GM Service Manual Online
For 1990-2009 cars only

Door Lock System Components

The power door lock system consists of the following components:

    • The driver door module (DDM)
    • The passenger door module (PDM)
    • The body control module (BCM)
    • The driver information center (DIC)
    • The rear door lock switch
    • The door lock relay
    • The door unlock relay
    • The reversible door lock actuators in each of the doors and liftgate
    • LOCKS 20A fuse (rear lock/unlock relay supply voltage)

Door Lock System Controls

The power door lock system can be controlled by any of the following:

    • A power door lock or unlock switch activation
    • A keyless entry transmission
    • An automatic door lock function
    • A delay lock function
    • Door lock cylinder switch activation
    • Lockout Prevention
    • An airbag deployment

Driver, Passenger and Cargo Door Lock System Operation

The front power door lock switches are integral components of the driver door module (DDM) and passenger door module (PDM). The switches are 2 position normally open rocker switches. When placed in either the lock or unlock positions, the switches provide a direct input to the DDM or PDM. The DDM or PDM monitors these inputs and sends a Class 2 message indicating a change in the switch's respective position. Modules which activate the power door lock motors receive the Class 2 message and activate the motor in the appropriate direction to lock or unlock the vehicle's doors and liftgate. The rear door lock switch provides a lock and unlock signal to the body control module (BCM). The BCM upon receipt of a lock or unlock signal will control the rear door lock relays and also send a Class 2 message to the DDM and PDM to perform the appropriate function.

The modules which activate the power lock motors are:

    • The DDM (driver door lock actuator)
    • The PDM (passenger front door lock actuator)
    • The BCM (both rear door lock actuators and cargo door/liftgate)

The DDM and PDM are directly connected to the respective door lock actuator through the door lock motor lock and unlock circuits. Once a door lock or unlock request has been received, the module will supply battery voltage to one side of the actuator and ground the other causing the doors to lock or unlock.

The rear passenger and cargo doors differ slightly in that they use lock and unlock relays. The relays supply and coil sides receive a constant voltage through the battery voltage supply circuit. The normally closed contacts are connected to ground and the control side is connected to the BCM. Once a door lock or unlock request has been received by the BCM, the BCM will ground the control side of the appropriate relay. This energizes the relay and allows voltage to be applied to either the door lock motor lock or unlock circuits. since the other side of the door lock actuator is connected to the normally closed contacts of the opposing relay to ground, the doors lock or unlock.

Programmable Automatic Door Locks

The automatic door lock feature can be programmed to control the door lock system. The automatic door lock feature is factory programmed to have all doors lock and unlock. For detailed instructions on programming the automatic door locks, refer to the owners manual.

When the automatic door lock feature is programmed to control the door lock system, the driver door module (DDM), passenger door module (PDM) and body control module (BCM) will lock the vehicle doors if the following inputs are true:

    • The ignition 1 input is active.
    • All door jamb switch inputs are inactive.
    • The cargo door or liftgate/liftglass ajar inputs are inactive.
    • The transmission is shifted out of PARK.

This automatic door lock function will only occur once per ignition cycle unless, a door jamb switch input changes state to active and back to inactive. Then the DDM, PDM and BCM will lock all doors again.

Once the automatic door lock feature has locked the doors, the BCM will then unlock all the doors when the transmission is shifted into PARK.

Lockout Prevention

This feature prevents the locking of the driver door if the ignition key is left in the ignition lock cylinder. If a lock function occurs from any door lock switch and the body control module (BCM) senses an active state on either the left front door latch signal, secondary door latch switch signal and/or the liftgate ajar switch signal circuits and the key in ignition switch signal circuit is in the YES state, the BCM, driver door module (DDM) and passenger door module (PDM) will lock the doors and then the DDM will unlock the driver door.

Delayed Locking Operation

With any door open and a door lock switch is activated in the lock position, the driver door module (DDM), passenger door module (PDM) and the body control module (BCM) will go into a lock pending state. The BCM will also give 3 audible chimes. When the door is closed, the DDM, PDM and the BCM will lock the doors after approximately 5 seconds. This feature can be overridden by activating the door lock switch a second time and the doors will lock even with a door open.

Unlock After Air Bag Deployment

This feature will unlock all of the vehicle doors 15 seconds after an air bag deployment.