Circuit/System Description
WARNING: This page is about a different car, the 2012 Buick Verano. However, it is still accessible from the selected car via links, so may be relevant.
The exterior driver door handle contains a small sensor which allows the driver to lock the vehicle doors from the outside without using the remote keyless transmitter. The keyless entry control module supplies a 12V signal to the driver door handle switch signal circuit, when the sensor is touched, the circuit is grounded and the voltage in the signal circuit will drop. The keyless entry control module will detect the viltage drop and will then send a serial data message to the BCM to command all the doors to lock.