Service Procedures; Compass Calibration; Compass Variation Adjustment - Jeep 1997 Grand Cherokee Service Manual

8V - 4 OVERHEAD CONSOLE SYSTEMS
DIAGNOSIS AND TESTING (Continued)
and thermometer display module display. The sensor
is mounted outside the passenger compartment near
the front and center of the vehicle.
If any portion of the ambient temperature sensor
circuit fails, the thermometer display will self-diag-
nose the circuit. An "SC" (short circuit) will appear in
the display 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 the display in place of the tem-
perature, when the sensor is exposed to temperatures
below -40° C (-40° F), or if the sensor circuit is open.
The ambient temperature sensor circuit can also be
diagnosed using the following Sensor Test, and Sen-
sor Circuit Test. If the temperature sensor and cir-
cuit are confirmed to be OK, but the temperature
display is inoperative or incorrect, see the Trip Com-
puter, Compass, and Thermometer 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 wire harness connec-
tor.
(2) Measure the resistance of the temperature sen-
sor. At -40° C (-40° F), the sensor resistance is 336
kilohms. At 55° C (140° F), the sensor resistance is
2.488 kilohms. The sensor resistance should read
between these two values. If OK, go to the Sensor
Circuit Test. If not OK, replace the faulty sensor.
SENSOR CIRCUIT TEST
(1) Turn the ignition switch to the Off position.
Disconnect and isolate the battery negative cable.
Unplug the ambient temperature sensor wire har-
ness connector and the black 24-way Body Control
Module (BCM) wire harness connector.
(2) Connect a jumper wire between the two termi-
nals in the body half of the sensor wire harness con-
nector.
(3) Check for continuity between the sensor return
circuit and the ambient temperature sensor signal
circuit cavities of the black 24-way BCM wire har-
ness connector. There should be continuity. If OK, go
to Step 4. If not OK, repair the open circuit as
required.
(4) Remove the jumper wire from the ambient tem-
perature sensor wire harness connector. Check for
continuity between the sensor return circuit cavity of
the black 24-way BCM wire harness connector and a
good ground. There should be no continuity. If OK, go
to Step 5. If not OK, repair the short circuit as
required.
(5) Check for continuity between the ambient tem-
perature sensor signal circuit cavity of the black
24-way BCM wire harness connector and a good
ground. There should be no continuity. If OK, see the
Trip Computer, Compass, and Thermometer Display
Module diagnosis in this group. If not OK, repair the
short circuit as required.

SERVICE PROCEDURES

COMPASS VARIATION ADJUSTMENT

Variance is the difference between magnetic north
and geographic north. In some geographic locations,
the difference between magnetic and geographic
north is great enough to cause the compass to give
false readings. If this problem occurs, the compass
variance must be set.
To set the compass variance:
(1) Using the Variance Settings map, find your
geographic location and note the zone number (Fig.
1).
(2) Turn the ignition switch to the On position. If
the compass/temperature data is not currently being
displayed, momentarily depress and release the Step
button to step through the display options until you
have reached the compass/temperature display.
(3) Depress both the U.S./Metric, and the Step but-
tons. Hold the buttons down until "VAR" appears in
the display. This takes about five seconds.
(4) Release both of the buttons. The current vari-
ance zone number setting will appear in the display.
(5) Press and release the U.S./Metric button to
step through the zone numbers, until the zone num-
ber for your geographic location appears in the dis-
play.
(6) Press the Step button to enter this zone num-
ber into the compass unit memory.
(7) Confirm that the correct directions are now
indicated by the compass.

COMPASS CALIBRATION

CAUTION: Do not place any external magnets, such
as magnetic roof mount antennas, in the vicinity of
the compass. Do not use magnetic tools when ser-
vicing the overhead console.
The electronic compass unit features a self-cali-
brating design, which simplifies the calibration pro-
cedure. This feature automatically updates the
compass calibration while the vehicle is being driven.
This allows the compass unit to compensate for small
changes in the residual magnetism that the vehicle
may acquire during normal use. Do not attempt to
calibrate the compass near large metal objects such
as other vehicles, large buildings, or bridges.
ZG