Rear Glass Heating Grid Diagnosis And Testing; Defogger Switch Diagnosis And Testing; Defogger Relay Diagnosis And Testing - Jeep Cherokee 2000 Service Manual

8N - 4 ELECTRICALLY HEATED SYSTEMS
DIAGNOSIS AND TESTING (Continued)
REAR GLASS HEATING GRID
For circuit descriptions and diagrams, refer to
8W-48 - Rear Window Defogger in Group 8W - Wir-
ing Diagrams. To detect breaks in the grid lines, the
following procedure is required:
(1) Turn the ignition switch to the On position. Set
the defogger switch in the On position. The indicator
lamp should light. If OK, go to Step 2. If not OK, see
the Defogger Relay diagnosis in this group.
(2) Using a 12-volt DC voltmeter, contact the ver-
tical bus bar on the right side of the vehicle with the
negative lead. With the positive lead, contact the ver-
tical bus bar on the left side of the vehicle. The volt-
meter should read battery voltage. If OK, go to Step
3. If not OK, repair the open circuit to the defogger
relay as required.
(3) With the negative lead of the voltmeter, contact
a good body ground point. The voltage reading should
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 accessory switch bezel from the
instrument panel and unplug the defogger switch
wire harness connector.
(2) Check for continuity between the ground cir-
cuit cavity of the defogger switch wire harness con-
nector and a good
continuity. If OK, go to Step 3. If not OK, repair the
open circuit as required.
GROUP 8M - PASSIVE
STEERING COLUMN,
ground. There should
(3) Check for continuity between the ground cir-
cuit terminal and the rear window defogger switch
sense circuit terminal on the back of the defogger
switch housing (Fig. 2). There should be momentary
continuity as the defogger switch button is depressed,
and then no continuity. If OK, see the diagnosis for
the Instrument Cluster in this group. If not OK,
replace the faulty switch.
SWITCH POSITION
OFF
ON
ILLUMINATION LAMP
INDICATOR LAMP
Fig. 2 Defogger Switch Continuity
DEFOGGER RELAY
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS, REFER
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
OR
INJURY.
RELAY TEST
The defogger relay (Fig. 3) is located in the junc-
tion block, on the right cowl side inner panel below
the instrument panel in the passenger compartment.
Remove the defogger relay from the junction block 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.
be
(2) Resistance between terminals 85 and 86 (elec-
tromagnet) should be 75
Step 3. If not OK, replace the faulty relay.
CONTINUITY BETWEEN
LAMPS
MOMENTARY 1 AND 2
1 AND 4
1 AND 3
TO GROUP 8M -
STEERING COLUMN,
10 ohms. If OK, go to
XJ
PASSIVE
OR