I noticed that earlier in the winter, when I left my car outside all night, when I went to drive it in the morning when it was cold, the tire pressure light would be on. It would go away after driving on it for a while. This actually happened to both me and my friend who has the new Saab 93. Plus, when I went to Enterprise rent-a-car in January, they said the same thing was happening to all of their cars with the tire pressure sensors.

I think it's what the previous posters have said - the sensors detect a difference rather than the actual tire pressure. The cold caused the air to compress, possibly at slightly different rates, and after driving a bit and heating the tires up, the air pressure went back to normal.

 

correct, they do detect a difference. even if its only in one tire.

however, the light isn't supposed to come on unless there is a difference of 15psi or somewhere around there.

I noticed my issue started after lowering the car too.

 

15psi?? that's like half the intended tire pressure. pretty bad...

 

i don't know exactly but its somewhere around there. basically, its not supposed to come on until the tire is dangerously low. 25 psi is not dangerously low.

also, having different tires/sizes might affect it to, since i'm pretty sure the sensor calculates by wheel rotations. eg. traveling at a given speed, a larger diameter wheel (ie. tire more inflated) will rotate less times than a smaller diamter wheel (flatter tire)

 

don't forget i believe the spare tire has the tire pressure sensor on it also. Actually i was told it does.

 

I was talking to some of the guys at work and apparently if the TPS light is flashing at you then there is a problem with the system. One of the problems is one or more of the sensors is not active and you need to "wake" them up, you lower the psi rapidly by 5 or more thus making the sensor react and wake up, a flashing TPS light might be more than that so I would bring it in to the dealer. I am not sure if this is 100% true or not, anybody have any input?

 

Spare does not have a sensor in it, not the tC anyways

 

^yeah i didnt think it would because its a spare, its not meant to be kept on the car for a long period of time.

 

cars like most highlanders, sequoia, land cruiser are the ones that do have a sensor in the spare. Basically the toyotas that have a full size spare have a sensor in them

 

it was a guy from toyota that told me there was a sensor on the spare. i was in an accident with my xb2 afterwards i had the same issue of the light being on.

 

I had same thing happen with the light and the pressure change in the tires worked thanks.

 

... this thread was dead.

FYI the posts in the begining were true about the diameter of the wheels.

the 07+ sensors actually read the pressure, do not use fix a flat or anything like that or you'll need a 150 sensor on top of a tire.