle place card.

Another option is to install an indirect tire pressure monitoring system that would warn the driver when a single tire has lost at least 25% of its inflation pressure compared to other tires on the vehicle.  It's a little less accurate than the direct system.

Direct Monitoring Systems

Direct tire pressure monitoring systems measure and then warn the driver of low pressure.  Because direct systems have a sensor in each wheel, they generate accurate warning s and can alert the driver instantly if the pressure in any one tire falls below a predetermined level due to rapid air loss caused by a puncture.  In addition, direct tire pressure monitoring systems can detect gradual air loss over time.  Some direct systems use dashboard displays that provide the ability to check current tire pressures from the driver's seat.

Direct systems attach a pressure sensor/transmitter to the vehicle's wheel inside the tire's air chamber.  Most Original Equipment Manufacturers attach the air pressure sensor/transmitter to special tire valves.  The transmitter's signal is broadcast to the in-car receiver and the information is displayed to the driver.  Another way of installing a direct monitoring system is to attach the sensor/transmitter to the wheel with an adjustable metal strap.  These sensors/transmitters and their straps only weigh a few ounces, and can be used on almost all car and light truck wheels.

Important note:  Since standard snap-in rubber valves are still used for the direct method using a strap.  It is important that the owners of these systems let their service department's tire installer know that their vehicle has a direct system banded to the wheel before they change the tires.

Indirect Monitoring Systems

In other original manufacturer's systems, indirect tire pressure monitoring systems were developed by vehicle manufacturers wishing to comply with the law while minimizing the cost.  Indirect systems use the vehicle's anti-lock braking (ABS) system's wheel speed sensors, which are already there, to compare the speed of each tire's rotation to the other ones in a different spot on the vehicle.

If one tire is low on pressure, its circumference changes enough to roll at a little bit higher number of revolutions per mile than the other tree tires.  Reading the same signal used to support ABS systems, the vehicle manufacturers have programmed another function into the vehicle's onboard computer to warn the driver when a single tire is running at a reduced inflation pressure compared to the others.

Indirect systems are less accurate that direct systems because they don't tell the drivers which tire is low and pressure and don't warn the driver if all four tires a losing pressure at around the same rate (like during the fall and winter months when operating temperatures get colder).  Additionally, current experience with the indirect systems indicates that they can generate false warnings sometimes.  The bottom line you sill need to check the tire inflation yourself, or have our service department check it all regular intervals.

The service departments of Russell Barnett Automotive Family located in Winchester, Tennessee, and Tullahoma, Tennessee, are equipped to service any of your tire pressure needs. Call or come by if you have any questions or concerns.