Inside Rearview Mirror with Compass System Operation
WARNING: This page is about a different car, the 2008 Cadillac CTS. However, it is still accessible from the selected car via links, so may be relevant.
The inside rearview mirror consist of 2 magnetic field sensors that control compass displays. Each magnetic sensor is responsible for 2 headings. There is a north/south sensor and an east/west sensor. The inside rearview mirror supplies each sensor with a signal and low reference voltage. As the vehicle travels with or against the earths magnetic pull there will be a change in voltage on one or both magnetic sensors. As the voltage changes at the sensors the inside rearview mirror will change the heading of the compass display.