where is the battery, in the tire, if so that's real stupid.

 

yup, part of the sensor.

 

8-10 years i think i read somewhere..give or take

EXCELLENT topic, this thread will be active for sure come that day.

Can't just replace battery.

You are looking at buying new sensors……great design eh.

 

The ones in my 07 Sprinter (bought in 06) are still working. Battery life is reported to the WCM (wireless gateway) and all show as having moderate power.

where is the battery, in the tire(?) if so that's real stupid.

Where else would you put the battery? It's either battery in the tire/rim or a very expensive and problematic slip ring made into the hub, and a connector to undo every time you pull the wheel.

Suppose you could do something like put a kinetic generator in each wheel (sort of like what they use in wristwatches) but that would make them a lot more expensive, and they would be difficult to ruggedize.

It's relatively cheap to break down a tire. Lithium cells last a LONG time, and these don't use much power. I think they made the right choice.

 

Last night driving in sub freezing temperatures the TPM indicator light started flashing on and off. Never staying on more than a second or two. Is this an indication of the TPMs starting to fail? Or could it be due to the extreme cold temperature?

 

Very cold temps will cause lower pressure in the tire(s), which will trigger the light. It would be worth checking pressures at your convenience.

 

I found this, looks like about 7 years 100,000 miles. I hope mine fail a bit sooner and Subaru covers them under the extended warranty.

Subaru TPMS and how it works | MNSubaru

exert below;

In a direct read system(like Subaru's chosen one), There is a sensor mounted directly in the rim. Some are mounted on a band that goes around the center of the rim. Others, as is Subaru's (Schrader TPMS) are mounted on the valve stem via a small torx head screw inside the rim. The direct read sensors read the actual air pressure in the tire VS. counting rotations. A direct read system also doesn't care what size tire you are running, but being that Subaru's chosen system is basic it doesn't tell you what tire is low with out a diagnostic tool, just that there is a problem via the TPMS dash light.

How the sensors work(Schrader type/Subaru).The sensors are awakened by the tires rotation. At about 15-20mph there is enough centrifugal force for the sensor to be awakened and start transmitting a pulse via RF to the TPMS module, letting the module know that the pressure in the tire. As far as the TPMS module is concerned, 26psi is the magic number. As long as all the sensors are sending a signal of 26psi or more the TPMS module will keep the light off. If one or more sensors transmits a signal of 26PSI or less then the TPMS module will trigger the TPMS dash light to come on. There is no way to read what the TPMS sensor reads for air pressure in the tire with out the use of a hand held TPMS read/learn tool or the Subaru Select Monitor III laptop(SSM3), IE: there is no way to get that info via your dash.

Yes, the TPMS sensors are powered by a self contained(none replaceable) battery, when it dies you buy a new sensor. When you come to a stop there is no longer the centrifugal force required to keep the sensor awake and they go into a standby mode. After roughly 10-15 minutes the sensor goes into a sleep mode and shuts off to extend battery life. Battery life is estimated at roughly 100,000 miles of use(according to Schrader).

If a battery in a sensor dies, a sensor goes bad or the TPMS module for what ever reason loses the programed IDs of one or more of the sensors it will trigger the TPMS light.

EDIT: Some have reported that while being at dealers having theirs sensor IDs reprogrammed to the TPMS module, the dealer/tech has asked what trip point(psi) they would like the TPMS system set to, implying its programmable. Which it probably is, I have seen the TPMS screen on the SSM3 laptop and it appears to have access to all of the TPMS functions and trouble codes. However being that TPMS is Federally mandated I am assuming it is a no no for them to play with any functionality settings of it.


Current(7-04-08) part number for a replacement sensor from the Schrader-Bridgeports site is: # 28203 for Subaru OE # 28103AG01A

Looks like you should concider replacing the sensors with your 2nd set of replacement tires.

 

And from cars101 I found 10 years approx 100,000 miles

Subaru Tire Pressure Monitoring System operation

exert below;

How it works:

When the car is turned on the warning light on the dashboard will come on for about 2 seconds. This is normal.
If the light flashes (3 seconds off, 1 second on), that indicates a problem with the system. Contact your dealer.

Each sensor has an separate ID code. When the vehicle goes 7-20 mph, a roll switch inside the sensor turns on and the sensor starts to take measurements every 30 seconds, and sends the results about once a minute to a receiver module under the carpet by the drver's door. The sensors are off when there is no motion (or 15 minutes after stopping).

When a low tire (app 26-27psi) is detected a warning light in the dashboard turns on. The warning light turns on, it does not flash.
The light does not indicate which tire is low, so please check all tires.
A blow-out won't show up right away.

When the vehicle stops moving for 15 minutes, the sensor enters 'sleep' or off mode to save battery life.

WHERE? A transmitter with a tire pressure sensor is located inside the each tire's air valve stem. It is designed to detect low pressure only (not high or over-inflated).
The sensor contains a battery. Battery life is 10 years or 100,000 miles. When the battery fails the sensor must be replaced.

 

That is not a bad battery life you guys are reporting. Other manufactures (such as Porsche) have sensor lives that are much shorter. Thanks for all the good info!!!

 

Forgt to mention after the TPM indicator started flashing I pulled into a rest stop to check tire pressure. All tires checked out to be at specified pressure. No low pressure here just a flashing TPM indicator light flashing.

 

Mine had been doing that for a few weeks. In the service manual it says that flashing 25 times and then steady on means a tpms unit failure. That's what I had. I went to the dealer last week and they found two defective units in my is 14 month old car. I did put third party wheels on my OB about a year ago, so the dealer blamed America's Tires for the problem. Maybe yes, maybe no. But the dealer paid for one under my warranty and I had to pay for the other. One unit plus labor was over $150. Ouch.

 

My original 07 TPM batteries in my Toyota just crapped out this summer. Keep in mind like all batteries extreme heat or cold temps can shorten life also.