I have a 07. My lights was on. They ened up replacing a sensor in the rim. Turns out the rear passengers casued the issue. Check with a dealer. Its a call away.

 

I have the very same problem on a 2001 LS 3.4L.
I bought the car used in 2004 with 28,000 miles. After about 6 months, I went to start it one day, and the security light came on in the dash display and the car wouldn't turn over. The BCM was replaced (which controls the tire pressure monitor also). After it was replaced, the tire pressure warning can't be accessed through the menu on the radio. The option just isn't there.

Unfortunately, I haven't ever brought it back to a dealer to have the BCM checked out again. The warning light is the only issue, and any garage can shut it off (i'm pretty sure you can do the gas pedal trick to clear all the codes to clear the tire pressure code), so I don't want to take it in and pay for diagnostics since it's the only issue.

Let me know if you find out what's wrong, I'd like to know as well since I have the exact same problem.

 

I'm still of the suggestion to bring the car into the dealership. Do it for an oil change or something and they normally do it for free.