Achey Breakey Parts: TPMS And Corrosion

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It is not seriously in doubt that TPMS sensors are generally a good safety system. It's known that they have prevented many blowouts and potential injuries caused by loss of pressure. They've also saved millions of gallons of gas from mileage-draining under pressured tires.

But boy do they also cause some major headaches for owners and installers alike. Of the many headaches commonly associated with TPMS monitors, clearly, the achiest and breakiest is the valve stems. First-generation monitors especially, are not only showing the effects of age, but of some rather thoughtless design. Because so many of these sensors are a one-piece design, with the metal valve stem built into the sensor, any damage to the relatively cheap valve stem can make the expensive sensor simply useless.

And these metal valve stems do corrode and break far too easily. Valve stems on TPMS monitors can corrode for a number of different reasons. Knowing these reasons and how to prevent them can mean the difference between happy driving and disaster.

Problem: Metal Valve Caps

While the bright and shiny chrome plated or metal valve caps that you see everywhere are often a nice effect compared to dull black plastic caps, when it comes to TPMS stems, they're a clear and present danger. Metal caps can easily cause corrosion on the threads of TPMS stems as well as beginning to corrode themselves. The result is all too often that the cap will rust-weld itself to the stem, leading to outcomes from the cap simply seizing when a technician tries to remove it, to cross threading issues, or even having the stem break off entirely. When the valve stem is a nonremovable part of the TPMS monitor, this goes from being a minor issue to a critical and often expensive problem.

Solution: Rubber Valve Caps

It's simple: Do not ever put metal valve caps on your TPMS valve stems. Black plastic or rubber caps may be dull and boring, but boring can be good. Having your expensive monitors turned to junk by corrosion is excitement you don't need. As Barry Steinberg from Direct Tire told me, “Initially they were putting out a lot of metal caps on these metal valve stems and they were seizing and cracking and breaking. But ever since they've all gone to rubber valve caps we've seen a lot less of that.”

Problem: Brass Valve Cores

Inside every valve stem is a part called the valve core. It's the part that you press down on to let air out of your tires, and it can also be unscrewed and removed with a special tool to let air out of the tires really fast. Most of the rubber snap-in valve stems out there use valve cores made of brass. Because TPMS metal valve stems are usually aluminum, they cannot use brass cores. The reason is that brass will react to the aluminum and cause the core to weld itself to the stem, making it impossible to remove. The absurdity of the situation is clear – an untrained tire tech, or just one who is not paying attention that day, can cause the destruction of a hundred-dollar TPMS sensor by installing the wrong fifty-cent valve core.

Solution: Nickel-Coated Valve Cores

The only type of valve cores that can be used in TPMS sensors are the specialized nickel-coated cores that are specifically designed to go in the valve stems. It's pretty easy to tell the difference, as the brass valve cores are, well, brass-colored, and nickel cores are silver. It's an easy and important check to remove your valve caps after any work has been done and make sure that yours are silver. If they're not, have them replaced as soon as possible. The nickel-coated cores also need to be replaced with new ones every time they are removed, as the coating is thin and can wear off simply from the action of threading and removing them, which will expose the brass under the coating.

Problem: Air, Water, and Salt

The last reason that TPMS valve stems corrode is simply unavoidable. Stems are exposed to the air, they get wet, and especially in winter conditions, they get exposed to road salt and salt water. Corrosion is just a fact of life when it comes to metal parts, and valve stems are exposed every minute of the day. Collet nuts, the parts that screw down over the valve stem to tighten the whole assembly against the valve stem hole are especially vulnerable to the same kind of corrosion that can cause a valve cap or valve core to seize. Horror stories abound of collet nuts seizing, valve stems breaking at the slightest pressure applied by tire techs trying to remove them, and even of stems breaking off while the vehicle is in motion.

Solution: Proper Maintenance

The only solution to environmental corrosion is constant vigilance, mostly in the form of service packs. Service packs are small packets that tire dealers and installers keep with all the tiny parts and widgets that need to be replaced every time your tires are serviced. These packs will include:

  • A new nickel-coated valve core.
  • A new rubber or plastic valve cap.
  • A new set of rubber gaskets to seal the valve hole in the wheel.
  • A new collet nut.

Service packs, you may note, therefore cover all of the major reasons for corrosion problems I have already noted, that being the major reason they exist. By replacing each of these parts every time your tires are serviced, you keep corrosion at bay, preventing it from gaining a foothold in the cracks and crevices between all these seemingly insignificant little parts. This is why the service packs are so important, why responsible installers will always replace them, and why you should always resist the temptation to save the small fee that they will have to charge you for doing so.

There is also a much more permanent, if somewhat more expensive way of solving TPMS corrosion problems, which is to replace your first-generation TPMS sensors with second-generation aftermarket sensors. Most aftermarket sensors now use a removable snap-in rubber valve stem that not only completely avoids most corrosion problems, but can be easily and cheaply replaced if it is damaged. This is an especially good option to look at if your sensors are more than 6 years old, as the batteries on TPMS sensors are rated to last about 6-7 years, and cannot be replaced. That's another headache entirely.