The key cylinder switch contains a signal circuit and a low reference circuit. When the door key is turned to unlock, the switch contacts, which are normally open, close and the driver door module (DDM) detects a switched ground. The DDM sends a message via GMLAN serial data to the passenger door module (PDM), and body control module (BCM) to lock or unlock there respective doors.

Schematic Reference

Door Lock/Indicator Schematics

Connector End View Reference

Vehicle Access Connector End Views

Electrical Information Reference

Scan Tool Reference

1. Ignition OFF, disconnect the harness connector at the driver door lock switch.
2. Ignition OFF, scan tool OFF, test for less than 10.0 ohms of resistance between the low reference circuit terminal B and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance.

3. Ignition ON, verify the scan tool door key cyl. unlock switch parameter is IDLE.

⇒	If not the specified value, test the signal circuit terminal A for a short to ground. If the circuit tests normal, replace the DDM.

4. Install a 3-A fused jumper wire between the signal circuit terminal A and the low reference circuit terminal B. Verify the scan tool door key cyl. unlock switch parameter is UNLOCK.

⇒	If not the specified value, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the DDM.

5. If the circuits test normal, test or replace the driver door lock switch.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.