I Just Don't Get the TPMS Sensors
 

So a few weeks ago I got new TPMS sensors from my tire shop since the old ones had died. The first problem is they measure 5 pounds less than actual reading(i've tried 3 different gauges). The stock ones measured 3 less than actual. The second problem and this is what I don't get. I believe the system is set up for 33/39 and to give an alarm if the pressures are -4 pounds. THe last few mornings it's been a little colder so my fronts were reading 29 pounds(34 pounds is the actual reading with a gauge) which set off the alarm. Around lunch after its warmed up the reading is back up to 30, so i reset the system but the alarm goes off still. I don't get it?

I'd return them and put the money towards OEM sensors, good luck

Interesting all of mine on multiple cars have been either dead on or +/- 1 pound. I never checked the porsche because they all show I am fine.

Mine read about 2 lbs low up front and about 4 lbs low in the rear. As long as the alarm isn't going off its fine. It's just a guide to confirm that all is well and that the tires are up to temp.

So why is it going off when when they are reading 30/36?

No idea, mine read 30/31 fronts depending on amb temp and 33/34 rear.
My actual pressures are 33/37 cold at 68 degrees.

Do you have the load set at full or partial? That will effect it.

Its set at partial.

How do you know your tire gauge is accurate? How has it been calibrated?

I have a digital gauge that I bought, I don't remember where. I've compared it to two different long acre fluid filled gauges and read within half a pound difference.

I've tried 3 different gauges and(one is a long acre) and they all are exactly the same.