In April 8, 2005, the National Highway Transportation Safety Administration issued its final rule on Tire Pressure Monitoring Systems. It became the outgrowth of Congressional action following widespread rollover accidents with SUVs attributable to under-inflated tires. NHTSA concluded that if motorists were alerted about low tire pressure through TPMS technology, as many as 79 deaths and 10,365 injuries could be prevented each year on American roads. The regulations relating to all of this are full of countless details and bureaucratic jargon, so we'll spare you that.
But here is the straight scoop on what TPMS technology means to you today in the service bay.
WHERE DOES TPMS APPLY?
By law, manufacturers of vehicles sold in the U.S. below 10,000 lbs. gross vehicle weight are required to have TPMS technology onboard. Its mandated application, however, didn't come in one broad brush. Rather, beginning with 2006 models, 20 percent of a manufacturer's models were required to have TPMS. That escalated to 70 percent for 2007 models, and across the board for 2008 models. (It's important to note that some vehicles prior to 2006 had TPMS as an option.)
As you can see, this quick ramp-up makes it likely that TPMS is already rolling into your shop, and the technology will be on everything you service in the not-too-distant future.
TYPES OF SYSTEMS
Although TPMS on any given vehicle may be made by a number of different companies, the technology itself falls into two different types, indirect and direct. It's important to note the difference:
• Indirect TPMS technology "piggybacks" on a vehicle's ABS, using it to calculate different wheel speeds as detected by the wheel-speed sensors. Theoretically, as tire pressure drops, so does the diameter of the tire, resulting in increased rotation speed. By comparing wheel speeds against one another with the right logic, a determination can be made about low tire pressure. The Achilles' heel to the indirect TPMS is that it can't detect which tire is low, or if all tires are low at the same time. Indirect systems were mainly used on vehicles predating the NHTSA final rule in 2005.
• Direct TPMS employs pressure sensors/transmitters located inside each tire to continuously track air pressure and temperature. Those values are transmitted via radio frequency to a computer for analysis and display on the vehicles' instrument panel. The sensors/transmitters may be mounted to the tire valve stem itself, the rim or the tire. Only direct systems really meet the spirit of the final rule and are therefore the best technology. As a result, direct TPMS can detect which exact tire is low and even if all four happen to be low at the same time.
By law, TPMS has to perform some key tasks in order to deliver
on the safety improvement goals that NHTSA rolled into its final rule. They include:
• Pressure sensors/transmitters in all four tires (Spare tire monitoring is not required by law).
• TPMS must be operational whenever the ignition is on and alert the motorist via warning light when any one of the four tires falls 25 percent or more below the placard-specified inflation pressure.
• The warning light must stay lit until either proper inflation pressure is restored or the system fault triggering the warning light has been remedied.
• The TPMS must have a warning light test, activated when the ignition is turned to the "on" position.
• The vehicle owner's manual must have appropriate information including warnings about the TPMS, specifically mentioning incompatible replacement tires.
How do you know if the vehicle you're servicing has TPMS?
Obviously, from 2008 forward, it's a no-brainer since all cars have it starting with
that model year. For 2007 and prior models, look for two tell-tale signs.
Since they come standard with all light-duty vehicles anyway, your fleet might as well start reaping the benefits.
Insight on servicing TPMS.
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