B1640

DTC B1640 or B1645

Diagnostic Instructions

* Perform the Diagnostic System Check - Vehicle (Initial Inspection and Diagnostic Overview) prior to using this diagnostic procedure.
* Review Strategy Based Diagnosis (Initial Inspection and Diagnostic Overview) for an overview of the diagnostic approach.
* Diagnostic Procedure Instructions (Initial Inspection and Diagnostic Overview)provides an overview of each diagnostic category.



DTC Descriptors
DTC B1640 01
- Mirror Heater Circuit Short to Battery

DTC B1640 02
- Mirror Heater Circuit Short to Ground




Circuit/System Description

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 (Outside Mirror Description and Operation) .


Conditions for Running the DTC

Battery voltage must be between 9-16 volts.


Conditions for Setting the DTC

* DTC B1640 01 will set when the DDM or PDM detects a short to voltage in the heating element supply voltage.
* DTC B1640 02 will set when the DDM or PDM detects a short to ground in the heating element supply voltage circuit.



Actions Taken When the DTC Sets

The heated mirror function will be disabled.


Conditions for Clearing the DTC

* The condition responsible for setting the DTC no longer exists.
* You issue a scan tool CLEAR DTCs command.
* A history DTC will clear once 50 consecutive malfunction-free ignition cycles have occurred.



Reference Information
Schematic Reference

Outside Rearview Mirror Schematics (Outside Rearview Mirror Schematics)
Connector End View Reference

Component Connector End Views (Connector Views)
Electrical Information Reference

* Circuit Testing (Component Tests and General Diagnostics)
* Connector Repairs (Component Tests and General Diagnostics)
* Testing for Intermittent Conditions and Poor Connections (Component Tests and General Diagnostics)
* Wiring Repairs (Component Tests and General Diagnostics)

Scan Tool Reference

Control Module References (Programming and Relearning)for scan tool information.


Circuit/System Testing

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

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

3. Connect a test lamp between the control circuit and the ground circuit terminal.
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.



Repair Instructions

Perform the Diagnostic Repair Verification (Verification Tests) after completing the diagnostic procedure.

* Power Mirror Replacement (Power Mirror Replacement)
* Control Module References (Programming and Relearning)for DDM or PDM replacement, setup, and programming