The outside rearview mirrors heat during the defrost/defog cycles for the rear window. The heated mirrors are connected to the driver door module (DDM) and the passenger door module (PDM). The DDM and the PDM receive a GMLAN serial data message from the HVAC control module indicating the rear defogger has been activated. The DDM and PDM examine information from the body control module (BCM) to determine if vehicle conditions are correct for the heated mirrors function to be activated. If conditions are correct, the DDM and PDM will command there respective heated mirrors ON. For more detailed information concerning power mirror operation refer to Outside Mirror Description and Operation .

Schematic Reference

Outside Rearview Mirror Schematics

Connector End View Reference

Mirror Connector End Views

Electrical Information Reference

Scan Tool Reference

1. Ignition OFF, disconnect the harness connector at the inoperative outside rearview mirror heater element.
2. Test for less than 1.0 ohm of resistance between the heater element ground circuit and ground.

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

3. Connect a test lamp between the heater element control circuit and ground circuit.
4. Command the inoperative mirror heater ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.

⇒	If the test lamp is always ON, test the control circuit for a short to voltage. If the circuit tests normal, replace the inoperative door control module.

⇒	If the test lamp is always OFF, test the control circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the inoperative door control module.

5. If all circuits test normal, test or replace the inoperative outside rearview mirror.

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.