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DTC B1020

DTC B1020

Diagnostic Instructions


• Perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

• Review Strategy Based Diagnosis for an overview of the diagnostic approach.

• Diagnostic Procedure Instructions provides an overview of each diagnostic category.


DTC Descriptor

DTC B1020 00

Auxiliary Electronic Control Unit (ECU) Performance

Circuit/System Description

The HVAC control module communicates with the radio/HVAC control via serial data. This DTC indicates a fault in the radio/HVAC control. No external circuits are involved. The HVAC may continue to respond normally to valance panel functions when this DTC is set.

Conditions for Running the DTC


• Ignition is ON or in the ACC position.

• The system voltage is at least 9.5 V and no more than 15.5 V.

• All the above conditions are present for greater than 10 seconds.


Conditions for Setting the DTC

The HVAC control module receives an improper status response indicating an internal ECU fault in the radio/HVAC control.

Action Taken when the DTC Sets

No action is taken.

Conditions for Clearing the DTC


• A current DTC clears when the HVAC control module receives a proper status response message back from the HVAC control assembly.

• A history DTC clears after 50 malfunction-free ignition cycles.


Diagnostic Aids


• This DTC may be stored as a history DTC without affecting the operation ofthe radio/HVAC control.

• If stored only as a history DTC and not retrieved as a current DTC, do not replace the radio/HVAC control.

• If this DTC is retrieved as both a current and history DTC, replace the radio/HVAC control.


Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

Component Connector End Views

Description and Operation

Automatic HVAC Description and Operation

Electrical Information Reference


• Circuit Testing

• Connector Repairs

• Testing for Intermittent Conditions and Poor Connections

• Wiring Repairs


Scan Tool Reference

Control Module References for scan tool information

Circuit/System Verification

If this DTC is retrieved as a current DTC, replace the radio/HVAC control.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.

Control Module References for radio/HVAC control replacement, setup, and programming