Jeep 1997 Grand Cherokee Service Manual page 456

8G - 2 HORN SYSTEMS
DESCRIPTION AND OPERATION (Continued)
BODY CONTROL MODULE
A Body Control Module (BCM) is used on this
model to control and integrate many of the electronic
functions and features included on the vehicle. The
BCM contains a central processing unit and inter-
faces with other modules in the vehicle on the
Chrysler Collision Detection (CCD) data bus network.
The CCD data bus network allows the sharing of
sensor information. This helps to reduce wire har-
ness complexity, reduce internal controller hardware,
and reduce component sensor current loads. At the
same time, this system provides increased reliability,
enhanced diagnostics, and allows the addition of
many new feature capabilities.
The horn system is one of the outputs of the BCM.
The BCM is programmed to energize or de-energize
the horn relay in response to certain inputs from the
Vehicle Theft Security System (VTSS) and the
Remote Keyless Entry (RKE) system. Refer to Group
8P - Power Lock Systems for more information on the
RKE system. Refer to Group 8Q - Vehicle Theft/Secu-
rity Systems for more information on the VTSS.
The BCM is mounted under the driver side out-
board end of the instrument panel, behind the instru-
ment panel support
outboard switch pod. Refer to Group 8E - Instrument
Panel Systems for the removal and installation pro-
cedures. 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 autho-
rized electronic repair station. Refer to the latest
Warranty Policies and Procedures manual for a cur-
rent listing of authorized electronic 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
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.
RELAY TEST
The horn relay is located in the Power Distribution
Center (PDC) in the engine compartment. Refer to
armature and below
GROUP 8M - PASSIVE
STEERING COLUMN,
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
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.
the
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-
gized position. This terminal supplies battery voltage
OR
to the horn(s). There should be continuity between
the cavity for relay terminal 87 and the horn relay
output circuit cavity of each horn wire harness con-
nector 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.
NUMBER TERMINAL LEGEND COMMON FEED IDENTIFICATION
COIL GROUND
COIL BATTERY
NORMALLY OPEN
NORMALLY CLOSED
5 ohms. If OK, go to Step
Horn Relay
ZG