This is right from the Xfire Service Manual:

"OPERATION
The power lock system is operated with pneumatic supply lines connected to actuators at each power lock. Locking and unlocking is accomplished when the Body Control Module (BCM) is actuated by the Sentry Key Remote Entry Module (SKREEM). The BCM in turn transmits a signal to the Central Locking Pump/Security System Module via the Controller Area Network (CAN) bus. Then Central Locking Pump/Security System Module incorporates a pump to supply pressure or vacuum and valves which direct the supply via pneumatic supply lines to the power lock system component."

In another section, the manual describes:
"The power lock actuators are controlled by pneumatic supply lines that transfer either vacuum or pressure from the Central Locking Pump/Security System Module to the component through distributors.".


Nowhere, could I find reference to Hydraulic Fluid and such; this sounds like it is air / vacuum transfer in the pneumatic lines.