Power Locks: Description and Operation

Circuit Operation

Door Lock System Components
The power door lock system consists of the following components:
- Driver Door Module (DDM)
- Passenger Door Module (PDM)
- Liftgate Module (LGM)
- Door lock relay
- Door unlock relay
- Body Control Module (BCM)
- Reversible door lock actuators in each of the doors
- LR/RR LOCKS 10 A fuse (relay supply voltage)
- Door lock switches in driver and passenger doors (switches are integral components to the DDM and PDM)

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 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 modules which activate the power lock motors are:
- DDM (driver door lock actuator).
- PDM (passenger front door lock actuator).
- BCM (both rear door lock actuators).
- LGM (liftgate door lock actuator).

The DDM, PDM and LGM 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 passengers 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.