Power Locks: Description and Operation

Power Door Locks Description and Operation

Door Lock System Components

The power door lock system consists of the following components:

* Driver door module (DDM)
* Passenger door module (PDM)
* Door lock relay-Located in the instrument panel (I/P) fuse block and controls the locking of the rear doors.
* Door unlock relay-Located in the I/P fuse block and controls the unlocking of the rear doors
* Body control module (BCM)
* IP BEC
* Reversible door lock actuators in each door

Door Lock System Controls

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

* A power door lock or unlock switch command
* A keyless entry command
* An automatic door lock function
* Door lock cylinder switch command
* Lockout Prevention

Driver and Passenger 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 two-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 monitor these inputs and send a LAN message indicating a change in the switch position. Modules, that activate the power door lock motors, receive the LAN message and activate the motor in the appropriate direction to lock or unlock the vehicle doors. The body control module (BCM) upon receipt of a lock or unlock signal will control the rear door lock or unlock relays and also send a LAN message to the DDM and PDM to perform the commanded function.

The modules that activate the power door lock motors are:

* DDM (driver door lock actuator)
* PDM (passenger front door lock actuator)
* BCM (both rear door lock actuators)

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 doors are controlled by the BCM through the rear door lock/unlock relay which is incorporated onto the printed circuit board in the LH BEC. The BCM controls the unlock relay by providing ground to energize the coil and controls the lock relay by providing battery voltage to energize the relay coil. 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 feature is factory programmed to have all doors lock and unlock.

When the automatic door lock feature is programmed to control the door lock system, the driver door switch or passenger door switch will lock the vehicle doors if the following inputs are true:

* Ignition 1 input is active
* All door jamb switch inputs are inactive
* 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 and PDM will lock all doors again.

BCM will unlock all the doors when the transmission is shifted into PARK.

Lockout Prevention

The lockout prevention feature prevents the locking of the driver door if the ignition key is left in the ignition lock cylinder. If a lock command 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, DDM and PDM will lock the doors and then DDM will unlock the driver door.