Hey guys,

I was driving this weekend on the highway for over 300miles at a time (see post about 21.56mpg) and two times the tire pressure sensor came on. Once on the way there after 250 miles, and once on the way home after about 130 miles. I just got to my destination, turned off the car, turned it back on and the light cleared. Any ideas? I think the tire pressure is good to go as I could not check them accurately since the tires were warm from driving, but I am going to check them tonight as they've been sitting for 4 hours. I'm just curious if anyone else has seen this problem. Let me know your thoughts, as I haven't seen any TSB's about this. Let me know.

Is there something I'm missing? Is this normal operation, because of driving long distances? Just trying to find out some info before I take into the dealership to have them look at it!

 

When you check your pressure, check the spare (if full size) because it has a sensor too. I scratched my head with the sensor going off when the pressure was fine on all 4... then I remembered the spare.

 

WHAT? not to be a jerk, but I'm totally skeptical that the safety pressure sensors would monitor a tire that's sitting idle in the trunk. Anyone have ideas, the tire pressure seems to be within specs and the sensor only came on after driving a long distance on them both times. The sensor then went off when I turned the car off and turned it back on in park and did not come on again after the second time. I'm just curious to find out what's going on before I take it into the dealer.

 

Not to be a jerk, but if you don't want to check the pressure of your spare tire to rule it out, then you must not want help. I have seen the tire pressure sensors and they are simple transmitters. The spare tire DOES have one as well if it's full sized. When mine was going off, it was driving to the mountain a couple of months ago and it was pretty cold. Once we got back down to where it was warmer, the sensor wasn't on anymore. I checked pressure of all 4 and they were fine.... then I checked the pressure on the spare and it was a pound or two above the sensor trip mark. Cold= lower PSI so it went off. Added a few pounds of pressure to the spare and went back to the mountain the next weekend where it was even colder and had no problems.

 

My manual says it monitors the pressure of all tires except the spare (p. 2-12). It doesn't distinguish between the donut and the full-size (that I have). I'm not sure why it would not be in the full-size spare, but it seems not to be. Anyone with better information? I'm curious. Thanks.

 

I think I read in the manual that the wheels have to be turning to some minimum speed before it'll send a signal and therefore be monitored.

 

Mine came on once, but the left front tire was a bit low. Went off as soon as I filled it.

 

I have a fill size spare in my X. I didn't know about the spare tire sensor either. I guess the only way to find out for sure would be to let the air out, then see if I get a warning as drive to the gas station to fill it back up.

This would be a nice feature since when the tire is in the trunk the valve stem is facing down which makes checking its pressure on a regular basis a pain.

 

Yes, the spare is very hard to check. I tried to find an extension to attach to the valve to bring it out into the trunk area so I wouldn't even have to dig under the carpet at all. I checked a bunch of stores and couldn't find such a thing.

Does anyone know of a source for one?

Thanks.

 

I don't work for Infinity or Nissan and can not definitively state what their TPMS logic is set up for. However, I did work at Ford and now Mercedes and was there whan the FMVSS requirements came in for TPMS. Neither Ford nor Mercedes monitor the pressure in the spare because that would require extra wiring and sensor pickup as well as logic to run the software. Way too much of an expense for the OEM. Infinity may be different but I suspect that it is not.
Since the FMVSS (federal motor vehicle safety standard) is not set up for a "live" system in the US until next year (06MY), most US manufacturers have chosen the low end TPMS model which works by a magnetic sensor telling the software logic how many times the tire rotated in a given distance. That signal is compared to a nominal and a low warning displayed if the values are more than what the nominal states (low tires rotates slightly faster than a full tires).
The other and more elaborate systems tell the software logic every so often what the pressure in the tire is (ever x number of revolutions). It is this system that is on our G35's. This is why you have to drive a little after you added air to the low tire to make the TPMS warning light turn off. I have found out that the tolerances in the sensors are not very accurate and that only a psi or two drop is required for some sensors to show up with a fault, and consequently only a psi or two is required to make the light turn off again. The best countermeasure is to inflate your tires to the exact manufactures pressure and drive for 2-3 miles. This should re-set the TPMS to the correct pressure and it can them more acurately (up to a point given the sensors limitation) state whether there is a low tire or not.
I know this is a little lengthy but what do you expect from a automotive engineer. Hope this helps.

 

I don't think mine has ever worked. I just replaced all wheels and tires and have no tire pressure snsors at all and my light has never come on. I went with 18x9.5 rear / 18x8.5 front SSR GT3 rims and have no problems. I did have a problem with the SRS air bag light staying on and found out how to clear it. It must have turned off the tire sensor too.

 

Good point about the spare, Mosi.

Check all the tires cold, and adjust to spec.

 

Okay... I know the 04 manual states that the monitor is not on the spare but I'm pretty sure it's a right and wrong statement. Right if you have a donut (mmm donuts), wrong if you have a full sized spare.

I took the liberty to show you guys how to tell if you have a sensor on your spare or not. The first pic is one of my re-powdercoated rims (dirty) showing the valve stem. The metal valve stem is attached to the sensor transmitter and is proprietary from what I understand. When the tire is off, you remove the metal sleeve/nut on the stem to remove the sensor. The metal sleeve/nut on the spare tire is an indicator that there is a sensor there.... 2nd pic.

 

The thing is, if the alert has gone off, even right after you add air, I noticed that it took about half a mile or more for the light to go off when I drove right after adding air!

 

Does anyone know how much the valve stems cost with the pressure sensor? I've seen the actual thing and they could break pretty easily if you get a flat.