Jeep 1996 Grand Cherokee, Service Manual

Page: 343 / 1551

The horn system is one of the outputs of the BCM.
The BCM is programmed to energize the horn relay
in response to certain inputs from the Vehicle Theft
Security System (VTSS) system or the Remote Key-
less Entry (RKE) system. Refer to Group 8P - Power
Lock Systems for more information on the RKE sys-
tem. Refer to Group 8Q - Vehicle Theft/Security Sys-
tems for more information on the VTSS system.
The BCM is mounted under the left end of the
instrument panel, behind the instrument panel sup-
port armature and below the left switch pod. Refer to
Group 8E - Instrument Panel Systems for removal
and installation procedures. For diagnosis of the
BCM or the CCD data bus, refer to the proper Body
Diagnostic Procedures Manual. The BCM can only be
serviced by an authorized repair station. Refer to the
Warranty Policies and Procedures Manual for a list-
ing of authorized repair stations.
DIAGNOSIS AND TESTING
HORN RELAY
For circuit descriptions and diagrams, refer to
8W-41 - Horns/Cigar Lighter in Group 8W - Wiring
Diagrams.
WARNING: ON VEHICLES EQUIPPED WITH AIR-
BAGS,
REFER TO GROUP 8M - PASSIVE
RESTRAINT SYSTEMS BEFORE ATTEMPTING
STEERING WHEEL, STEERING COLUMN, OR
INSTRUMENT PANEL COMPONENT DIAGNOSIS OR
SERVICE. FAILURE TO TAKE THE PROPER PRE-
CAUTIONS COULD RESULT IN ACCIDENTAL AIR-
BAG DEPLOYMENT AND POSSIBLE PERSONAL
INJURY.
RELAY TESTS
The horn relay is located in the Power Distribution
Center (PDC) in the engine compartment. Refer to
the PDC label for horn relay identification and loca-
tion.
Remove the horn relay from the PDC 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
6
5 ohms. If OK, go to 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 TESTS
(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-
gized position. This terminal supplies battery voltage
to the horn(s). There should be continuity between
the cavity for relay terminal 87 and the horn(s) feed
terminal(s) at all times. If OK, go to Step 4. If not
OK, repair the open circuit to the horn(s) as
required.
(4) The coil battery terminal (86) is connected to
the electromagnet in the relay. It is connected to bat-
tery voltage and should be hot at all times. Check for
battery voltage at the cavity for relay terminal 86. If
OK, go to Step 5. If not OK, repair the open circuit to
the PDC fuse as required.
(5) The coil ground terminal (85) is connected to
the electromagnet in the relay. It is grounded
through the horn switch when the horn switch is
depressed. It can also be grounded by the body con-
trol module in response to inputs from the vehicle
theft alarm or remote keyless entry systems. Check
for continuity to ground at the cavity for relay termi-
nal 85. There should be continuity with the horn
switch depressed, and no continuity with the horn
switch released. If not OK, see the diagnosis for the
Horn Switch in this group.
HORN SWITCH
For circuit descriptions and diagrams, refer to
8W-41 - Horns/Cigar Lighter in Group 8W - Wiring
Diagrams.
Horn Relay
8G - 2 HORN SYSTEMS
ZJ
DESCRIPTION AND OPERATION (Continued)