Compass: Description and Operation
COMPASS/MINI-TRIP COMPUTERThe Compass/Mini-Trip Computer is located in the overhead console. The CMTC consists of a electronic control module with a vacuum fluorescent display (VFD) and function switches. It displays to the driver the direction the vehicle is traveling and the current outside temperature, as well as the following traveler navigational information:
- Average Fuel Economy (AVG ECO)
- Distance To Empty (DTE)
- Instantaneous Fuel Economy (ECO)
- Elapsed Time (ET)
- Trip Odometer (ODO)
Compass Mini-Trip Computer (CMTC) Switches and Display:
The CMTC module in the overhead console has three buttons used to select various functions. The CMTC selector buttons will not operate until the ignition is in the RUN position.
When the ignition switch is first turned to the RUN position, the CMTC display:
- Blanks momentarily
- All segments of the VFD will light for one second
- Blanks momentarily
- Returns to the last mode setting selected before the ignition was last switched OFF.
The information needed for the traveler functions is received over the CCD bus from the Body Control Module.
If the Compass/Mini-Trip Computer has been replaced, it may be necessary to reset the calibration.
SYSTEM OPERATION
Setting The Compass
The Compass/Mini-Trip Computer module is self-calibrated and requires no adjustment. The word CAL will be displayed to indicate that the compass is in the fast calibrating mode. CAL will turn off after the vehicle has gone in three complete circles without stopping, in an area free of magnetic disturbance.
If the module displays the temperature while the compass is blank or shows a false reading, the vehicle must be demagnetized. See the service procedure.
If the compass still goes blank after the vehicle is demagnetized, the compass/mini-trip module must be replaced.
Compass Magnetic Variance Zones:
Setting The Variance
Variance is the difference between magnetic north and geographic north. To determine the variance for the area you are in, refer to the following zone map provided. The number shown for your area is the variance number for your area.
1. Set the Compass/Mini-Trip Computer (CMTC) to Compass/Temperature mode.
2. Press and hold down the RESET button for 5 seconds. NOTE: If the button is held for 10 seconds instead of 5, the CMTC will set the variance to 8 and enter the fast calibration mode.
3. The VAR light will come on and the last variance setting will be displayed.
4. Press the STEP button to set the zone number.
5. Press the US/M button and resume normal operation,
NOTE: DO NOT ATTACH ANY MAGNETIC DEVICE SUCH AS A MAGNETIC CB ANTENNA TO THE VEHICLE. THIS CAN CAUSE THE COMPASS TO GIVE FALSE READINGS.
Compass Mini-Trip Computer Self Diagnostic Test
The Compass Mini-Trip Computer (CMTC) is capable of performing a diagnostic self check on many of its internal functions. CMTC diagnostics may be performed using a DRB lll scan tool and the proper Body Diagnostic Procedures or by the following procedure.
1. With the ignition switch in the OFF position, press both the US/M and STEP button.
2. Turn ignition switch to the ON position.
The CMTC will perform internal checks while lighting all segments of the vacuum florescent display. Upon completion of the internal check, the CMTC will display.
- PASS
- FAIL
- CCD
If any segment of the CMTC fails to light replace the module.
If FAIL is displayed, replace the module.
If CCD is displayed, check the CCD and Body Control Module (BCM) for proper operation, refer to the appropriate diagnostic test procedures. If the CCD and the BCM are OK, replace the CMTC module.
For additional diagnostic information on the CMTC and for identifying CMTC problems, refer to the proper Body Diagnostic Procedures.
Compass
The CMTC is self calibrating and usually requires no adjustment. The compass will continuously perform a slow calibration to compensate for small magnetic variations common to any automobile. Uncommon magnetic shifts may be caused by items such as magnetic base antennas, which can permanently alter the magnetic field of the vehicle roof panel. If excessive magnetic field continues for 5 minutes, the compass heading will go blank and only the CAL symbol will illuminate. When this occurs, the vehicle roof panel may require demagnetizing. Refer to the demagnetizing procedure.
Moderate magnetic shifts may, on very rare occasions, cause the compass heading to display only one or two of the eight possible headings. Although the compass will eventually compensate for this shift, it could take several ignition cycles. The compensation process can be expedited by manually activating the fast calibration routine. Refer to the fast calibrating procedure. This procedure may be performed anytime that the compass appears to be inaccurate.
If the calibration data stored in the body control module is not received, the compass will read only NE North-East. The CMTC is self calibrating and requires no adjusting. The word CAL is displayed to show that the compass is in calibration mode. CAL will turn off after the vehicle has gone through three complete circles without stopping, in an area free of magnetic disturbance. If module displays temperature while the compass is blank, turn off ignition and run self diagnostics then demagnetize the vehicle. If problem persists, then demagnetize vehicle.