mirror temp not working

Hi. The mirror on my 1998 tahoe stopped displaying temp in fahrenheit. It still works in celsius and direction. How would I fix this?
thanks
tom

Do a reset... Press & hold the TEMP. button for 3 seconds until the display blinks F and C, press & release the TEMP switch to change between the F and C reading. Hope this helps, if you have your owners booklet, go to page 2-47.