Antitheft and Alarm Systems: Description and Operation

When the Theft Deterrent System has been turned on, or armed, it will automatically operate alarms. It sounds the vehicle Horns and flashes the Exterior Lights. This happens when any of the doors are opened.


Alarms

The Horn Alarm is operated by the Horn Relay. The coil of this Relay is grounded by the Solid State Theft Deterrent Controller to turn on the Relay. When the Relay contacts close, battery voltage is supplied to the Horn at the same time ground is applied to terminal 1D4 of the ECM to turn on the lights. The ECM commands the lights on and off through the Lighting Data Line. The Theft Deterrent Module then opens the relay coil circuit to turn off the alarms. The alarms will pulse on and off every second for 2 to 4 minutes after the system has been triggered by tampering or forced entry.


Arming

The arming sequence begins with the Ignition Switch turned OFF. This removes battery voltage at terminal K, the Ignition Input. As a door is opened ground is applied to terminal J, the Tamper Input. The system is not armed yet so grounding the Tamper Input does not set off the alarms. With a Door Lock Switch momentarily moved to LOCK, battery voltage is momentarily applied to terminal G, the System Arm Input. Lastly, closing all open doors will remove ground from terminal J and complete the arming sequence. The system is now armed.


Cancellation

The arming sequence can be cancelled. This is done by moving a Door Lock Switch to the UNLOCK position before the door is closed to complete the arming of the system. Battery voltage is applied momentarily to terminal M with the Door Switch in UNLOCK. This cancels the arming.


Disarming

When one of the doors is unlocked with a key, a grounding switch in the Door Lock Cylinder closes. This grounds terminal H of the Module, the Disarm Input. The system is disarmed and no alarms will operate when a door is opened. The ECM also grounds terminal H to disarm the system when the central door unlock feature is activated from the Trunk Lock Cylinder Switch. The system can also be disarmed if the alarms are not sounding by turning the Ignition to RUN. This applies battery voltage to terminal K. When the alarms are sounding, the system can only be disarmed from the Door and Trunk Lock Cylinder Switches.

Tampering

The alarms are set off when terminal J is grounded. The Door Jamb Switches close, grounding the Tamper Input when any door is open.


The Diode Array Module isolates the LH Front Door Jamb Switch. The Chime Module also uses the LH Front Door Jamb Switch. The Diode prevents the RH Door Jamb Switch in the Theft Deterrent System from operating the key in the Ignition warning.