simplysql

Yesterday, the light on my wife's 4Runner indicated a low tire pressure - on hers, you have to check 5 tires (including the spare) to figure out which one is low - turns out her rt. front passenger tire was 2 lbs. low - so I filled it up, to 32 lbs., and the light went off. While I had the air compressor out, I figured I'd check the 997's pressure as well - although received no indicators from the TPMS on it. The fronts are supposed to be at 37 - rears at 42. The fronts were at 32, the rears were at 37 - so my question is, why didn't I receive an indication from my TPMS? Is the system calibrated differently than the 4Runner (which in my opinion is too sensitive!) - or do I have a problem that needs a checkup? Thanks!

MJones

What temps did the OBD indicate?
What was the ambient temp?

Edgy01

My TPMS reports absolute TP to me and only goes off if the delta is more than that,--not sure what the delta is that triggers it, but 5 psi probably isn't enough to do it.

simplysql

outside temp was around 50F when I checked it - I will have to check to see what that delta should be.

Bijan

Not sure if it applies to the 4Runner but apparently some systems are a differntial type, using the ABS sytem to detect different spin rate on an axle.
I am also not familiar with the Porsche TPMS system but is your measuring gauge accurate?

JFScheck

The TPMS on both my Cayenne and my 997 have NEVER given me an issue - set the tire pressure cold and drive around - in fact interesting as you drive how much the tires heat up. ;-)

Check the owners manual - you can change the points that it will go off - mine is on default.

On the Cayenne and my Jeep - both TPMS have indicated bolts (not nails but damn BOLTS) in the tires and mild leaks. Knock on wood - the 911 has yet to suffer such damage to her shoes...

Minok

The TPMS (at least on the 2009 997) takes into account the ambient temperature. So if the car is sitting with cold tires in very cold weather, the pressure will be less and correct, since, once the wheels heat on driving, the pressure will rise to the proper level. The key is to have the right temp on operating-temp tires. But you must measure and fill on cold tires.. so you have to take the temp effect on the air into account. The P TPMS supposedly does that. I think any gauge you use on the valve stem does not.. so you would have to do some math in your head, or you will end up with over pressure tires in the winter.

What the fronts and rears are supposed to be depends, of course, on if you have 18" or 19" wheels and even if you have summer or winter tires.