Dodge Ram Truck 1500-2500-3500. Manual — part 461

SELF- DIAGNOSTIC TEST

A self-diagnostic test is used to determine that the EOM is operating properly electrically. Initiate the self-diagnostic
test as follows:

NOTE: The compass mini-trip computer self - test can also be performed using a scan tool. Refer to Auto
Self Test under the System Tests.

1. With the ignition switch in the Off position, simultaneously depress and hold the STEP and RESET buttons while

rotating the ignition switch to the Run/On position.

2. Continue to hold both buttons depressed until the EOM enters the display segment test. In this test, all of the

Vacuum Fluorescent Display (VFD) segments are lighted while the EOM performs the following checks:

•

Non-Volatile Memory Status (NVM)

•

RAM Status

•

ROM Status

•

ASIC Communication Test Status

•

Compass Test Status

•

DC Status

•

PCI data bus Communications Test

NOTE: If module is equipped with the Universal Transmitter, the module also checks “Universal Transmitter
Communication Test Status”

3. Following completion of these tests, the compass mini-trip computer will display one of two messages: “FAIL” or

“PASS.” Press RESET or STEP to exit and enter normal mode. Respond to these test results as follows:

•

If no test result message is displayed, but compass mini-trip computer operation is still improper, the use of a
scan tool and the proper Diagnostic Procedures Information are required for further diagnosis.

•

If the “FAIL” message is displayed, the EOM is inoperative and must be replaced.

•

If the “PASS” message is displayed, the EOM is OK, no faults are present.

•

If any VFD segment does not light during the display segment test, the EOM is inoperative and must be
replaced.

4. If the first seven tests pass, the compass mini-trip computer shall verify that all the required PCI bus messages

are present on the PCI bus. If all required messages are present on the PCI bus, or if the ignition switch is
turned to the Off position, the EOM will automatically return to normal operation. The required PCI bus messages
are:

•

Dimming message

•

Fuel Used message

•

Distance Pulses message

•

Percentage Fuel Tank Full message

•

Fuel Type message

•

VIN (Vehicle Identification Number)

•

Vehicle Speed message

•

Last Engine Off Duration message

•

Ambient Air Temperature message

NOTE: The Fuel Used message shall be ignored if the engine type is Diesel or Compressed Natural Gas.

NOTE: Pressing the STEP or RESET switches during any portion of the testing procedure will cause the
compass mini-trip computer to exit diagnostics and return to compass/temperature mode.

NOTE: If the compass functions, but accuracy is suspect, it may be necessary to perform a variation adjust-
ment. This procedure allows the compass unit to accommodate variations in the earth’s magnetic field
strength, based on geographic location.

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NOTE: If the compass reading has blanked out, and only “CAL” appears in the display, demagnetizing may
be necessary to remove excessive residual magnetic fields from the vehicle.

STANDARD PROCEDURE

READING/COURTESY LAMP REPLACEMENT

1. Disconnect and isolate the battery negative cable.

2. Remove the reading/courtesy lamp lens. Using a trim stick, gently pry the forward edge of the reading/courtesy

lamp lens outward.

3. Remove the reading/courtesy lamp socket from the overhead console. Rotate the reading/courtesy lamp socket

one quarter turn counter clockwise.

4. Remove the lamp and socket assembly.

5. Reverse the above procedure to install.

MODULE LENS REPLACEMENT

1. Remove the overhead console, (Refer to 8 - ELECTRICAL/OVERHEAD CONSOLE - REMOVAL).

2. Remove the electronic overhead module from the overhead console, (Refer to 8 - ELECTRICAL/OVERHEAD

CONSOLE/COMPASS/MINI-TRIP COMPUTER - REMOVAL).

3. Unsnap the lens from the module and replace lens as necessary.

MODULE LAMP REPLACEMENT

1. Remove the overhead console (Refer to 8 - ELEC-

TRICAL/OVERHEAD CONSOLE - REMOVAL).

2. Using a flat blade screwdriver twist out socket/lamp

(3).

3. Replace lamp(s) as necessary.

REMOVAL

OVERHEAD CONSOLE REMOVAL

1. Disconnect and isolate the battery negative cable.

2. Remove the overhead console retaining screws, located in the sunglass storage bin.

3. Using your fingertips, grasp the sides of the overhead console and pull straight down evenly to disengage the

two snap clips at the front of the unit.

4. Lower the overhead console far enough to access the wire harness connectors.

5. Disconnect the Electronic Overhead Module and the reading/courtesy lamps electrical connectors.

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6. Remove the overhead console from the vehicle.

INSTALLATION

1. Position the overhead console in the vehicle.

2. Connect the Electronic Overhead Module and the reading/courtesy lamps electrical connectors.

3. Grasp the sides of the overhead console and push straight up evenly to engage the two snap clips at the rear

of the unit.

4. Install the overhead console retaining screws, located in the sunglass storage bin. Torque the screws to 1.2 N·m

(10 in. lbs.).

5. Connect the battery negative cable.

MODULE-COMPASS TEMPERATURE

DESCRIPTION

The compass mini-trip computer is located in the over-
head console (7) on models equipped with this option.
The compass mini-trip computer includes a Vacuum-
Fluorescent Display (VFD) (6), an Electronic Overhead
Module (EOM) and push button function switches (1,
2, 4 and 5).

The compass mini-trip computer module contains a
central processing unit and interfaces with other elec-
tronic modules in the vehicle on the Programmable
Communications Interface (PCI) data bus. The PCI
data bus allows the sharing of sensor information. This
helps to reduce wire harness complexity, reduce inter-
nal 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 fea-
tures that the compass mini-trip computer 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 Front Control Module (FCM). Data input for all other compass
mini-trip computer functions, including VFD dimming level, is received through PCI data bus messages. The com-
pass 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. (Refer to 8 - ELECTRICAL/OVERHEAD
CONSOLE - DIAGNOSIS AND TESTING) for the appropriate test procedure. If these tests prove inconclusive, the
use of a scan tool and the proper Diagnostic Procedures Information are recommended for further testing of the
EOM and the PCI data bus.

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The EOM cannot be repaired, and is available for service only as a unit. This unit includes the push button
switches, the Universal Garage Door Transmitter and the plastic module and display lens. If any of these compo-
nents is inoperative or damaged, the complete EOM 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, (Refer to 8 - ELECTRI-
CAL/OVERHEAD CONSOLE/COMPASS/MINI-TRIP COMPUTER - STANDARD PROCEDURE - COMPASS
DEMAGNETIZING) 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 temper-
ature 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 min-
utes, the temperature will display the actual temperature sensed by the ambient temperature sensor. The temper-
ature display update interval varies with the vehicle speed.

The temperature function is supported by an ambient temperature sensor. The sensor is mounted outside the pas-
senger compartment near the front and center of the vehicle, and is hard wired to the FCM, which sends temper-
ature over the PCI data bus circuit. The ambient temperature sensor is available as a separate service item, (Refer
to 8 - ELECTRICAL/OVERHEAD CONSOLE/AMBIENT TEMP SENSOR - DESCRIPTION).

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 igni-
tion switch is turned to the On position, all of the seg-
ments in the compass mini-trip computer Vacuum-
Fluorescent Display (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 (4) will cause the compass-mini-trip computer
to change its mode of operation. Momentarily depress-
ing and releasing the U.S./Metric push button (1) will
cause the unit to toggle between U.S. and Metric
measurements. Momentarily depressing and releasing
the C/T (compass/temperature) push button (5) will
cause the compass mini-trip computer to return to the
compass/temperature display mode from any other
mode.

This compass mini-trip computer features several
functions that can be reset. If the RESET push button

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