Jeep 1997 Grand Cherokee Service Manual page 536

8N - 4 ELECTRICALLY HEATED SYSTEMS
DIAGNOSIS AND TESTING (Continued)
not change. If OK, go to Step 4. If not OK, repair the
circuit to ground as required.
(4) Connect the negative lead of the voltmeter to
the right side bus bar and touch each grid line at
midpoint C with the positive lead. A reading of
approximately six volts indicates a line is good. A
reading of zero volts indicates a break in the grid
line between midpoint C and the left side bus bar. A
reading of ten to fourteen volts indicates a break
between midpoint C and the right side bus bar. Move
the positive lead on the grid line towards the break
and the voltage reading will change as soon as the
break is crossed.
DEFOGGER SWITCH
For circuit descriptions and diagrams, refer to
8W-48 - Rear Window Defogger in Group 8W - Wir-
ing Diagrams.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, REFER TO
RESTRAINT SYSTEMS BEFORE ATTEMPTING ANY
STEERING WHEEL,
INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
SERVICE. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
(1) Disconnect and isolate the battery negative
cable. Remove the inboard instrument panel switch
pod and unplug the switch pod 10-way wire harness
connector.
(2) Check for continuity between the ground cir-
cuit cavity of the switch pod 10-way 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 as required.
(3) Connect two jumper wires to the inboard
switch pod as follows. Connect the ground circuit ter-
minal in the 10-way wire harness connector recepta-
cle on the back of the inboard switch pod housing to
a good ground. Connect the fused rear window defog-
ger relay output circuit terminal of the 10-way wire
harness connector receptacle to a 12-volt battery
feed. The defogger switch LED indicator should light.
If OK, go to Step 4. If not OK, replace the faulty
inboard switch pod.
(4) Check for continuity between the ground cir-
cuit and rear window defogger switch sense circuit
terminals of the 10-way wire harness connector
receptacle on the back of the inboard switch pod
housing. There should be momentary continuity as
the defogger switch button is depressed, and then no
continuity. If OK, go to Step 5. If not OK, replace the
faulty inboard switch pod.
GROUP 8M - PASSIVE
STEERING COLUMN,
(5) Unplug the white 24-way wire harness connec-
tor from the Body Control Module (BCM). Check for
continuity between the rear window defogger switch
sense circuit cavity of the inboard switch pod 10-way
wire harness connector and a good ground. There
should be no continuity. If OK, go to Step 6. If not
OK, repair the short circuit as required.
(6) Check for continuity between the rear window
defogger switch sense circuit cavities of the inboard
switch pod 10-way wire harness connector and the
BCM white 24-way wire harness connector. There
should be continuity. If OK, see the Defogger Relay
diagnosis in this group. If not OK, repair the open
circuit as required.
DEFOGGER RELAY
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, REFER
RESTRAINT SYSTEMS BEFORE ATTEMPTING ANY
STEERING WHEEL,
INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
OR SERVICE. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
RELAY TEST
The defogger relay is located in the junction block,
on the right cowl side panel below the instrument
panel in the passenger compartment. Remove the
defogger relay from the junction block as described in
this group to perform the following tests:
(1) A relay in the de-energized position should
have continuity between terminals 87A and 30, and
no continuity between terminals 87 and 30. If OK, go
to Step 2. If not OK, replace the faulty relay.
(2) Resistance between terminals 85 and 86 (elec-
tromagnet) should be 75
Step 3. If not OK, replace the faulty relay.
(3) Connect a battery to terminals 85 and 86.
There should now be continuity between terminals
30 and 87, and no continuity between terminals 87A
and 30. If OK, see the Relay Circuit Test in this
group. If not OK, replace the faulty relay.
RELAY CIRCUIT TEST
(1) The relay common feed terminal cavity (30) is
connected to battery voltage and should be hot at all
times. If OK, go to Step 2. If not OK, repair the open
circuit to the PDC fuse as required.
(2) The relay normally closed terminal (87A) is
connected to terminal 30 in the de-energized position,
but is not used for this application. Go to Step 3.
(3) The relay normally open terminal (87) is con-
nected to the common feed terminal (30) in the ener-
TO GROUP 8M -
STEERING COLUMN,
10 ohms. If OK, go to
ZG
PASSIVE
OR