Compass: Description and Operation

Compass/Temperature Mini-trip Computer

Compass/Temperature Mini-Trip Computer:

CTMC Module:

The Compass/Temperature Mini-Trip Computer (CMTC) system is located on the right hand side of the instrument panel cluster. The CMTC is an electronic control module with a vacuum fluorescent display and two function buttons. The CMTC is capable of displaying compass, temperature, and trip computer information. Actuation of the STEP button will cause the CMTC to change mode of operation and actuation of the US/M button will toggle between English and Metric unit of measurement. A reset of the trip computer information is accomplished by actuating the Step and US/M buttons simultaneously.

The CMTC is active only when the ignition switch is in the ON position. When the ignition switch is turned ON, the CMTC will turn on all of the segments in the display for one second then return to the last function screen that was displayed prior to the ignition being turned OFF. The functions that are available via activation of the STEP switch are as follow:
- Compass and Ambient Temperature
- Average Trip Fuel Economy (AVG ECO)
- Estimated Range (RANGE)
- Present Fuel Economy (ECO)
- Trip Odometer (ODO)
- Elapsed Ignition On Time (ET)
- Blank Screen

Compass
The CMTC is an auto-calibrating compass and requires no activation of any switches to trigger a forced calibration. The compass is initially setup to be calibrated for earth fields of approximately 180 milligauss. However, due to the variation in the magnetic earth field across the country and the variation of the magnetic structure from vehicle to vehicle the compass may need to be calibrated. Refer to Compass Calibration Service Procedures.

Ambient Temperature
The temperature is displayed in whole degrees Celsius or Fahrenheit. Temperatures greater than or equal to zero are displayed unsigned and temperatures below zero are displayed signed (-). If the temperature is more than 55° C (131° F) or the temperature sending line is shorted to ground, the compass and ambient temperature screen will display SC. If the temperature is less than -40° C (-40° F) or the temperature sending line is an open circuit, the compass and ambient temperature screen will display "OC". If the CMTC is not receiving the temperature information over the CCD Bus, then the compass and ambient temperature screen will display "CCd". Refer to the proper Body Diagnostic Procedures.

Mini Trip Computer Messages
The Mini Trip Computer data is obtained from information put on the CCD bus from the Powertrain Control Module (PCM) and the Body Control Module (BCM). The CMTC will not display information for any of the screens for which it did not receive the proper data over the CCD bus for that particular screen. In this case the message "CCD" will be displayed. If some of the screens appear to be functioning properly but some of the screens display "CCd" then check either the Powertrain Control Module or the Body Control Module for proper CCD bus communications. If the "CCd" message still persists, refer to the Mini Trip Computer Self Diagnostic Test.