I just picked up a new (to me) 2007
Boxster Base
5 Speed w/18 inch factory wheels. Somehow the TPC/TPMS thinks the tires should have 47lbs of air in them. Anything less and it gives me a pressure or flat tire warning. I've fiddled with the on board computer but cannot find a way to change the "normal" pressures. How do I reset the TPC system so that it knows that the correct pressures are 30 front and 37 rear?
UPDATE: I went to check the reading on the dashboard display and it looks like the TPC/TPMS is reading pressures that are well below what the actual pressures in the tires are. For example, it shows 30lbs in a rear tire that I know has 37lbs in it. Any thoughts on what I can do?
Thanks.
2007
Boxster Base
MT
1996 993 C2 (gone but not forgotten)
Either your reference gauge is wrong, or the TPMS sensor is wrong... that's too big of a difference to be "in the noise".
Proper is 30psi rear on my 2010, so even 37 surprises me, but go with whatever your label says. I agree the readings shouldn't have that much difference.
If the reading from your reference is truly correct, then I'd suspect the TPMS may be wrong/dying/etc? A tire shop should be able to check them with specialized tools to ensure the batteries are fine, and they are the correct ones for the car... maybe there's something funny with the existing ones?
Beyond that, you can try setting a different size via the on board computer, and then set it back, and see if that resets it somehow?
Thanks for the reply. I used 2 different reference gauges (including one at the tire store) to make sure the pressures in the tires were correct and to establish that the on board tpc/tpms was wrong. I'll see if the tire shop can test the on board tpms-s to see if that is where the problem is.
If I replcace the tpms-s in the wheels can the car's on board tpc be programmed to recognize them?
I have a
2008 Cayman S
and the displayed pressures on my car are typically 2-3 psi less than measured with a gauge (both cold and hot). The TPM screen typically shows 0, +1, or -1 if I look at it when doing this comparison so for me the displayed pressure is a little low but the absolute pressure difference seems to be pretty accurate.
The sensors have to be compatible with the TPMS electronics, not the other way around. You want sensors that are known to work with your car. I would trust Tirerack with this - I've used them for sensors several times and they always worked after doing a TPMS reset (change season/tire, then change back.. drive.)
And as far as trusting the shops gauge? Just because they're using it doesn't mean it's accurate. If anything the amount of use and banging around a shop gauge might see vs yours that sits in the drawer 364 days of the year might have a significant effect on the shop gauge accuracy.
Funny - I have a digital gauge attached to a fill-trigger mechanism, bought from Harbor Freight (small money) - and it agrees with the TPMS dead-nuts on. Prior to that, I had a HF dial filler, same thing but an analog gauge - and it was also dead-nuts on compared to the TPMS readouts.
Agreed, my gauges are on-target with the dash reading within +/-1psi (the external one reads in tenths, and the dash only does x. after all).
I'm thinking maybe you have bad sensors (ie, they work, but aren't sending the "right" signal to the car... or they are damaged, etc). Or maybe there's a way to change the programming curve in the ECU to interpret the PSI incorrectly? In the end, it's getting a number, and needs to convert that to PSI... that math could "potentially" be altered via
PIWIS
or something? Never heard of it, but as someone who works on sensors and systems on a daily basis, it's not that hard to do if you can get access.)
Again, try changing the tire size/spec on the onboard, and see if the values change... and when you restore them to your actual tire size, see if they work properly (ie, erases the manual changes, if they happened at all).
