Planet 9

OK, Tuesday night I was driving from Arlington to Richmond, with a couple bags in the back (computer and overnight), and some conference giveaways in the front cargo hold (30 lbs total). I stopped for dinner in Fredericksburg. As I pulled in, I received a tire warning and the TPMS diagram showed the left rear at "-7". Went outside, tire looked fine, no flatness whatsoever.
(FYI, tires are 235/50-17 OEM Michelin Pilot Sports.)

Had dinner, came back. The car is started, then I receive the dreaded red "flat tyre!" warning, tire still at -7 according to TPMS. Still didn't look flat, but I decided to drive it to the gas station next door with the air hose.

Filling it for 20 seconds, no change in pressure shown after starting the car and waiting for the TPMS reset. Then I fill it another 20 seconds, and the tire shows up at 47 pounds! (8 lbs higher than the right rear). Finicky little sucker, isn't it, I thought.

Thinking there may perhaps be a hole that may still be there, I decided to drive for a while. Car felt perfectly fine with the left rear riding heavy, all the way into Richmond. I did bleed off some air when I got there but it still rides about 3 lbs heavier on the left rear than right rear. Ride and steering was just fine coming back to Northern Virginia today.

My questions:

(1) Does a full load front and rear throw off the TPMS operation?
(2) How much over and under can the rear tires be inflated without tire damage?

Thanks.......

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"He who dies with the most toys is, nonetheless, still dead." — Unknown

TPMS is only a warning system not a measurment tool.
Weights should have no effect.
Please see the FAQs for more.
There are a bunch of related threads to read but there are are lots of people who cannot grasp it's operation so be warned. Over/under inflation will not be required if you have a quality gauge (search ) and understand how to use it.

Now before one of you moderators go wonky on me, I did a search for TPMS and since there are literally dozens, I decided to pick the most recent dealing with the issue of weird TPMS readings. I've probably posted something about my issues sometime ago, but it goes like this: no reading; "did you change your wheels"; System learning; will not work while moving, etc. I got to the point where I essentially ignored the damn thing even though the dash lights were a nuisance.
So, I was at the dealer today for new tires, oil change and asked them to look at it. The tech comes to me and says there is nothing wrong but it's showing "interference"? "Do you park in a garage"? "Is there another car in the garage"? "Does it have TPMS"? Well, the answers were all in the affirmative. It sits next to my wife's MB CLS which has TPMS, although not quite as sophisticated as my CS... only warns of low pressure. So, the tech says, "that's the problem." Both systems read on exactly the same frequency and even when the cars are off, the system is searching for tire pressure info and it gets confused.
Has anyone else ever been told this? It was an epiphany for me if it's not hogwash. He says the FCC assigns the frequency for these things and there is simply no way to get around it. I did get nitrogen to help with some constancy of reading though. So, there you go. If this has been beaten to death before, my regrets...

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'07 CS, 6spd, Meteor Grey, stone grey, 19" Carrera Sport with meteor grey spokes/polished rim, headrest crests, bi-xenons, Bose, power seats, rain sensor, fire extinguisher, heated seats, dimming mirrors, FabSpeed Maxflo II catback
'06 CLS 500, white, beige
'04 Black Ranger Edge

The manual says "more than four wheel transmitters are detected", so I suppose if they are on identical frequencies it is possible. But mine is parked with another car with TPMS and there are no issues. (by the way system learning must be done while the car is moving not the way stated). But once the car is away from the competing frequency and put in learning mode it should come back to normal.

Also the manual talks about external interference by other radio sources (wireless headphones for example).

I NEVER thought of that. Personally, I've had the TPMS warn me of a flat tyre, but when I went to the tire pressure display screen, it read all pressures correctly! In the past I have fixed it by disconnecting the battery or just driving around for a while. I even had a tech tell me the sensor was faulty, to which I replied, "You just gotta restart the car." Sure enough, after a restart, it worked just fine. I wonder if this means that the presence of other Porsches will interfere with the TPMS.

After some period of driving, mine returns to normal but there are other wireless things about to, e.g., my home network, my iPhone. Ah! Technology! Ain't it wonderful.

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'07 CS, 6spd, Meteor Grey, stone grey, 19" Carrera Sport with meteor grey spokes/polished rim, headrest crests, bi-xenons, Bose, power seats, rain sensor, fire extinguisher, heated seats, dimming mirrors, FabSpeed Maxflo II catback
'06 CLS 500, white, beige
'04 Black Ranger Edge