Compass Mini-Trip Computer
Compass Mini-Trip Computer (CMTC) Switches and Display:
OPERATION
The Compass mini-trip computer (CMTC) system is located in the overhead console. CMTC consists of an electronic control module with a vacuum fuorescent display (VFD) and functioin switches. The CMTC consists of an electronic module that displays compass, trip computer and temperature features. Actuating the STEP switch will cause the CMTC to change mode of operation when the ignition is ON.
Examples:
- Compass/Temperature
- Trip odometer (ODO)
- Average miles per gallon (ECO)
- Instant miles per gallon (ECO)
- Distance to empty (DTE)
- Elapsed time (ET)
- Off
The information needed for the traveler functions is received over the CCD bus from the body control module.
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.
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 in this section.
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 in this section. 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. After demagnetizing, check compass calibration number, refer to Self Diagnostic Test. If greater than 15, demagnetize again until reading is less than 15. If compass still goes blank after demagnetizing then check internal diagnostics and demagnetize.
CIRCUIT OPERATION
The Compass Mini-Trip Computer (CMTC) is a display head used to provide the following information to the vehicle occupants:
- Compass and outside air temperature
- Current fuel economy
- Average fuel economy
- Distance to empty
- Trip odometer
- Elapsed time
The CMTC receives all information across the CCD Bus from various controllers and modules,, except for outside ambient air temperature.
Power for the CMTC is supplied by circuit A22. This circuit connects from the ignition switch to the CMTC and is HOT in the RUN position only
Circuit A22 connects from the ignition switch to a 10 Amp fuse located in cavity 10 of the junction block.
Power for the A22 circuit, and fuse 10, is supplied on circuit A2. This circuit is protected by a 40 Amp fuse located in cavity 2 of the Power Distribution Center.
Ground for the CMTC is provided on circuit Z2. This circuit terminates at the right cowl panel.
The outside air temperature sensor is located forward of the radiator, rear of the fascia. Circuits G31 and G32 are used to transmit the outside air temperature reading to the CMTC. These circuits are a twisted pair.
NOTE: If the compass mini-trip computer has been replaced, it may be necessary to reset the calibration.