Understanding Tire Pressure Monitoring Systems

The United States Department of Transportation (DOT) National Highway Traffic Safety Administration (NHTSA) has developed a Federal Motor Vehicle Safety Standard that requires the installation of tire pressure monitoring systems (TPMS) that warn the driver when a tire is significantly under inflated. The standard applies to passenger cars, trucks, multipurpose passenger vehicles and buses with a gross vehicle weight rating of 10,000 pounds or less, except those vehicles with dual wheels on an axle.

Maintaining the correct tire pressure for a 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 can wear out tires prematurely and could create a serious safety concern. Studies have shown that 1 in 4 vehicles have under inflated tires. Under inflated tires will wear out 30% quicker than a properly inflated tire, it will negatively affect the gas mileage performance of the vehicle and the overall handling performance will be compromised.

Tire Pressure Monitoring Systems (TPMS) is designed to warn the vehicle operator if one or more tires on the vehicle were under inflated. The system is designed to send a warning indicator to the driver any time a tire on the vehicle falls 25% below the recommended tire pressure for the vehicle.

There are two approved TPMS systems - DIRECT and INDIRECT

Direct system attaches a pressure sensor or transmitter to the vehicles wheel inside the tire air chamber. The sensor/transmitter sends a signal to a receiver in the car, the receiver then sends a warning to the driver which is displayed on the vehicle dashboard.

An Indirect system uses the vehicle's anti-lock braking systems wheel speed sensors to compare the rotational speed of one tire versus the others. If one tire is low on pressure it will roll at a different number of revolutions per mile than the other three tires. One downfall to this system is if all the tires are under inflated to the same pressure the revolutions will be the same and the system will not warn the driver that all four tires are under inflated.

The most commonly used Tire Pressure Monitoring Systems are the Direct system.

Proper maintenance of the sensors is very important to the overall performance of the TPMS.

Whenever a warning light comes on the dash you should first check the air pressure of all 4 tires (and spare if applicable) to see if any of the tires are under inflated. You can find the proper air pressure inflation information on the inside front door jam of the driver's front door.

Most of the sensor/ transmitter systems are combined with the valve stem. The components of this valve stem are much different from the conventional rubber valve stem. The sensor valve stem has a nickel plated valve core. They use a nickel plated valve core because the core of the sensor valve stem must remain free of any corrosion and nickel will not corrode. The nickel valve core should be replaced anytime the tire is worked on, failure to use a nickel core will result in the core seizing in the sensor, which will result in replacing the entire sensor.

Two other components of the sensor valve is a rubber grommet and a locking ring. These two components should be replaced anytime tires are removed from the wheels and remounted.

TPMS sensors/transmitter have a battery life of about 7 years. The remaining battery life can be checked using a TPMS sensor tool. Town Fair Tire will check the remaining battery life of the sensors on your vehicle at no charge to you.

Town Fair Tire has professionals who are trained in the proper installation and maintenance of TPM systems. If you have checked the air pressure and the warning light is still present stop into any Town Fair Tire for a free analysis of the TPM system.