Low Tire Pressure Indicator

The low tire pressure indicator on my 2009 2.5i SE is illuminated. I've only had the car about a month but I figured that, since the temp has dropped from 75+ when I got the car to 10-40 degrees now, that the low pressure was just a result of the temp drop. It has been generally on, but is occasionally not on, for the past week and I'd been meaning to top off my tires and double check their pressure.....

 

I finally got to checking my tires today and found that they were 29 to 31 psi and the door jam sticker calls for something like 32 or 33 in the front and 30 or 31 in the rear as I recall. With these pressures the light was illuminated. I raised the pressure to ~34 all around since it was relatively warm at 40 degrees today. After inflating to 34 I still have the indicator lamp illuminated.

 

Is there a certain amount of time that the system needs to see that the pressure is adequate?

 

What pressure causes the indicator to illuminate? I was surprised to see that it was lit and my lowest pressure was 29+..... I figured that it would have to be 25 or less roughly to cause the light to come on.

 

Is there something that needs to be done to reset the illuminator?

 

 

Thanks

 

Bryan

I think it triggers at 29. You'll need to drive a while (couple of miles maybe) before the light goes away.

make sure your pressure gauge is properly calibrated? (I know...who calibrates a $5 tool) The only thing I can think of one of them is reading off. The TPMS is really finicky for me too.

You sure? There are a lot of threads that say only a Subie dealer can re-set the low pressure indicator lamp for, $50.

 

IIRC, nothing on the aftermarket yet.

27 psi is what triggers it.

You sure? There are a lot of threads that say only a Subie dealer can re-set the low pressure indicator lamp for, $50.

 

IIRC, nothing on the aftermarket yet.

 

 

I wasn't talking about the TPMS, I was talking about the little gauge he bought at Autozone or wherever that checks the pressure of the tire from the outside.

I've actually got a $15 gauge It's one of those big round dial gauges that measures 10 to 50 psi so it's pretty easy to get a good reading. I assume that it's accurate, at least as accurate as I need for filling tires. I can't think of ever hearing of anyone calibrating a tire pressure gauge

 

I'll have to go for a drive and see if it turns off. If not I'll pump my tires up to 38 psi or so and see if that helps. I'd be surprised if I had to have Subaru reset it but I've heard of stranger things....

 

Stay posted....

I've actually got a $15 gauge It's one of those big round dial gauges that measures 10 to 50 psi so it's pretty easy to get a good reading. I assume that it's accurate, at least as accurate as I need for filling tires. I can't think of ever hearing of anyone calibrating a tire pressure gauge

 

I'll have to go for a drive and see if it turns off. If not I'll pump my tires up to 38 psi or so and see if that helps. I'd be surprised if I had to have Subaru reset it but I've heard of stranger things....

 

Stay posted....

 

 

You shouldn't need to have Subaru reset anything. Actually I had the same issue just a couple of weeks after I bought my car. They claimed the TPMS was very sensitive to temperature. I haven't had an issue since that first month.

 

Eric

27 psi is what triggers it.

 

the manual i thought says over 10% below factory PSI. (isn't factory 35psi?, never looked)

My factory pressures were 33/32, or 32/31. or something VERY close to that.... it's snowing outside so I'm not going to run out and check again but I'm sure I'm close.

 

Anyway, I went out and started her up and the light was on. After 20 minutes of driving the light turned off..... I ran in the store and came out a bit later and drove home and the light was still off. I guess it's really just that sensitive and takes a bit of time to reset.

 

Thanks for the input everyone

I have the same problem. I think it is very sensitive in cold weather. Every morning it is on, 33 degrees and lower. After I drive it, the light warning disappears.

Woodstock - that might be because your tires heat up and the air pressure increases with the heat.

yeah, i know that heat increases air pressure, and cold decreases air pressure right?

Once the issue that is causing the TPMS light to come on is taken care of it only should take a couple miles of driving for the light to go out.

 

It is in the owners manual.

Hurrah! Some by-god actual physics that someone got right! (Hey -- there's so much wrong physics tossed about here, you've got to give credit where it's due.)

 

The TPMS system seems to be slow to respond to changes -- for example, before we got ours reprogrammed to recognize the new wheels (with new sensors), it took about 15-20 minutes of continuous driving for the system to recognize the fault and start the light flashing. It wouldn't be surprising if it took a while to recognize that low pressure has been corrected.

 

Now, although Subaru dealers are the only people who can reprogram new sensors into the computer, most tire places seem to have the ability to reset the computer -- so if you take a low tire somewhere and get it filled, they can get the light off quickly. But if you do it yourself, you're at the mercy of the system.

 

This is one of those things I'd like to smack everyone in Congress with a pie in the face for. What a PITA. HPH

It's based on MPH if IIRC. Once you attain 25MPH the system activates. If tire pressure is low, it will trip the light. In order to reset the light, you must fill the tire to the propper pressure and drive at >25-30MPH for a few miles to reset it.

My Friends 08 Forester had its TPMS light go off. When I checked the pressure, it was down to 26psi in all 4 tires. I filled them all up to 32 PSi, and the light went out almost instantly. I dont think you have too much to worry about. Seems like your car is under warrenty in case you have a faulty Sensor.

Once the issue that is causing the TPMS light to come on is taken care of it only should take a couple miles of driving for the light to go out.

 

It is in the owners manual.

 

exactly. Just check when you have time to make sure you are not running on flat tire, besides you can probably feel it if u are running on flat tires:lol:

yeah, i know that heat increases air pressure, and cold decreases air pressure right?

 

Yeah but you said after driving a bit the light would turn off. Once the tires warm up the pressure increases and turns off the light.

All you have to do is set the tire pressure to the right pressure and drive it 1-2 miles and the TPMS light should go out on its own. If it doesn't they may need to be re-calibrated/initialized. Of all the ones I see 99% of them go out on their own once the tire pressure is correct and it is driven 1 mile. Not sure where the 25 mph comes from but I have reset a few while driving in the dealership parking lot at 10 mph.

There was a link posted somewhere on here that went to a "Drive" article explaining the TPMS system and how Congress was requiring it. It mentioned there was a min speed (IIRC 25mph) that the sensors would start emitting a signal, then it would send a signal in increments. It also mentioned the pressure that set them off... I'm just too lazy to search.... search TPMS and you'll get a lot of info.

 

As for the air thing it's simple Boyle's law.... PV=T assuming Volume, V, stays constant and temperature, T, drops, pressure,P, must also drop by the same proportion and vise versa.

 

I agree the damn TPMS is a PITA and very finicky on the Subarus. Since the car is new just go to your dealer, tell them your problem and ask them to fix it..... it should not cost you a cent as you are still covered under warranty. Chances are they'll check the pressure and reset the light, problem will be fixed till next winter.

 

Best of Luck

Be lucky it isn't like Toyota's where the spare tire has a sensor as well and if you put too much air in it, that will set the light off as well.

Be lucky it isn't like Toyota's where the spare tire has a sensor as well and if you put too much air in it, that will set the light off as well.

 

the SPARE?.... even if it's not on the vehicle?...

 

we live in a nanny state anymore, and it's getting worse. pretty soon we will have to have a valet open and close a door for us.. we may catch a finger in the door if we do it ourselves.

 

(like my Dad did with a 2009 Z06, lol)

my Subaru dealer offers to fill your tires with nitrogen.. it isn't influenced as much as just air. for only $40! LOL

*isnt influenced as much as air is by temperature change