Auto dimming mirrors will stop working if the sensors are turned off. Make sure the sensors are getting power and reset them if possible to see if they start working again. \
Sensors may also be grimy or dirty due to simple buildup over time. Wipe off the sensors with a clean, damp cloth. \
Use a soft cloth and work gently so as not to scratch or damage the sensors, which are sensitive. Also carefully wipe around the sensors to make sure there is no dust, hair, or other debris possibly blocking the sensors and preventing them from working properly. \