Driver and Passenger Door Unlock Operation (Base Vehicles)
WARNING: This page does not describe the selected car, but rather 7 other vehicles, including the 2002 GMC Yukon XL, 2002 GMC Yukon, 2002 Chevrolet Tahoe, 2002 Chevrolet Suburban, and 2002 Chevrolet Avalanche. However, it is still accessible from the selected car via links, so may be relevant.
When any of the door lock switches are placed in the unlock position, voltage is applied to the door unlock signal circuit and the BCM. When the BCM senses the voltage signal, it grounds the door unlock control circuit and the unlock relay winding. Since the other side of the unlock relay winding is connected to battery voltage, the relay is energized. This causes the contacts to close and complete the path from the DR LOCK fuse through the battery voltage circuit. Voltage is then applied through the UNLOCK fuse to the unlock side of the door lock actuators. Since the other side of the door lock actuators are connected to the normally closed contacts of the lock relay to ground, the doors unlock.