i have a 2000 gmc sierra 1500, the temp gauge on the rearview mirror says OC, the compass works fine, any ideas??

I would check the to make sure the wiring is still connected. You may have a bad wire or possibly a bad sensor.

I believe "OC" stands for open circuit. Whatever it stands for, sdowning1967 is right. Check the wiring from the mirror to the temp sensor in front of the radiator. Compass wiring is all self contained in the mirror.

Did you ever find the trouble with the temp on your mirror I am having the same problem ?

wow, what an archaeologist find!

Almost 3 years old...21 dog yeas!!!

Did you do any recent work on or around the radiator or lower grille area, I think that is where the sensor is closer to the road, also try unplugging the plug at the back of the mirror and reseating it, I had errors too after I had spliced into the auto dim circuit to power my Escalade auto dim mirror I installed on the drivers side.