Diagnostic Instructions

DTC Descriptors

DTC B3779 05: Air Flow Control 9 Feedback Circuit Short to Battery or Open

DTC B3779 06: Air Flow Control 9 Feedback Circuit Short to Ground or Open

DTC B3779 08: Air Flow Control 9 Feedback Circuit Signal Invalid

Diagnostic Fault Information

Circuit	Short to Ground	Open/High Resistance	Short to Voltage	Signal Performance
Mode Door Control A Circuit	1	1	1	--
Mode Door Control B Circuit	1	1	1	--
Mode Door Position Signal	B3779 05	B3779 06 B3779 05	B3779 06	B3779 08
Mode Door 5-Volt Reference Circuit	B3779 05	B3779 06 B3779 05	B3779 06	B3779 08
Mode Door Low Reference Circuit	--	1	1	--
1. Mode Door Actuator Inoperative

Circuit/System Description

The HVAC control module controls the HVAC door actuators to regulate the airflow through the HVAC system. Each actuator consists of an electric motor and a potentiometer. The module supplies a low reference and 5-volt reference source voltage to the potentiometer. The HVAC control module monitors the voltage drop across the potentiometer on the door position signal circuit. When the actuator shaft rotates, the voltage on the door position signal circuit changes. The HVAC control module supplies the actuator motor with a 12-volt control circuit and a ground control circuit. The HVAC module controls the direction of the actuator door by changing the polarity of the control circuits.

Conditions for Running the DTC

Conditions for Setting the DTC

The actual mode door position differs from the commanded door position.

Action Taken When the DTC Sets

Driver A and driver B circuits are deactivated for the mode door actuator.

Conditions for Clearing the DTC

Reference Information

Schematic Reference

HVAC Schematics

Connector End View Reference

HVAC Connector End Views

Electrical Information Reference

Scan Tool Reference

Circuit/System Testing

1. Ignition OFF, disconnect the recirculation actuator harness connector at the recirculation actuator.
2. Test for less than 1.0 ohm of resistance between the low reference circuit terminal 1 and ground.

⇒	If greater than the specified range, test the low reference circuit for an open/high resistance. If the circuit tests normal, replace the HVAC control module.

3. Ignition ON, test for 4.8-5.2 volts between the 5-volt reference circuit terminal 3 and ground.

⇒	If less than the specified range, test the 5-volt reference circuit for a short to ground or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

⇒	If greater than 5.2 volts, test the 5-volt reference circuit for a short to voltage. If the circuit tests normal, replace the HVAC control module.

4. Verify the appropriate scan tool parameter is less than 3 counts.

⇒	If greater than the specified range, test the signal circuit terminal 2 for a short to ground. If the circuit tests normal, replace the HVAC control module.

5. Install a 3A fused jumper wire between the signal circuit terminal 2 and the low reference circuit terminal 1. Verify the appropriate scan tool actuator parameter is greater than 250 counts.

⇒	If less than the specified range, test the signal circuit for a short to voltage or an open/high resistance. If the circuit tests normal, replace the HVAC control module.

6. Connect a test lamp between control circuit A terminal 4 and control circuit B terminal 5.
7. Command the actuator in both directions with a scan tool. The test lamp should turn ON and OFF with each command.

⇒	If the test lamp remains always ON or always OFF during either commands, test for an open, short to ground, or short to voltage on either control circuit. If the circuit tests normal, replace the HVAC control module.

8. If all circuits test normal, replace the mode actuator.

Repair Instructions

Perform the Diagnostic Repair Verification after completing the diagnostic procedure.