I started my car this morning and got a message from the tire pressure system saying I had a flat. My right rear tire was reading 10 pounds less than other rear tire. Does this mean I have a leak or could it just be from letting it sit in the cold for the past 4 days.

Also, How accurate is the monitoring system. I tried the two different tire gauges I have and the porsche one was reading 5 pounds less than mine?

thanks

 

The TPMS is not spot on with a hand held gauge but that's fine as what it is telling you is that you have a probable nail in your tire. Generally, for those of us in the USA, the right rear is the most likely to pick up a small nail,--from near a curb or something. If you expect to see it reading 43 and it reads 33 that's what it is.

Take it into the shop or do what I did. I pull the wheel off, found the tiny nail, and plugged it. Some will tell you never to plug a tire but if you're unsure,--let a shop take a look at it.

That TPMS is doing exactly what it is supposed to do.

 

You will not lose 10 pounds in one tire just by sitting in the cold. You definitely have a leak of some kind, probably a nail as Dan says.
You might lose two or three pounds due to cold, but it would affect all tires the same, not just one tire.
The TPMS is doing its job.