Diagnosis And Testing - Jeep 1997 Grand Cherokee Service Manual

8E - 10 INSTRUMENT PANEL SYSTEMS
DESCRIPTION AND OPERATION (Continued)
The PCM uses an input from the water-in-fuel sen-
sor in the fuel filter/water separator to determine
that excess water has accumulated in the diesel fuel.
The PCM then sends the proper message to the
instrument cluster on the CCD data bus to turn the
lamp on or off. Refer to Group 14 - Fuel Systems for
more information.

DIAGNOSIS AND TESTING

INSTRUMENT CLUSTER
All of the gauges and most of the indicator lamps
in the instrument cluster are controlled by messages
received by the instrument cluster circuitry on the
CCD data bus. Only the cluster illumination lamps,
anti-lock brake system lamp, turn signal indicator
lamps, and the master lighting indicator lamp (if the
vehicle is so equipped) are hard-wired in the gauge
cluster.
If an individual gauge or lamp is inoperative, see
the diagnostic procedure under the heading for that
gauge or lamp. For circuit descriptions and diagrams,
refer to 8W-40 - Instrument Cluster in Group 8W -
Wiring Diagrams. If more than one gauge or lamp is
inoperative, perform the following:
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, REFER TO GROUP 8M - PASSIVE RESTRAINT
SYSTEMS BEFORE ATTEMPTING ANY STEERING
WHEEL, STEERING COLUMN, OR INSTRUMENT
PANEL COMPONENT DIAGNOSIS OR SERVICE. FAIL-
URE TO TAKE THE PROPER PRECAUTIONS COULD
RESULT IN ACCIDENTAL AIRBAG DEPLOYMENT
AND POSSIBLE PERSONAL INJURY.
(1) Check the fuse in the junction block module. If
OK, go to Step 2. If not OK, replace the faulty fuse.
(2) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Remove the instrument cluster bezel and the cluster
assembly as described in this group.
(3) Connect the battery negative cable. Check for
battery voltage at the fused B(+) circuit cavity of the
cluster wire harness connector. If OK, go to Step 4. If
not OK, repair the open circuit from the fuse as
required.
(4) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Probe each ground circuit cavity of the cluster wire
harness connector. Check for continuity to a good
ground. There should be continuity. If OK, refer to
the proper Body Diagnostic Procedures manual for
further testing of the instrument cluster circuitry
and the CCD data bus with a DRB scan tool. If not
OK, repair the open circuit to ground as required.
COOLANT TEMPERATURE GAUGE
If the problem being diagnosed is related to gauge
accuracy, be certain to confirm that the problem is
with the gauge and not with cooling system perfor-
mance. The actual engine coolant temperature should
be checked with a test gauge or thermometer and
compared to the gauge readings before you proceed
with gauge diagnosis. Refer to Group 7 - Cooling Sys-
tem for more information. Refer to Group 8W - Wir-
ing Diagrams for circuit descriptions and diagrams.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, REFER TO GROUP 8M - PASSIVE RESTRAINT
SYSTEMS BEFORE ATTEMPTING STEERING WHEEL,
STEERING COLUMN, OR INSTRUMENT PANEL COM-
PONENT DIAGNOSIS OR SERVICE. FAILURE TO
TAKE THE PROPER PRECAUTIONS COULD RESULT
IN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSI-
BLE PERSONAL INJURY.
Diagnosis of the coolant temperature sensor and
circuit or the Powertrain Control Module (PCM)
should be performed with the DRB scan tool as
described in the proper Powertrain Diagnostic Proce-
dures manual. Diagnosis of the coolant temperature
gauge, the instrument cluster circuitry, or the CCD
data bus should be performed with the DRB scan tool
as described in the proper Body Diagnostic Proce-
dures manual.
FUEL GAUGE
If the problem being diagnosed is related to gauge
accuracy, be certain to confirm that the problem is
with the gauge or sending unit and not with the fuel
tank. Inspect the fuel tank for signs of damage or
distortion that could affect the sending unit perfor-
mance before you proceed with gauge diagnosis.
Refer to Group 8W - Wiring Diagrams for circuit
descriptions and diagrams.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, REFER TO GROUP 8M - PASSIVE RESTRAINT
SYSTEMS BEFORE ATTEMPTING STEERING WHEEL,
STEERING COLUMN, OR INSTRUMENT PANEL COM-
PONENT DIAGNOSIS OR SERVICE. FAILURE TO
TAKE THE PROPER PRECAUTIONS COULD RESULT
IN ACCIDENTAL AIRBAG DEPLOYMENT AND POSSI-
BLE PERSONAL INJURY.
Diagnosis of the fuel gauge sending unit and cir-
cuit or the Powertrain Control Module (PCM) should
be performed with a DRB scan tool as described in
the proper Powertrain Diagnostic Procedures man-
ual. Diagnosis of the fuel gauge, the instrument clus-
ter circuitry, or the CCD data bus should be
performed with the DRB scan tool as described in the
proper Body Diagnostic Procedures manual.
ZG