We are talking about 2 different things. The low tire pressure light is not the problem. I am talking about the tire pressure guage that is located where the navagitation system is. This usually shows the exact tire pressure for each tire but now shows only---.
Oh. I'm sorry. I misunderstood.
Unfortunately, this must be done with the use of a scan-tool ("Consult-II"). If this display is showing "---" then more than likely there is a problem in the system, and you will need the use of a scan tool to figure out where the problem lies. Here is the procedure for the reset, you'll notice it requires a "Consult-II" (scan-tool):
Select "AIR PRESSURE MONITOR" on "SELECT WORK ITEM" screen.