rmklaw

Suddenly my TPMS says -4 warning on tire pressure. I measured all tires with two accurate (racing analog and a digital) gages and they show on all tires that the TPMS reading is 8 pounds less than the actual tire pressure.

The dealer says that PCNA has instructed them to use the TPMS readout to fill the tires, not any gauges. This would cause the tire specifications to be exceeded (rear full load would be 52 pounds when TPMS indicates 44).

Has anyone heard of such instructions to the dealers? Seems that PCNA would be buying itself a huge liability in case of a blowout plus the car would ride like a no shocks rock. Thanks.

jnx

I don't think you are to use the TPMS for that purpose. I believe it states something like that in the owners manual. You may want to look it up and show it to the dealer. My TPMS is off when compared to my gauge. I would go with the gauge reading.

rmklaw

I agree with you. However, I am getting random low pressure indications in diferent wheels at diferent times.

GSIRM3

Mine reads about 2 psi lower on all four tires than what my gauges indicate, but I am not getting alarms since the 2 lb difference is within the allowed variation in the computer.

boolala

If TPMS on the p-car is anything like the Benz the actual reading is not pertinant. All it cares about is changes in tire pressure from the time your re-synchronize it and effectively tell it what the "normal" pressure should be.

Having said that the TPMS in my Benz is spot on with guage readings.

GSIRM3

I think the TPMS in the 997 is different than the one you described in your Benz, and definitely different from the one in my M3. The M3 TPMS did not actually measure tire pressure. It measured difference in rotational speed between tires on the same axle. Therefore, once you set your pressures and resynchronized the system, it doesn't care what the pressures are unless one of the tires loses air.

However, the TPMS on the 997 appears to have reference values for tire pressures in the computer based on full or partial load of the vehicle, and size and type tires (summer or winter). The computer compares air pressure as given by the TPMS to the values in the computer and will alarm if the "actual" values as given by the TPMS are not within a specified variance of the values in the computer. Therefore, if the TPMS is not accurate, it can cause alarms if tires are inflated to the "correct" pressure as measured by a good tire gauge.

PAULSPEED

Hi,
Could be the batteries are running low in the sensors. Just
a thought.
Paul

99firehawk

set the presures and re set the system drive it for 15-20 minutes and it should recalibrate

rmklaw

I did. Still same problem. Porsche said to have dealer check unit. I have to take it in anyway for a bigger thing... clutch change (9K miles).

jw1977

I've had the exact same problem. In my case my gauge reads 3 pounds higher than the tpms. I finally just increased the pressure in the fronts to stop the alarm from going off so now i run 36/39.

Musclehedz101

Ok, this just started for me twp days ago and can not get warning to go away...what as the "fix" for you?

Mussl Kar

Black tape over the warning readout. Had mine turned off by my tuner.

Chris from Cali

Funny you ask - I just topped up my tires a couple days back and the TPMS is VERY accurate - +/- 1 psi on all tires.

Musclehedz101

Tried post #13 from here https://rennlist.com/forums/997-forum/377294-tpms.html and it has worked...so far!

ADias

Correct! TPMS gen 2 in the 997.2 is accurate.