Diagnosis And Testing; Thermometer; Trip Computer, Compass, And; Thermometer Display Module - Jeep 1997 Grand Cherokee Service Manual

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DESCRIPTION AND OPERATION (Continued)
door are selected and mounted on a post in the cen-
ter of the storage bin door. The peg(s) selected and/or
the post must be long enough to depress the button
of the transmitter, when the garage door opener stor-
age bin door is depressed. The pegs may be stacked,
if necessary. Refer to the owner's manual in the vehi-
cle glove box for more information.
SUNGLASSES STORAGE BIN
A sunglasses storage bin is included in the long-
type overhead console. The interior of the bin is cov-
ered with a flocking material to protect the
sunglasses from being scratched. This bin features a
push/push-type latching mechanism, and a viscous
dampening system for a fluid opening action.

DIAGNOSIS AND TESTING

TRIP COMPUTER, COMPASS, AND

THERMOMETER DISPLAY MODULE

If the problem with the trip computer, compass,
and thermometer display module is an inaccurate or
scrambled display, use the Self-Diagnostic Test proce-
dures. 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 wire harness
connector and a good ground. There should be conti-
nuity. If OK, go to Step 3. If not OK, repair the open
circuit to ground as required.
(3) Check for battery voltage at the fused B(+) cir-
cuit cavity of the overhead console wire harness con-
nector. 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 circuit cavity of the overhead console wire
harness 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
wire harness connector and the junction block recep-
tacle for the courtesy lamp relay. There should be
continuity. If OK, proceed to the Self-Diagnostic Test
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.
OVERHEAD CONSOLE SYSTEMS
SELF-DIAGNOSTIC TEST
A self-diagnostic test is used to determine that the
trip computer, compass, thermometer, and all of the
display module segments are operating properly elec-
trically. 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) Respond to the respective test results as fol-
lows. If all tests are passed, the module will automat-
ically return to normal operation.
d. In the display segment test, if any segment
should fail to light the unit is faulty and must be
replaced.
e. If the internal circuitry test is failed, the module
will display "FAIL". If "FAIL" is displayed, the unit is
faulty and must be replaced.
f. If the CCD data bus message test is failed, the
module will display "CCD". If "CCD" is displayed, the
use of a DRB scan tool and the proper Body Diagnos-
tic Procedures manual are required for further diag-
nosis.
(5) Momentarily depress and release either button
one time to exit the self-diagnostic test mode and
return the trip computer, compass, and thermometer
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 ambi-
ent temperature sensor, a wiring circuit, the Body
Control Module (BCM), the CCD data bus, and a por-
tion of the overhead console trip computer, compass,
8V - 3