Der Sportwagen

September / October 2014 15 between the wheels. Direct systems are typically found in your Porsche which use a wireless sensor inside the wheel to detect the pressure in the tire. Since this is a Porsche magazine, I will obviously focus on direct systems. This direct sensor is all part of the valve stem assembly as shown above. These direct systems use sealed battery powered units which are quite accurate. Each sensor wirelessly transmits (either on 315 or 433mghz frequency) it's data to the car, which can then be displayed through the dash, and if the tires are low, the small yellow tire light will illuminate on the dash. But what if you air up the tire to the proper spec, and the light does not go out, or maybe the tire wasn't low on air? Well then the battery is probably dead in one of the sensors. Typical lifespan of a TPMS sensor is 5-7 years until the battery finally dies, so we are now starting to see these sensors fail on a regular basis. Unfortunately, since these are sealed units, you can't just replace the battery, but must replace the entire sensor. Remember when you would buy new tires for your car, and the shop would tell you that your $4 valve stems need to be replaced too, and you grumbled because it was an extra 16 bucks? Well, you can think of it like that, but instead of $4, they are $150 each (x4, and that about equals the cost of a set of tires in some cases!), plus whatever bogus fee they charge you to marry the sensors to the car's computer. Upgrading to aftermarket wheels? Well you will either have to swap your sensors from your old wheels to the new wheels (which works just fine in most cases), purchase a new set of sensors for those wheels, or install regular valve stems and just deal with the warning light on the dash all the time….or do you? While the warning light can not just be turned off by the end user, there are ways to deactivate it with a little work. There are still many people who are perfectly happy checking their own tire pressures on a regular basis, so when they upgrade wheels (especially the case for cars used on a racetrack) and use regular valve stems, or have a sensor go bad, they just want to shut the light off. The procedure is not difficult, but does require some reprogramming of the computer. For example, on this 997 Turbo, the owner is running aftermarket wheels with no sensors. The way around this is as follows: In the front trunk, remove the plastic cover which hides the master

• Cover