So do these things give you a psi readout on the display or is it just a warning system that turns on once the tires are low or to high?

 

it gives you a warning when the air pressure gets too low....about 25psi or so.....my wife picked up a nail and it gave a warning before it was low enough for me to notice.....worked well...

 

I've a 2006 FWD Touring and I've had the readout light on since I bought it last week.
33psi seemed an aweful low tire pressure since the tires that are on it (235x55x19) have a 44max rating.
At 33psi the car steers like I'm driving a tank and gas mileage sucks......13mpg.
Since putting in 38 the drive has improved markedly and mpg is at 19.3. I've driven over 1000 miles since gettting the car and it should have retaught itself by now. I don't have a magnet and theres no calibration menu that I can find......HELP.

 

Well the tire sensor is fixed. They had to magnet and reprogram the tire. From the factory it was messed up.
If you buy one have them do it before you drive off the lot.