Trip Computer: Description and Operation

COMPASS/MINI-TRIP COMPUTER
The 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).

Pushing the STEP button when the ignition is ON will cause the CMTC to change mode of operation.

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

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 Mini-Trip Computer (CMTC)

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.

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.