Principles of Operation

Electronic Compass

Principles of Operation

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

The compass display is located in the Front Display Interface Module (FDIM). The compass module (integral to the interior rear view mirror) provides vehicle directional inputs to the Instrument Cluster (IC), which sends the compass information to the FDIM over the Medium Speed Controller Area Network (MS-CAN). The FDIM displays the compass direction according to the information that has been provided by the compass module to the IC.

The compass signal is sent through hardwired circuits from the compass module in the interior rear view mirror to the IC, which sends it over the MS-CAN to the FDIM.

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 that 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. The compass may temporarily display the C or CAL indicator if the vehicle characteristics have changed (car wash, collision or other factors), with the C or CAL indicator turning off after the vehicle characteristics have returned to normal. If the C or CAL indicator does not turn off after the vehicle characteristics have returned to normal, manual calibration is necessary. Refer to Compass Calibration Compass Calibration. After calibration, the normal compass display returns to the FDIM.

Compass calibration/zone adjustment is controlled by the 7 and 9 buttons on the Front Controls Interface Module (FCIM), which provides access to the calibration and zone adjustment procedures.

Excessive magnetism in or near the vehicle may cause the compass to illuminate all segments on the display. In order to distinguish between vehicle and surrounding magnetics, drive the vehicle to an area that is free from large metal objects, such as bridges, steel buildings, etc. Cycling the key on and off resets the compass.