Tire pressure light on...but pressure ok

[Mustang5L5]

My first real day driving my new (to me) '06 G35x On the highway doing 65MPH and the low tire pressure light comes on. Outside temp was right at 32 degrees. I figured the cold weather caused the pressure to drop in one tire. I get home and check the pressure..all in the 30-35PSI range. I drop them to about 32PSI (warm). Went for a drive and the light is still on. Anything else I should check before I bring my 1 day old car in for service? I kinda want to drive the car...so i may wait a week or two before actually doing so, so it gives me time to try some things. Is this common? Does cold weather or rain play a roll? We had heavy rains the night before that I drove in and the temp then dropped to below freezing during the night.

[TroysG]

as soon as I swapped my rims about 20-30 mins into every drive going above 60 mine comes on... first time it came on I freaked out pulled the car over checked each tire. and as soon as I turn the car off and turn it back on it's off... if yours is staying on you may have a faulty sensor

[Mustang5L5]

Guess i'll have to take it in then if it doesn't go away shortly

[Mustang5L5]

Ok, did a little more poking around.

My car has a full size spare. Basically it's a 5th OEM wheel in the trunk. I guess when the previous owner got new tires, he put one wheel in the trunk, used the spare and bought 3 new tires. I bet when i check the date codes in the AM, i'll find 3 are newer.

Anyway, does the full size spare carry a TPMS? I found the spare had a nail in it and was completely flat with 0psi in it. I plugged the spare and will fill it in the AM.

Does the car read the pressure in the spare if it's the full size??

[uf20wop]

usually cold weather will set it off, should go off when the tire warms back up

[uf20wop]

sometimes it takes a while to turn off though

[Mustang5L5]

Well it still hasn't gone off.


Does the full size spare have a sensor? I'm convinced one of my wheels is the spare tire and now the priginal is in my spare tire well.

I just have no idea how to tell which one was the spare wheel though

[jin22gt]

its the cold weather messing with your tire pressure light, had the same problem but it went away.

[gary c]

You need to keep the recommended pressure in your tires (35 to 37 PSI) cold.
Only then will you know if one of your sensors is defective. You should be
able to look at the stem on the spare to tell if it contains a TPS....or not
Gary

[Coach]

Originally Posted by uf20wop

usually cold weather will set it off, should go off when the tire warms back up

Cold weather doesn't set it off, low pressure does.

Tire pressures drop about 1psi for each 10 degrees F in ambient temperature, so if your weather has gone from 80F to 40F,
your tires are probably low by 4psi not just before you drive, but all the time. That's not the temperature messing with the
sensors, the tires are actually low, and driving alone won't bring them up.
Your tires will increase about 3-4psi as they heat up after you drive on them regardless of the temperature or pressure that they start at.
If they start at 35psi cold, they'll increase to maybe 39psi when hot. If they're at 31psi because it's 40 degrees colder,
they'll only get up to 35psi from driving, which means you're still 4psi low even when they're hot.

To the OP: If you measure your pressures cold and they're up to spec and you still get warnings, you might have a bad sensor. If you dropped them to 32psi warm as you said, they're probably well under 30psi cold.

[Mustang5L5]

It was something different.

It was because i was driving on the spare. I was right, the original owner took the full size spare out of the trunk, put it on the car and then bought 3 new tires. The original is in the trunk with a worn tire.

I took it out, swapped it withthe spare tire (the cleanest wheel withough a nick on it) and the light went away after some driving.

The spare also has a TPMS sensor on it.

My options:

1 swap tires between the spare and the one with the registered TPMS. My "spare" tire is worn, so i'd like to replace it anyway.

2 have the TPMS reset to the 4 wheels on the car....replace tire on new spare at my whim.

[Wannabe6MT]

Mine went off when i just accelerated onto a freeway in the rain. Got a little slippage and it turned on.

I thought somthing broke at first haha

[g3fly]

do all g's come with the TPM? because i had a flat and had to drive it about 1 or 2 miles and my light never came on. i got a 03 coupe m/t

[fbpem1]

Originally Posted by g3fly

do all g's come with the TPM? because i had a flat and had to drive it about 1 or 2 miles and my light never came on. i got a 03 coupe m/t

03 was the year it was optional and maybe very early 04. Same with the FX

Wannabe6MT, what probably happened to you is the tires were reading the rear and not the fronts since you were spinning and tripped the code because the other two in the front wern't going fast enough.

As for the trunk full size spare yes it is has a monitor in it, but it does need to be reinitialized to work, if you move your wheels and tires around you should always have them reinitialized. I do every car i work on, some are more sensitive than others to that (read: m's and 09+fx's) The G's will be fine but if you do have your spare wheel on there, and the original wheel in the trunk the tpms light will be illuminated since you have 1 tire on there that isn't registered to the bcm, the one that is registered isn't sending off a signal that the bcm recoginizes, becasue its not moving so its not giving off a reading. wow that was long winded.

[Mustang5L5]

Originally Posted by fbpem1

As for the trunk full size spare yes it is has a monitor in it, but it does need to be reinitialized to work, if you move your wheels and tires around you should always have them reinitialized. I do every car i work on, some are more sensitive than others to that (read: m's and 09+fx's) The G's will be fine but if you do have your spare wheel on there, and the original wheel in the trunk the tpms light will be illuminated since you have 1 tire on there that isn't registered to the bcm, the one that is registered isn't sending off a signal that the bcm recoginizes, becasue its not moving so its not giving off a reading. wow that was long winded.

Yup, now i have to decide.

Pay to have them reinitialized, or pay to have the two tires swapped because i want to put the nice brand new "spare" wheel back in the trunk in case i ever damage a wheel.