TPM Problems

paul champion · Apr 11, 2012

I have a 2006 997 CS fitted with TPM. Now the manual states that for 19 " summer tyres the pressure should be 2.2 bar front and 2.7 bar rear. However, I have checked that the on board computer menu settings reflect these tyres, and when the computer checks the tyres from cold, they show 2.1 bar front and 2.5 bar rear. It does not state to add air, if anything it shows the front as + 0.1 bar! Which is correct? I have taken it to Porsche Silverstone, who reported no faults via diagnostic check, and that the manual maybe wrong and go by the on board computer, if there was a problem it would show 'add air'. Is it just me or is there something wrong here? Thanks.

Nick_USA · Apr 11, 2012

ORIGINAL: paul champion

I have a 2006 997 CS fitted with TPM. Now the manual states that for 19 " summer tyres the pressure should be 2.2 bar front and 2.7 bar rear. However, I have checked that the on board computer menu settings reflect these tyres, and when the computer checks the tyres from cold, they show 2.1 bar front and 2.5 bar rear. It does not state to add air, if anything it shows the front as + 0.1 bar! Which is correct? I have taken it to Porsche Silverstone, who reported no faults via diagnostic check, and that the manual maybe wrong and go by the on board computer, if there was a problem it would show 'add air'. Is it just me or is there something wrong here? Thanks.

Because the TPM also takes into account the outside temp, tyre temp and barometric pressure

Rodney Naghar · Apr 11, 2012

As above. The correct pressure should be set at an ambient temperature of 20C, not the lower levels we're currently experiencing.
So the sensors are estimating that at 20C the pressures would be correct, otherwise your tyres would be overinflated.

garyw · Apr 12, 2012

ORIGINAL: paul champion
they show 2.1 bar front and 2.5 bar rear.

Thats exactly what mine shows when starting the car...
I wrote about it in the Porsche Post register column as mine has stated to add air as the air temperature had started to rise slightly..

garyw

Geoff_Fields · Apr 12, 2012

Just a thought here guys, but that must be calibrated to estimate for air. So what if you fill with Nitrogen, which has a much lower rate of expansion?

paul champion · Apr 12, 2012

Thanks for your replies - so when the outside temp is about 20 C, that's when the on board computer should show tyre temps as per manual i.e. 2.2 bar front and 2.7 bar rear?

Nick_USA · Apr 12, 2012

ORIGINAL: paul champion

Thanks for your replies - so when the outside temp is about 20 C, that's when the on board computer should show tyre temps as per manual i.e. 2.2 bar front and 2.7 bar rear?

Correct assuming you haven't driven the car ie the tyres are warm.

Lancerlot · Apr 12, 2012

Paul,

The recommendation is for tyre pressures to be checked at an ambient temperature of 20deg. C.

Lower temperatures will produce lower tyre pressures, so you may need to make allowances for this.

I tend to regard the TPM as a guide only and find it most useful for alerting me to the possibility of a puncture when on the move.

For accurate measurement, I normally use a good quality analogue gauge with 0.1 bar graduations.

There's quite a bit on the forum about the use of nitrogen fill rather than air. It does reduce fluctuations in pressures and seems to maintain those pressures for longer.

Regards,

Clive