Principles of Operation

Electronic Compass

Principles of Operation

NOTE: The Smart Junction Box (SJB) is also known as the Generic Electronic Module (GEM).

NOTE: This procedure is only applicable to vehicles without navigation. For vehicles with navigation, refer to Information and Entertainment Systems Testing and Inspection.

The compass display (located in the Front Display Interface Module (FDIM)) receives battery voltage from the SJB. The compass module (integral to the auto-dimming interior mirror) provides hardwired vehicle directional inputs to the Instrument Panel Cluster (IPC), which sends the compass information to the FDIM over the Medium Speed Controller Area Network (MS-CAN). The compass is capable of self-calibrating. This decreases the need to manually set the compass. If the compass is displaying a heading (and not displaying the C or CAL indicator), the compass is in auto-calibration mode. In this mode, the compass automatically calibrates for changes in vehicle magnetics over the life of the vehicle. This auto-calibration mode makes sure the compass heading is always accurate. If the compass displays the C or CAL indicator for an extended period of time (longer than 5 seconds), this indicates the compass has been placed in the manual calibration mode and therefore, requires manual calibration. Refer to Compass Calibration Compass Calibration.