. So I have a question, my front ire says 13'C and my rear 23'C , same garage floor and it shows 41 PSI front and 46PSI rear, are these the last readings?
Yep, I'm getting the same thing in the mornings. Once you start rolling, after a couple hundred meters you should see current values.
The last snapshot memory can be confusing, but it makes sense, technically speaking. If the central unit were to send a "I woke up, please send current readings" to the wheel sensors, the wheel sensors would need to be capable of receiving radio signals. It's probably cheaper to make them so they just broadcast every minute after they've sensed movement, transmit-only and non-interactive. Also makes them smaller and the battery lasts longer, since it doesn't need to be on alert for incoming signals.
The central unit probably doesn't discern between being put to sleep for a minute (filling up at a gas station, the last snapshot is probably still accurate) or an entire night (tires have cooled down, readings inaccurate), so they decided it would always shows the last snapshot if they have one. Simple and works fine in most cases. In order for it to know the difference and show "--" in the morning, they'd need to put a clock in there and a bunch of extra code. More expensive, more complicated, for little gain.
It does know when it's been turned off completely, because its snapshot memory is wiped, so then it shows "--".
At least that's how I think it works, as a software engineer