Door Ajar Switches
WARNING: This page is about a different car, the 2007 GMC Sierra and 2007 Chevrolet Silverado. However, it is still accessible from the selected car via links, so may be relevant.
The CTD system uses the door ajar switches as a status indicator to activate the alarm. The BCM receives the status of the front door ajar switches based on serial data messages from the Driver Door Module (DDM) and Passenger Door Module (PDM). The rear door ajar switches are monitored via a discrete input from each door ajar switch. If the BCM receives a ground signal from a door ajar switch when the CTD system is armed, the BCM activates the alarm.