I have a similar problem, but only in cold temperatures.OUr 2011 Odyssey has a dashboard thermometer that seems to be off by as much as 8-9 degrees. Our dealer spent several hours calibrating it to the local weather station, but it still will show 91 degrees when it is 100 or more.
OUr 2003 Toyota Matrix had one that was quick and accurate so I know they are available.
Anyone familiar with this issue and possible solutions?
here's my thread:
outside-temperature-sensor-not-accurate