So I park my car the other night and go out or whatever and come back a few hours later, turn on the car and the tire pressure light comes on. I drive it to my friends house and test the pressure in the morning and it says 21psi for all 4 wheels.

At this point i'm like wtf, so I use a different tester(same model) and it also tells me 21-22psi for all four.

As I'm going home the light turns off on the highway, I'm assuming because of the friction/heat. I wait until the next morning startup while its cold and the car and the light hasn't come on yet.

Anybody know what the deal is? Its a 2010 with 7000 miles.

 

You're about 11psi low on all four tires.

 

tire pressure has to be 32 psi

 

Should be 32 in the front and 29 in the rear...

And those pressures should be measured on "cold" tires... Before you drive on them.

 

Alright, I'll fill it up to those specs, I know tires leak air, but is it normal for all them to be exactly 21-22psi?

 

Yeah, tires lose air. If they sit or hit a bump wrong they will lose air. However, all at once? Not likely. I've had people tell me that they used "their" gauge to put air in so either you put the wrong amount in based on a faulty gauge or somebody is screwing with you.

 

You asked WTF is up with the sensor.
Your car has been asking WTF are you driving me on 21 PSI !?

 

If your tires are "losing" air or leaking at all, you have a problem. The only time the pressure should change is with the temperature. If it is cold out, the pressure goes down a little. If it is hot out (or your were just driving on them) the pressure goes up.

But no matter the case you should NOT be running at 21psi, ever. Even on cold tires. The recommended 32/29 pressures are supposed to be measured "cold" ... without driving on the tires.

Whaaat? Your tires should not be losing air. That's why they have a seal around the wheel. The only pressure change is from temperature - like I said above. If you're "losing" air, you need to get it checked for a leak.

 

Air will leak right through the rubber at a rate of a few PSI per month and the funniny thing is that as you add more air over time it will leak less and less BECAUSE the smaller molecules in the air will leak out first leaving the larger molecules of the gasses composing the air we breath in the tire like "Nitrogen" which has a hard time leaking through the rubber. This is why some service centers use Nitrogen to fill the tires . . . it's a big molecule (atom) so it leaks less.

 

how cold is it where you are?

if it's like freezing temperatures, then the pressure can drop low enough to cause the TPMS light to trigger.. if it's not freezing.. then you just suck and need to fill up the tires to the right pressure.

 

He's in Florida . . . I don't think it is cold there yet. It's a new car and the tire pressure was probably low to start with or it just leaked out over the few months that he has had the NEW car.