Power Locks: Description and Operation
POWER DOOR LOCKS DESCRIPTION AND OPERATIONDOOR 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 rear door lock switch
- The door lock relay
- The door unlock relay
- The reversible door lock actuators in each of the doors
- LOCKS 20A fuse (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
POWER DOOR LOCK OPERATION
The front power door lock switches are integral components of the DDM and 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 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 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 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 doors and lift gate 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.