With Tire Pressure Monitoring Systems (TPMS) here to stay, it makes sense to take a look at some of the advantages and disadvantages of today's TPMS hardware. Knowing some of the disadvantages, especially can help both professionals and car owners avoid some pitfalls of this expensive technology.
There is actually only one real advantage to TPMS hardware, but it's a big one – it can save your life and/or your tires. TPMS is designed to warn you by means of a dashboard light when any one of your tires has fallen below 25% of the carmaker's rated pressure. This will let you know you have a problem before the sidewalls of your tire begin to fold over and rub together, which is usually the first tactile warning of a problem. By this time your tires are already damaged beyond repair and unsafe. Running on them for much longer can cause the rest of the air in the tire to exit in a much more uncontrolled manner. Nothing good ever comes of that. By warning you of a problem well before the liner of the tire is worn off, TPMS can not only save your life, it can save you a considerable amount of money.
For the most part, TPMS systems really do tend to work quite well, and it is hard to argue with their intended purpose. There are, however, a number of issues that both drivers and tire techs should be aware of when dealing with TPMS systems.
They're Not Robust:
The vast majority of direct TPMS monitors are part of an assembly that includes the valve stem. When the valve stem is installed the monitor, consisting of an air-pressure gauge and a radio transmitter, sits inside the tire. The major problem with this is that both the monitor and the attached stem are relatively fragile. Because of the way the monitors sit canted against the wheel, dismounting the tire in such a way that the tire bead presses against the monitor can break the monitor or the stem. Because they are known to be so fragile, most tire shops will not accept responsibility for damage to monitors or valve stems. While the sensors on the market are becoming increasingly sturdy and the price of replacing the monitors has been coming down significantly, most OEM sensors are still dealer-only items that can cost $80-$140 apiece. While aftermarket replacements are beginning to enter the market, for now replacing a sensor can be an expensive proposition.
The valve stems themselves are also rather fragile, can snap far too easily, and are liable to corrode much faster than I think they should. There is also a particular problem with valve stems made out of nickel, which most are. The valve core, a tiny piece of metal that screws inside the valve stem, must also be plated with nickel. If a brass valve core, like the ones used in the majority of rubber valve stems, is used in a nickel stem, the two metals will quickly corrode until they are rust-welded together. It is difficult to convey the frustration of seeing a $100 valve stem rendered useless by the wrong five-cent component.
If you have such a system, you therefore want to be particularly careful about who replaces your tires. Do your due diligence and ask questions about whether or not the tire technicians who will be working on your car know how to work with and reset a TPMS system. A good tire shop will not be offended if you ask these types of questions, if only because by now nearly every tire shop has found themselves in the position of explaining to their customer that something someone else did to their car has ruined an expensive monitor.
They're Not Standardized:
Just about every car manufacturer out there now has their own proprietary TPMS systems. There is no standardization, and most of the parts are dealer-only.
They Have To Be Reset:
TPMS computers often have to be reset after a wheel is moved on the car, or if a sensor must be replaced, and the process of finding out how your particular car's system is reset can be maddening. In the best of all cases, your car may simply need to go over 20 miles per hour for 20 minutes or so, easily accomplished by dashing from your wheel repair shop to your next errand. In the worst case your car's manual will require you to push a series of buttons in exact and precise order to reset your system, instructions that sometimes feel more like a game of “Simon Says” conducted in a foreign language. Most shops will have books or software that contain the instructions for reprogramming most systems, but these can be incomplete, confusing, or can directly conflict with the instructions contained in the car's manual.
TPMS is a difficult system in many ways, but even so I must admit that the one big advantage tends to outweigh the several smaller problems. Many of these problems could be fixed - indeed are now being fixed - by improved indirect TPMS systems that use sensors in the ABS hardware to perform their magic. These types of systems are entering the market now, and I suspect that many tire techs would pray for their success.