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I just bought a new 2011 Honda Fit and while driving it home from the dealer, I noticed that a little light on the dashboard was on that said "TPMS". When I got home, I consulted the owner's manual and learned that this acronym stands for "Tire Pressure Monitoring System", and that the light being on indicates that there is a problem with the system. (There is a different indicator that comes on if the pressure in a particular tire is low.)

The actual tire pressure was fine and there was nothing visibly wrong with the tires, so I called the dealer to ask about the indicator light and was told that it is fairly common for the TPMS sensors to malfunction in cold weather, in which case they just need to be reset by the dealer. I'm scheduled to take the car back to the dealer this week anyway to have some options installed, but since this is a brand new car that I'm most likely planning to keep for a very long time, I'm curious whether this really is a common and trivial issue or if it's something I should be concerned about and push to have fixed. I live in Colorado and while it was indeed chilly that day (I believe it was around 25-35F), it is certainly not unusual for it to be that cold or colder here many days per year.

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Did you test the tire pressure right after you got home or did you let the tires cool completely? If the tires weren't as cold as they were when you started your trip you're probably getting a higher reading than the car did via the internal sensors. That is to say the pressure could legitimately be low due to the cold. –  Mike Deck Mar 16 '11 at 4:59
    
@Mike I did test the pressure right away, so you might be right there, but that particular dash indicator doesn't mean the pressure is low; it just means there is something wrong in general. –  Tim Lara Mar 20 '11 at 20:09
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I don't know if it's common for them to malfunction, but assuming there are no leaks in your tire the pressure at 25F is about 10% lower than at 70F which is probably enough to trip the sensor.

I have a BMW with TPMS and any time the temperatures drop quickly the light comes on my dash. If the temperature drop is temporary and things warm back up later in the week the light will often go off on its own. If that's not the case I usually top off the tires with air and that also resolves the issue.

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The dealer reset the TPMS system and so far the light hasn't come back on. I'll have to see if it happens again the next time we have a cold snap. –  Tim Lara Mar 20 '11 at 20:11
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The TPMS in my 2008 Subaru Forester uses sensors attached to the valve stems. The OEM part number is 28103AG01C. Each has a built-in radio transmitter, operating at 315 MHz, powered by an integrated battery that sends coded signals to a received in the car. The sensor also has a motion detector, and shuts down when the wheel isn't moving, in order to save battery life.

Either low tire pressure, or a low sensor battery condition, or lack of a signal from one or more wheels, will trigger the dashboard light. In very cold weather, the batteries integrated into these sensors have reduced performance, so they may trigger an alarm even if tire pressure is perfect.

It's always a good idea to check tire pressure periodically. If the light comes on when it is very cold, check tire pressures. If they are OK, wait for the temperature to warm up. It the TPMS light stays on, there is a system problem. One tire advisor told me that the batteries in these sensors last about 10 years, so if you have to replace one (and you’ve had the car for about 10 years, and plan to keep it), you may as well replace all four. The parts cost $40 to $75 each (so, times 4 for all 4 wheels), depending on where you buy it, plus installation labor, which requires unmounting and remounting each tire, so it isn't a cheap repair.

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