Engineering Definitions of Terms
"A" "B" "C", "D", "E", "F", "G", "H", "I", "J", "K", "L", "M",
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Tire Pressure Monitoring System

TPMS; Tire pressure monitoring systems continuously monitor the pressure in the tires through sensors located in the tires (direct system) or the use of wheel speed and other vehicle sensors (indirect system). The information collected by the sensors is transmitted to an on-board processor that interprets the sensor signals and warns the driver when tire pressure is below the minimum acceptable level by illuminating a warning lamp. The TPMS would not be required to monitor the spare tire (if provided) either when it is stowed or when it is installed on the vehicle.

The U.S. government, through the National Highway Traffic Safety Administration [NHTSA], Department of Transportation [DOT], requires that all passenger cars, light trucks and vans (Gross weight less than 10,000 pounds) be equipped with a TPMS starting in model year 2008. Due to a phase-in of the requirements, 20 percent of model year 2006 and 70 percent of model year 2007 vehicles are equipped with TPMS. The requirement is technology-neutral so the requirements only need to be meet.

Companies making Pressure Sensors

GAWR: Gross Axle Weight Rating

FMVSS: Federal Motor Vehicle Safety Standard. A standard developed by the National Highway Traffic Safety Administration. This particular [TPMS] final rule is effective April 8, 2005. FMVSS No. 138 is a performance standard. FMVSS No. 138 requires new passenger cars, multi-purpose passenger vehicles, trucks, and buses with a gross vehicle weight rating (GVWR) of 4,536 kg (10,000 pounds) or less, except those with dual wheels on an axle, to be equipped with a TPMS to alert the driver when one or more of the vehicle's tires, up to a total of all four tires, is significantly under-inflated. Specifically, the TPMS must warn the driver when the pressure in one or more of the vehicle's tires is 25 percent or more below the vehicle manufacturer's recommended cold inflation pressure, or a minimum level of pressure specified in the standard, whichever pressure is higher.

TREAD: Transportation Recall Enhancement, Accountability, and Documentation. The act that generated the need for the Tire pressure monitoring system. The TREAD Act was enacted by Congress on Nov 1, 2000.

TPMS is capable of detecting when one or more [up to four] of a vehicle's tires is significantly under-inflated, 25 percent or more below the manufacturer's recommended inflation. If any tire drops below the standard's activation threshold, the TPMS is required to provide the low tire pressure warning by illuminating a yellow telltale within 20 minutes of additional travel within a speed range of 50-100 km/hr. This telltale flashes for one minute when a malfunction is detected, after which the telltale must remain illuminated as long as any of the vehicle's tires remains under-inflated and the vehicle's ignition locking system is in the On (Run) position (and re-illuminate upon subsequent vehicle start-ups) until the under-inflation condition has been corrected.

Compliance Date: Consistent with the phase-in commencing October 5, 2005, all new light vehicles must be equipped with a TPMS that meets the requirements of the standard by September 1, 2007, with the following exceptions. Vehicle manufacturers need not meet the standard's requirements for the TPMS malfunction indicator and related owner's manual language until September 1, 2007 (i.e., at the end of the phase-in), and vehicles produced by final-stage manufacturers and alterers must be equipped with a compliant TPMS (including a malfunction indicator) by September 1, 2008. However, manufacturers may voluntarily certify vehicles to FMVSS No. 138 and earn carry-forward credits for compliant vehicles, produced in excess of the phase-in requirements, that are manufactured between April 8, 2005, and the conclusion of the phase-in.

Under-inflation of tires increases the likelihood of many different types of crashes, including those involving: skidding and/or loss of control of the vehicle; hydroplaning; an increases in stopping distance; flat tires and blowouts, and overloading of the vehicle.

Components such as the electronic control unit (ECU) or vehicle speed sensors are involved in TPMS operation.

----: A vehicle inspection and maintenance program.

Diagnostic Trouble Codes: [DTC] An alphanumeric code which is set in a vehicle's onboard computer when a monitor detects a condition likely to lead to (or has already produced) a component or system failure, or otherwise contribute to exceeding emissions standards by 1.5 times the certification standard.

Gross Vehicle Weight Rating: [GVWR]

Malfunction Indicator Light: [MIL] The Malfunction Indicator Light of MIL is illuminated on the dashboard when conditions exist likely to result in low tire pressure. Note that the MIL is also known as the Check Engine light for OBDII [Auto Emission].

Readiness Code: A status flag stored by a vehicle's onboard computer which is different from a DTC in that it does not indicate a vehicle fault, but rather whether or not a given monitor has been run (i.e., whether or not the component or system in question has been checked to determine if it is functioning properly).

Scanner or Scan Tool: A PC-based or handheld device used to interface with a vehicle's onboard computer for the purpose of reading DTCs and monitor readiness status.

Test-and-Repair: An I/M program which allows the same people who test a vehicle to also repair the same vehicle and retest it to determine whether or not the repairs performed were adequate. Test-and-repair programs are also generally decentralized, though not all decentralized programs are necessarily test-and-repair.

PC motherboard

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