Diagnosis And Testing; Service Procedures; Compass Calibration; Compass Variation Adjustment - Dodge ram truck 3500 1996 Service Manual

8V - 4 OVERHEAD CONSOLE SYSTEMS
mm
DIAGNOSIS AND TESTING (Continued)
continuity. I f OK, go to Step 6. I f not OK, repair the
short circuit as required.
(6) Check for continuity between the ambient tem­
perature sensor signal circuit cavity of the overhead
console connector and a good ground. There should
be no continuity. I f OK, see the Compass/Display
Module diagnosis in this group. I f not OK, repair the
short circuit as required.
S E R V I C E P R O C E D U R E S
COMPASS VARIATION ADJUSTMENT
Variance is the difference between magnetic north
and geographic north. I n some areas, the difference
between magnetic and geographic north is great
enough to cause the compass to give false readings. I f
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). .
Fig. 1 Variance Settings
(2) Turn the ignition switch to the On position.
(3) Depress both the US/Metric, and the Comp/
Temp buttons. Hold the buttons down until "VAR"
appears in the display module. This takes about five
seconds.
(4) Release both of the buttons. The zone number
will appear in the display module.
(5) Press and release the US/Metric button to step
through the zone numbers, until the zone number for
your area appears in the display.
(6) Press the Comp/Temp button to enter this zone
number into the compass unit memory.
(7) Confirm that the correct directions are now
indicated.
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.
NOTE: Whenever the compass is calibrated manu­
ally, the variation number must also be reset. See
the Compass Variation Adjustment procedure, in
this group.
Calibrate the compass manually as follows:
(1) Start the engine.
(2) Depress both the US/Metric and Comp/Temp
buttons. Hold down both buttons until "CAL" appears
in the display module. This takes about ten seconds,
and appears about five seconds after "VAR" is dis­
played.
(3) Release both buttons.
(4) Drive the vehicle on a level surface, away from
large metal objects, through three or more complete
circles in not less than 48 seconds. The "CAL" mes­
sage will disappear from the display to indicate that
the compass is now calibrated.
NOTE: If the "CAL" message remains in the dis­
play, either there is excessive magnetism near the
compass, or the unit is faulty. Repeat the demagne­
tizing and calibration procedures at least one more
time.