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I have assumed that the tire pressure sensors on my '98 had batteries in them but was told on more that once that there was no battery and the power was generated by some type of counterbalance similar to a self winding watch. That made some sense since the pressure was not displayed until 10-15 mph.
The mystery has now been solved because yesterday I dissected a bad sensor and the do have batteries. All of the components are sealed in epoxy so the units are not repairable nor can the batteries be replaced. Just thought I would pass the info along.
Sorry but at the time I wasn't thinking about pictures. Since everything is imbedded in epoxy you have to break it apart as you chip pieces out so there wasn't much left of it anyway. I can tell you that the battery is on one end and is about the size of a quarter.
Steve
I occasionally drive my car to the track with my autocross tires on it, these wheels do not have sensors in them. The tire pressure that is displayed in the DIC actually changes to reflect ambient conditions. Apparently the sensors transmit 'absolute' pressure (relative to a vacumn rather than atmospheric). The computer then adjusts this based on the ambient conditions. Its pretty weird to see the tire pressures go up as the temperature rises when there are no sensors present.
From: Well Mr. Peabody, where are we going today? Virginia
Re: Tire Pressure Sensor Update (CarolinaC5)
When I park it at night, the pressure is 35. When I turn it on the next morning (before leaving the garage) the pressure is 31. It doesn't have to be driven to register the pressure.
That's the last pressure it took when you were driving the car
According to my Service Manual, the 2001 sensors (don't know about other years) go into a sleep mode if the car has not moved for a while, and only transmitt a pressure reading once per hour. But that would be enough to give you the correct pressure as the tires cool overnight. I've also noticed that if I put air in the tires and then drive right away, it can take a mile or two for the additional pressure to show up on the DIC, but I don't know why. Also, last winter I put on the Winter EMTs and forgot to retrain the sensors- I drove about 70 miles before the DIC finally told me to service the system. Strange.