Compass: Description and Operation
MODULE-COMPASS TEMPERATUREDESCRIPTION
The compass mini-trip computer (2) is located in the overhead console (1) 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 (TRIP 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.
- 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 level of the fuel in the tank and a weighted average of long term and recent Average Fuel Economy.
- 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 ambient temperature sensor is hard wired to the HVAC control head (4.7L equipped vehicles are hard wired to the Next Generation Controller). 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 as described. If these tests prove inconclusive, the use of a DRB scan tool and the proper Diagnostic Procedures manual are recommended for further testing of the compass mini-trip computer module and the J1850 data bus.
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.
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 one or two complete circles, on level ground, in not less than 16 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 may be required to restore proper compass operation.
TEMPERATURE
The temperature 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 temperature 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 temperature unit memory. When the ignition switch is turned to the On position again, the temperature will display the memory temperature if the engine OFF time is less than 90 minutes. If the engine OFF time is more than 90 minutes, the temperature will display the actual temperature sensed by the ambient temperature sensor. The temperature display update interval varies with the vehicle speed.
The temperature 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 (4.7L equipped vehicles are hard wired to the Next Generation Controller), 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 min and max temperatures of -40° C (-40° F) and 54° C (130° F).
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 the RESET push button is depressed 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. All three of these functions can be reset at once by pressing the RESET button twice within 3 seconds while any one of the three functions is selected. see the owner's manual in the vehicle glove box.