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I have a Cayman and a Cayenne. Called the dealer today about the Cayenne and told him that the pressure on the front left wheel was reading -2 on the OBC and was throwing the warning light. He told me that I needed to add two more pounds to the tire and then the OBC would read normal. I said, "hold on a second .I just read the pressure (with a tire gauge) in the tire and it read correctly as stated on the inside of the door. He said I get this call almost everyday..just fill it up 2lbs and the light will go off..."the tire pressure monitor system is more accurate than the gauger" So I used another gauge and would you believe the same result as the first gauge. The dealer confirmed it was the same system in the Cayman. Which reads low in comparison to my tire gauge's. Any thoughts on this matter?
My interpretation reading the manual is that the TPMS is a reference point and not a true reading.
TPMS
TPMS - The Tire Pressure Monitoring System provides early warning of any drop in pressure by continuously monitoring the pressure in each tire and alerting you in the onboard computer display in the event of a pressure deficiency. It communicates the exact pressure of each tire and/or their deviation from ideal pressure. This does away with the need for regular air pressure checks at the service station, which often prove highly inconvenient.
There are about a zillion explanatory posts on the TP Monitoring System on the site. Your are correct - it is not to be used to measure but monitor air pressure. Dealer service writers and/or sales people seem pretty confused about this. That said I'd check to make sure the tire didn't have a slow leak even if your guage didn't show it. Temps, barometric pressure and other factors could be at play as well as a slow leak. I'd check to make sure the tire didn't have a slow leak even if your guage didn't show it yet. Normally if only one sensor is showing a difference then a small puncture could be present. But -2 is well within expected diffferences as well and usually does not throw the indicator light. Please do read some of the previous posts that explain why there is a difference.
Like your salesperson told you, this really is a common question.
The TPMS will never match the reading of hand held guage because they deliver two different types of measurements.
When you read tire pressure with a guage, you are reading a 'relative' pressure. That's the pressure difference between the inside of the tire and the outside (the atmosphere). Most hand held guages are calibrated to read most accurately at sea level.
When you read tire pressure with TPMS, you are getting an absolute pressure because the sensor is inside the tire and it can not see or feel the atmosphere.
Because of these two different styles, the two will likely never match because the atmospheric conditions are always changing.
TPMS
TPMS - The Tire Pressure Monitoring System provides early warning of any drop in pressure by continuously monitoring the pressure in each tire and alerting you in the onboard computer display in the event of a pressure deficiency. It communicates the exact pressure of each tire and/or their deviation from ideal pressure. This does away with the need for regular air pressure checks at the service station, which often prove highly inconvenient.
Thanks to both of you for the reponses. If I understand Gator Bite I should use the TPMS as the gauge and ignore the hand held guage?
TPMS
TPMS - The Tire Pressure Monitoring System provides early warning of any drop in pressure by continuously monitoring the pressure in each tire and alerting you in the onboard computer display in the event of a pressure deficiency. It communicates the exact pressure of each tire and/or their deviation from ideal pressure. This does away with the need for regular air pressure checks at the service station, which often prove highly inconvenient.
No. Always use the hand held guage (be sure and get a good one - this one is one Beez put me on and is handy for where you and I live because it can be set for local altitude Pegasus - Intercomp 2.5" Liquid Filled Tire Pressure Gauge: 0-60 psi) to check the pressures and air up the tires and the TPMS to monitor them. The Owner's Manual actually says that somewhere.
TPMS
TPMS - The Tire Pressure Monitoring System provides early warning of any drop in pressure by continuously monitoring the pressure in each tire and alerting you in the onboard computer display in the event of a pressure deficiency. It communicates the exact pressure of each tire and/or their deviation from ideal pressure. This does away with the need for regular air pressure checks at the service station, which often prove highly inconvenient.
Thanks again...its getting alot clearer..must be the altitude or something. Santa Fe do you know what the correction factor is for our altitude vs sea level? I didn't consider that guages needed to be corrected for altitude.
Thanks again...its getting alot clearer..must be the altitude or something. Santa Fe do you know what the correction factor is for our altitude vs sea level? I didn't consider that guages needed to be corrected for altitude.
Just buy the Intercomp (think of it as a present for your P cars) and follow the instructions in post #10 here: Clearing TPMS error messages. Then you will be ready for all altitudes with no thinking required...
I've had mine going off lately too. Even weirder, on one screen (that shows how much they're off), one rear wheel says '-4' and the other says '-2'. HOWEVER, on the other screen (which shows the actual pressures), both rear wheels show the same reading.
So what's the deal here? Depending on which screen I'm on, TPMS actually says different things. Is the error on the computer side of things? Who knows.
TPMS
TPMS - The Tire Pressure Monitoring System provides early warning of any drop in pressure by continuously monitoring the pressure in each tire and alerting you in the onboard computer display in the event of a pressure deficiency. It communicates the exact pressure of each tire and/or their deviation from ideal pressure. This does away with the need for regular air pressure checks at the service station, which often prove highly inconvenient.
I've had mine going off lately too. Even weirder, on one screen (that shows how much they're off), one rear wheel says '-4' and the other says '-2'. HOWEVER, on the other screen (which shows the actual pressures), both rear wheels show the same reading.
So what's the deal here? Depending on which screen I'm on, TPMS actually says different things. Is the error on the computer side of things? Who knows.
Mine did that when it was new. I just went through the procedure for resetting and reteaching the whole thing (procedure is in the manual) and that problem has not returned.
Reset it about three times, with the problem recurring.
Strangely, it would be good after I reset it, then RIGHT when I would turn the key off, it would 'fault', and continue to report low pressure when I restart the car. Then it just quit doing it. Clearly a computer issue to me.
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