Trip Computer: Description and Operation

COMPASS/MINI-TRIP COMPUTER
The Compass/Mini-Trip Computer is located in the overhead console on models equipped with this option. The compass mini-trip computer units include the electronic control module, a Vacuum-Fluorescent Display (VFD), a compass sensor unit and two push button function switches.

The Compass/Mini-Trip Computer module contains a central processing unit and interfaces with other electronic modules in the vehicle on the Programmable Communication Interface (J1850) data bus network. The J1850 data bus network allows the sharing of sensor information. This helps to reduce wire harness complexity, reduce internal controller hardware, and reduce component sensor current loads. At the same time, this system provides increased reliability, enhanced diagnostics, and allows the addition of many new feature capabilities.

The Compass/Mini-Trip Computer provides several electronic functions and features. Some of the functions and features that the compass mini-trip computer module supports and/or controls, include the following display options:
- Compass and Temperature - provides the outside temperature and one of eight compass readings to indicate the direction the vehicle is facing.
- Trip Odometer (ODO) - shows the distance travelled since the last trip computer reset.
- Average Fuel Economy (AVG ECO) - shows the average fuel economy since the last trip computer reset.
- Instant Fuel Economy (ECO) - shows the present fuel economy based upon the current vehicle distance and fuel used information.
- Distance To Empty (DTE) - shows the estimated distance that can be travelled with the fuel remaining in the fuel tank. This estimated distance is computed using the average miles-per-gallon from the last 30 gallons of fuel used.
- Elapsed Time (ET) - shows the accumulated ignition-on time since the last trip computer reset.
- Blank Screen - the compass mini-trip VFD is turned OFF.

The Compass/Mini-Trip Computer uses two push buttons to toggle the display and reset various functions. These push buttons include:
- Step Button - Press this button to cycle through all the mini-trip computer displays.

- US/M Button - Press this button to convert all vehicle displays from US to Metric to US.

The Compass/Mini-Trip Computer module cannot be repaired, and is available for service only as a unit. This unit includes the push button switches and the plastic module and display lens. If any of these components is faulty or damaged, the complete compass mini-trip computer module must be replaced.

To Reset the Display
Press the Step and US/M buttons simultaneously for at least two seconds and all resettable conditions will be reset. This will occur only if a resettable function (AVG ECO, ECO, ET) is currently being displayed.

Ambient Temperature Sensor
The ambient temperature sensor is hard wired to the HVAC control head. Data input for all other Compass/Mini-Trip Computer functions, including VFD dimming level, is received through J1850 data bus messages. The Compass/Mini-Trip Computer uses its internal programming and all of these inputs to calculate and display the requested data. If the data displayed is incorrect, perform the self-diagnostic tests. If these tests prove inconclusive, the use of a DRB scan tool and the proper Diagnostic Procedures are recommended for further testing of the compass mini-trip computer module and the J1850 data bus.

COMPASS
While in the compass/temperature mode, the compass will display the direction in which the vehicle is pointed using the eight major compass headings (Examples: north is N, northeast is NE). The self-calibrating compass unit requires no adjusting in normal use. The only calibration that may prove necessary is to drive the vehicle in three complete circles, on level ground, in not less than 48 seconds. This will reorient the compass unit to its vehicle.

The compass unit also will compensate for magnetism the body of the vehicle may acquire during normal use. However, avoid placing anything magnetic directly on the roof of the vehicle. Magnetic mounts for an antenna, a repair order hat, or a funeral procession flag can exceed the compensating ability of the compass unit if placed on the roof panel. Magnetic bit drivers used on the fasteners that hold the overhead console assembly to the roof header can also affect compass operation. If the vehicle roof should become magnetized, the demagnetizing and calibration procedures found may be required to restore proper compass operation.

The Compass/Mini-Trip Computer only operates with the ignition switch in the ON position. When the ignition switch is turned to the ON position, all of the segments in the Compass/Mini-Trip Computer VFD will be turned OFF for one second, then the display will return to the last function being displayed before the ignition was turned to the OFF position. With the ignition switch in the ON position, momentarily depressing and releasing the Step push button switch will cause the Compass/Mini-Trip Computer to change its mode of operation, and momentarily depressing and releasing the U.S./Metric push button will cause the unit to toggle between U.S. and Metric measurements. This Compass/Mini-Trip Computer features several functions that can be reset. If both the Step and U.S/Metric push buttons are depressed at the same time for more than one second with the ignition switch in the ON position, the trip computer information that can be reset is reset. However, the reset will only occur if the function currently displayed is a function that can be reset. The functions that can be reset are: TRIP ODO, AVG ECO, and ET.

For more information on the features and control functions of the Compass/Mini-Trip Computer, see the owner's manual in the vehicle glove box.

Automatic Compass Calibration
This compass is self calibrating which eliminates the need to manually set the compass. When the vehicle is new, the compass may appear erratic and the CAL symbol will be displayed. After completing three 360' turns in an area free from large metal or metallic objects, the CAL symbol will turn OFF and the compass will function normally.

Compass Variance
Compass Variance is the difference between Magnetic North and Geographic North. In some areas of the country, the difference between Magnetic and Geographic North is great enough to cause the compass to give false readings. If this occurs, the compass variance must be set.

To Set The Variance
Turn the ignition ON and set display to Comp./Temp. while pressing the US/M button, press the STEP button for approximately five seconds. The "VAR" symbol will light and the last variance zone number will be displayed. Press the US/Metric Button to select the proper variance zone as shown on the map. Press the Step button to set the new variance zone and resume normal operation.

THERMOMETER
The thermometer displays the outside ambient temperature in whole degrees. The temperature display can be changed from Fahrenheit to Celsius using the U.S./Metric push button. The displayed temperature is not an instant reading of conditions, but an average temperature. It may take the thermometer display several minutes to respond to a major temperature change, such as driving out of a heated garage into winter temperatures.

When the ignition switch is turned to the OFF position, the last displayed temperature reading stays in the thermometer unit memory. When the ignition switch is turned to the ON position again, the thermometer will display the memory temperature if the engine coolant temperature is above about 52 °C (125 °F). If the engine coolant temperature is below about 52 °C (125 °F), the thermometer will display the actual temperature sensed by the ambient temperature sensor. The thermometer temperature display update interval varies with the vehicle speed.

The thermometer function is supported by an ambient temperature sensor. The sensor is mounted outside the passenger compartment near the front and center of the vehicle, and is hard wired to the HVAC control head which sends temperature on J1850 data bus circuit. The ambient temperature sensor is available as a separate service item.

NOTE: The compass mini-trip computer will display "OC" for temperatures below -40 °C and "SC" for temperatures above 55 °C.