Body Control Module (BCM)

SYSTEM DESCRIPTION
The following actions cue the Body Control Module (BCM) type 4 to activate the headlamps and the horn:
^ The keyless entry Systems Remote Control Door Lock Receiver (RCDLR) sends a message to activate the alarm mode.
^ The BCM detects a theft attempt when the content theft deterrent is in either the armed or warning mode.
^ The theft deterrent system is in the trunk open mode.

The BCM interfaces with the horn through the horn relay. The horn relay allows the BCM to sound the horn in order to provide an audio alert. The BCM energizes the horn relay, causing the horn to sound by grounding CKT 28 during the following modes:
^ The armed mode
When the content theft deterrent is in the armed mode, the BCM sounds the horn once for 23-27 ms. The BCM sounds the horn only if the remote activation verification is in either mode 3 or 4. Refer to Body Control Module Diagnostic Information. The headlamps also turn on during this mode. The BCM will sound the horn first then the headlamps will flash once.
^ The warning mode
The warning mode attempts to warn away potential intruders prior to setting off the alarm mode. The headlamps will cycle ON and OFF 5 times at a rate of 0.9-1.1 Hz with a 20-25% active state duty cycle. The headlamps also turn ON and OFF 5 times during this mode. although the BCM alternates between the horn and the headlamps.
^ The alarm mode
When the content theft deterrent is in the alarm mode, the BCM sounds the horn ON and OFF for 2 minutes or until the alarm is disarmed at a rate of 0.9-1.1 Hz with a 20-25% active state duty cycle. The headlamps also turn ON during this mode although the BCM alternates between the horn and the headlamps.
^ The trunk open mode
This mode warns the vehicle operator that the content theft deterrent is waiting for the trunk to be closed before going into an armed mode. After the BCM sounds the horn for 23-27 ms. The BCM sounds the horn only if the remote activation verification is in either the 3 or 4 mode. Refer to Body Control Module Diagnostic Information. After the horn sounds the headlamps are turned ON for 950-1000 ms. This activation only takes place if the remote activation verification is in mode 2, 3 or 4.

CONDITIONS FOR SETTING THE DTC
The BCM detects a short to B+ or ground in CKT 28.

ACTION TAKEN WHEN THE DTC SETS
^ The BCM sets the Diagnostic Trouble Code (DTC) 7.
^ If CKT 28 is shorted to B+, the BCM does not sound the horn during the following modes:
- The armed mode
- The warning mode
- The alarm mode The trunk open mode
^ If CKT 28 is shorted to ground, the horn will sound all the time.

CONDITIONS FOR CLEARING THE DTC
^ A short to B+ or ground in CKT 28 is no longer present between the BCM and the horn relay.
^ After the repairs are completed, refer to Body Control Module Diagnostic Information

DIAGNOSTIC AIDS
^ Inspect for a short to B+ or ground in CKT 28.
^ A faulty horn relay.
^ Perform the following test while moving the wiring and connectors. This will cause the malfunction to appear.

REMOTE ACTIVATION VERIFICATION MODES
Perform the following procedure in order to change the remote activation verification mode:
1. Turn the IP dimmer switch OFF.
2. Turn the ignition switch to the OFF position.
3. Remove the MALL PGM fuse.
4. Turn the ignition switch to the ACC position.
^ The BCM will sound a chime the number of times equivalent to the BCM type installed on the vehicle.
^ The BCM has entered the feature customization mode.
^ In order to change the remote activation verification mode, press the lock button on the keyless entry transmitter.
^ The BCM will sound a chime the number of times equivalent to the remote activation verification mode.

The following are the remote activation verification modes:
^ Mode 1
The remote activation verification is disabled. The horn and headlamps are not activated.
^ Mode 2
The headlamps will flash when the doors are locked or unlocked using the keyless entry transmitter.
^ Mode 3
The headlamps will flash when the doors are unlocked using the keyless entry transmitter. The headlamps will flash and the horn will sound when the doors are locked using the keyless entry transmitter.
^ Mode 4
The headlamps will flash when the doors are locked or unlocked using the keyless entry transmitter.
The headlamps will flash and the horn will sound when the doors are locked using the keyless entry transmitter a second time within 5 seconds of locking the doors with the keyless entry transmitter.

BCM INPUT/OUTPUT TEST PROCEDURE
1. Turn the P dimmer switch OFF.
2. Turn the ignition switch to the OFF position.
3. Remove the MALL PGM fuse.
4. Turn the ignition switch to the ACC position. The BCM will sound a chime the number of times equivalent to the BCM type installed on the vehicle.
5. Within 1 second, turn the ignition switch from the ACC position, to the OFF position then back to the ACC position.
The BCM will sound any DTCs that are stored.
6. Turn the IP dimmer switch to the DOME position. The BCM enters the Input/Output test. There are 7 steps in the Input/Output test:
^ Test 1 de-energizes CKT 1393 (protected courtesy lamp output).
^ Test 2 energizes CKT 1393.
^ Test 3 grounds CKT 690 (courtesy lamps control).
^ Test 4 energizes the theft deterrent relay for 1 second by grounding CKT 352 and turns on the headlamps (BCM type 4 only).
^ Test 5 energizes the horn relay for 25 ms by grounding CKT 28 and sounds the horn (BCM type 4 only).
^ Test 6 turns on the theft deterrent indicator lamp by grounding CKT 749 (BCM type 4 only).
^ Test 7 turns off the theft deterrent indicator lamp by opening CKT 749 (BCM type 4 only).

The BCM completes the steps of the Input/Output test in numerical order.

In order to move to the next test, cycle the IP dimmer switch from DOME to OFF then back to DOME. The BCM will sound a chime a number of times equivalent to the Input/Output test number above. The Input/Output test sequence repeats until the ignition switch is turned to the OFF position.

Diagnostic Chart (Part 1 Of 2):

Diagnostic Chart (Part 2 Of 2):

TEST DESCRIPTION
The number(s) below refer to the step number(s) on the diagnostic table.
1. Always perform the BCM diagnostic system check before attempting to diagnose this DTC.
2. This step checks the operation of the horn system.
3. This step determines whether the BCM is faulty and not due to an intermittent malfunction.
4. This step checks for a B+ in CKT 28.
5. This step checks for a short to ground in CKT 28
6. This step determines if the malfunction is intermittent and not currently present.