Diagnosis And Testing; Thermometer; Module - Jeep 1996 Grand Cherokee Service Manual

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DIAGNOSIS AND TESTING

TRIP COMPUTER/COMPASS/DISPLAY MODULE
If the problem with the trip computer/compass/dis-
play module is an inaccurate or scrambled display,
use the Self-Diagnostics procedures. If the problem is
a no-display condition, use the following procedures.
For circuit descriptions and diagrams, refer to 8W-49
- Overhead Console in Group 8W - Wiring Diagrams.
(1) Check the fuses in the junction block. If OK, go
to Step 2. If not OK, replace the faulty fuse(s).
(2) Remove the overhead console as described in
this group. Check for continuity between the ground
circuit cavity of the overhead console connector and a
good ground. There should be continuity. If OK, go to
Step 3. If not OK, repair the circuit to ground as
required.
(3) Check for battery voltage at the fused B(+) cir-
cuit cavity of the overhead console connector. If OK,
go to Step 4. If not OK, repair the open circuit to the
junction block as required.
(4) Turn the ignition switch to the On position.
Check for battery voltage at the fused ignition switch
output cavity of the overhead console connector. If
OK, go to Step 5. If not OK, repair the open circuit to
the junction block as required.
(5) Check for continuity between the courtesy lamp
relay output circuit cavities of the overhead console
connector and the junction block receptacle for the
courtesy lamp relay. There should be continuity. If
OK, proceed to the self-diagnostic tests in this group
for further diagnosis of the module and the CCD data
bus. If not OK, repair the open circuit to the courtesy
lamp relay as required.
SELF-DIAGNOSTICS
A self-diagnostic test is used to determine that the
trip computer, compass, and all of the display module
segments are operating properly electrically. Initiate
the self-diagnostic test as follows:
(1) With the ignition switch in the Off position,
simultaneously press and hold the Step button and
the U.S./Metric button.
(2) Turn the ignition switch to the On position.
(3) Continue to hold both buttons, until the display
module performs a display segment test. In this test,
all of the vacuum fluorescent display segments are
lighted. This test will:
a. Verify that all display segments are functional
b. Check the internal circuitry of the module
c. Check that all of the CCD data bus messages
needed are being received.
(4) In the display segment test (a), if any segment
should fail to light the unit is faulty and must be
replaced. If test (b) is failed, the module will display
"FAIL". If "FAIL" is displayed, the unit is faulty and
OVERHEAD CONSOLE SYSTEMS
must be replaced. If test (c) is failed, the module will
display "CCD". If "CCD" is displayed, the use of a
DRB scan tool and the proper Body Diagnostic Pro-
cedures Manual are required for further diagnosis. If
all tests are passed, the module will automatically
return to normal operation.
(5) Momentarily depress and release either button
one time to exit the self-diagnostic mode and return
the trip computer, compass, and display module to
normal operation.
NOTE: If the compass functions, but accuracy is
suspect, it may be necessary to perform a variation
adjustment. This procedure allows the compass
unit to accommodate variations in the earth's mag-
netic field strength, based on geographic location.
See the Compass Variation Adjustment procedures,
in this group.
NOTE: If the compass reading has blanked out, and
only "CAL" appears in the display module, demag-
netizing may be necessary to remove excessive
residual magnetic fields from the vehicle. See the
Compass Demagnetizing procedure, in this group.

THERMOMETER

The thermometer function is supported by a tem-
perature sensor, a wiring circuit, the Body Control
Module (BCM), the CCD data bus, and a portion of
the overhead console trip/computer/compass/display
module display. The sensor is mounted outside the
passenger compartment near the front and center of
the vehicle.
If any portion of the temperature sensor circuit
fails, the thermometer display will self-diagnose the
circuit. An "SC" (short circuit) will appear on the dis-
play module in place of the temperature when the
sensor is exposed to temperatures above 55°C
(131°F), or if the sensor circuit is shorted. An "OC"
(open circuit) will appear in place of the temperature
when the sensor is exposed to temperatures below
-40°C (-40°F), or if the sensor circuit is open.
The temperature sensor circuit can also be diag-
nosed using the following Sensor Test, and Sensor
Circuit Test. If the temperature sensor and circuit
are confirmed to be OK, but the temperature display
is inoperative or incorrect, see the Trip Computer/
Compass/Display Module diagnosis in this group. For
circuit descriptions and diagrams, refer to 8W-45 -
Body Control Module and 8W-49 - Overhead Console
in Group 8W - Wiring Diagrams.
SENSOR TEST
(1) Turn the ignition switch to the Off position.
Unplug the temperature sensor connector.
8V - 3