Hello
I recently changed the steering wheel on my 2011 porsche cayenne for a sport steering wheel so I basically lost the Multi functions which were not a concern at first but how can I now correct the TPMS warning sign I am getting ? Is there a way to manipulate the MF via the radio setup ?
thanks !

 

Can't help with the stalk question, you might be outa luck there. But you can eliminate annoying TPMS messages by changing over to nitrogen in your tires. Not sure about your area, but it only costs $7/tire here.

//greg//

 

How does nitrogen affect TPMS message?

 

Ambient temperature affects tire pressure. As tires warm up, pressure increases. As they cool, pressure decreases. When pressures decrease below the TPMS threshold you've established, the system alerts you. What causes the rise and fall is the expansion/contraction if the O2 content inside the tires. When summer turns to fall turns to winter, the O2 in your tires shrinks

Nitrogen does not expand/contract to the degree of O2. Hence N-filled tires stay within the TPMS parameters that you have selected.

//greg//

 

I thought you meant nitrogen somehow can help OP reset TPMS warning.

Hence my original question.

Actually, I think it is actually the lack of moisture in nitrogen that help stabilize tire pressure.

 

Moisture is H2O. Without hydrogen or oxygen, there can be no moisture. Once N-filled, the tires contain pure nitrogen. Nothing else.

And except for the owner setting initial parameters, TPMS on the OP Cayenne is self-resetting. As soon as tire pressure returns to within parameters, alert is turned off. A proper full of nitrogen prevents it from coming on in the first place (except in the case of puncture/leak))

//greg//

 

You are correct. Moisture is water. But hydrogen and oxygen in tires do not react to produce water.

When you fill your tires with air, the compressor just draws ambient air, hence the moisture with it. When you fill with nitrogen, it comes from a pressurized cylinder and should be moisture free.

Also, all gas expands and contracts according to Ideal Gas Law. The size of the molecule, ie what gas it is, is irrelevant.

 

This is a horrible myth that I wish would just die. Unless your tires are mounted in a pure nitrogen environment (which for consumer cars isn't going to happen) then the nitrogen fill is just topping off the regular air that is already in there.

And the "over time it will push out the O2" line is BS too. As an ex-scuba tech diver I used to have an O2 gauge so I used it on a friend's tires when he was all into the hype over nitrogen fills. We measured from installation to removal of a set of tires that lasted 32 months and included one 2 pound (average across the tires) fill right about the 2 year mark. What we found was that after the install there was still 19.7% O2 in the tires. After the top off they were still at 19.6% and they were still at 19.6% when he went to get new tires. The best case tire was 19.5% and the worst case was 20.1%.

So the results were A) a "nitrogen" fill still ends up with a breathable air mix and B) the O2 didn't escape from the tires at a significantly faster rate than the nitrogen.

Yes over time you would eventually get to 100% nitrogen, but not in the life time of your average tire (e.g. not on a show car that is barely driven).

 

As to the original question however, I have not seen anything in the PCM that relates to the TPMS.

I don't know about the 958s, but in the old 996s I know it is a popular mod to replace the switch module that the stalks are on with the one that has the OBC and cruise control stalks. I expect you might need to do the same thing here. I don't know if that would require coding or not though (the OBC mod in the 996 does, but that's to enable the OBC itself and not specific to the switch module).

 

Gnat - you clearly haven't ever had your tires nitro'd. Mine was done on a lift (no weight on the tires). The professional system then gets connected to all four tires simultaneously. Once it's started, the contents of the tire are evacuated. Once negative pressure is detected (drawing vacuum), the system switches over. It then starts pumping bottled nitrogen to the pressure that was preset by the operator.

And pharmar - I answered your question. Once the tire pressure returns to within owner-established parameters - whether because the tires simply get warmer, or because you've added air pressure - the TPMS warning resets itself automatically. If it doesn't, you may have a bad sensor. The owner manual is reasonably straight forward about TPMS.

//greg//