Compass: Description and Operation

COMPASS/MINI-TRIP COMPUTER (CMTC)
The Compass/Mini-Trip Computer (CMTC) system is located in the overhead console. The CMTC consists of an electronic control module with a vacuum fluorescent display (VFD) and function switches. The CMTC 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), and trip odometer (ODO). The information needed for the traveler functions is received over the CCD bus from the Body Control Module.

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 will:
- Blank momentarily
- Light all segments of the VFD for one second
- Blank momentarily
- Return to the last mode setting selected before the ignition was last switched OFF

Actuating the STEP switch will cause the CMTC to change mode of operation when ignition is ON. Example:
- Compass/Temperature
- Trip odometer (ODO)
- Average miles per gallon (AVG ECO)
- Instant miles per gallon (ECO)
- Distance to empty (DTE)
- Elapsed time (ET)
- Off

THERMOMETER AND COMPASS
Thermometer
Engine temperature can increase the displayed temperature. The CMTC is designed to dampen temperature readings when the vehicle is moving at a rate slower than 18 miles per hour.

The outside temperature is measured from a sensor mounted in the front of the vehicle. If the temperature is more than 55 °C (131 °F) or the temperature sending line is shorted to ground, the temperature display should read SC. If the temperature is less than -40 °C (-40 °F), or the sending line is an open circuit, the display should read OC.

The CMTC will not allow the temperature reading to increase when the vehicle is not moving.

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 compensator 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. All problem persists, then demagnetize vehicle.