Q. What is the deal with this low tire pressure light that keeps coming on in my car? It is so annoying and I can't seem to get it to stay off. The tire pressure seems fine. Help!
A. Tire pressure monitoring systems (TPMS) have been around since the mid 1980s in Europe but were not mandated here until the mid-2000s.
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In the late '90s we had the big Firestone tire recall as a result of all of the rollover accidents in the U.S. subsequently linked to tread separation. The result of these accidents forced President Clinton's administration to enact the "TREAD Act." This legislation mandated that by September 2007 all vehicles sold in the U.S. would have TPMS capabilities. The phase in for these new systems began in 2005.
Initially there were two different types of systems that achieved the desired results of monitoring tire pressure: Indirect TPMS and Direct TPMS.
The indirect monitoring system typically utilized the wheel speed sensors from the anti-lock brake system (ABS) to calculate if one or more of the tires was low on air by doing a calculation based on the rotation of the tire compared to the other ones. This system worked but it did not report air pressure and it did not necessarily tell you which tire was low. The benefit to these systems was there were no additional parts needed, other than some programming, and they were very customer friendly.
With direct monitoring you actually have a small radio transmitter in each wheel that reports the actual air pressure to the control module, which in turn alerts the driver to the problem. It will tell you which tire is low and the air pressure. The benefits to these systems are obvious but the downside may just be starting to show.
These small radios have batteries in them and those batteries have a limited life. In addition, the valve is part of the sensor and they can be damaged by hitting a curb, or salt can get in and corrode the valve so badly it cannot be removed. They can also be damaged while changing a tire.
This system is not as customer friendly in that you need a fairly expensive tool to reprogram the sensor after replacement or even after rotating the tires. The computer needs to know which corner of the car each sensor is on, so if you rotate the tires you have to inform the computer where you put it.
If the air pressure on your tires is correct, and you have one of the early direct systems, you may be dealing with a sensor that is starting to fail. If programming does not help, you may want to consider replacing all the sensors as they all may start to fail one at a time.
I sense this is going to be a bit of a frustrating time for the motoring public as they begin to realize this new expense that is now on the horizon.
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