AutoCodes – Generic – B3747

B3747 Code - Air Flow Control 1 Feedback Circuit

Quick Answer

The Heating, Ventilation, and Air Conditioning (HVAC) Control Module controls the HVAC actuators to regulate the airflow and temperature through the HVAC system. Common causes include Faulty Defrost Actuator, Defrost Actuator harness is open or shorted, Defrost Actuator circuit poor electrical connection. Severity is High - diagnose this code as soon as possible. Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

What it means: B3747 indicates Air Flow Control 1 Feedback Circuit.
Common causes: Common causes include Faulty Defrost Actuator, Defrost Actuator harness is open or shorted, Defrost Actuator circuit poor electrical connection.
Severity: High - diagnose this code as soon as possible.
Can I drive?: Driving is not recommended if the warning light is flashing, the engine runs poorly, or safety-related symptoms are present.

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Code Popularity 617

How popular is this code, among other codes? Low

Repair Importance Level

Urgent (Diagnose now) (3 / 3)

Repair Difficulty Level

Advanced (Pro) (3 / 3)

What is this?

Table of contents Created and updated by William Orellana on Mar 15, 2020

Description
Possible Causes
How To Fix
Cost to Diagnose
FAQs
Comments
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Code B3747 Description

The Heating, Ventilation, and Air Conditioning (HVAC) Control Module controls the HVAC actuators to regulate the airflow and temperature through the HVAC system. The actuators are 2 wire, bi-directional electric motors that share the same common control circuit. When the operator adjusts the actuators, the control module can only operate one actuator at a time due to the shared common control circuit. The control circuits use either a 0 or 12-volt value to co-ordinate the actuator movement. The HVAC control module reverses the polarity of the control circuits to move the actuator in the opposite direction.
The HVAC control module determines the door position by counting motor pulses on one of the control circuits. The HVAC control module converts the pulses to counts with a range of 0-255 counts.
When a calibration or recalibration procedure is performed, the HVAC control module calculates the door travel range. The HVAC control module compares the total number of pulses to calibrated limits. If the total pulse count is less than or equal to the maximum calibrated limited and more that or equal to the minimum calibrated limit, then the calibration is considered successful.

OBDII Code B3747 - Air Flow Control 1 Feedback Circuit - AutoCodes.com — B3747 Code - Air Flow Control 1 Feedback Circuit

What does this mean?

What are the Possible Causes of the DTC B3747?

Faulty Defrost Actuator
Defrost Actuator harness is open or shorted
Defrost Actuator circuit poor electrical connection
Faulty Heating, Ventilation, and Air Conditioning (HVAC) Control Module

How to Fix the DTC B3747?

Review the 'Possible Causes' above and visually examine the corresponding wiring harness and connectors. Check for damaged components and inspect connector pins for signs of being broken, bent, pushed out, or corroded.

What is the Cost to Diagnose the Code?

Labor: 1.0

To diagnose the B3747 code, it typically requires 1.0 hour of labor. Rates vary by location, vehicle, and shop. Many shops charge between $80–$150 per hour; dealerships and metro areas may be higher, independents may be lower.

Need more information about the B3747 code?

Need more information on how to fix the B3747 code? Get Access to Factory Service Manuals

Need Help with the Code?

Get the B3747 code diagnosed by a professional: Find a repair shop in your area

Information for Specific Makes

B3747 Buick — Air Flow Control 1 Feedback Circuit
B3747 Cadillac — Air Flow Control 1 Feedback Circuit
B3747 Chevrolet — Air Flow Control 1 Feedback Circuit
B3747 GMC — Air Flow Control 1 Feedback Circuit

About the author: William Orellana is a Master Mechanic and Mechanical Engineer with over 30 years of experience diagnosing and repairing vehicles. Learn more about his background.

Frequently Asked Questions about B3747 Code

1. What does the OBDII code B3747 mean?

The code B3747 indicates an issue with the Air Flow Control 1 Feedback Circuit, which monitors and adjusts airflow in the vehicle's HVAC system.

2. What are the common symptoms of the B3747 code?

Symptoms may include inconsistent or no airflow from vents, inability to adjust airflow direction, and an HVAC system that doesnâ€™t respond to controls.

3. What causes the B3747 code?

Common causes include a faulty air mix actuator, damaged wiring or connectors in the feedback circuit, or a malfunctioning HVAC control module.

4. Can I drive my car with the B3747 code active?

Yes, you can drive with this code active, but you may experience discomfort due to improper HVAC operation.

5. How is the B3747 code diagnosed?

A technician will inspect the air flow control actuator, check for damaged wiring, and use a scan tool to monitor the HVAC systemâ€™s feedback signals.

6. How do you fix the B3747 code?

Repairs typically involve replacing the faulty air mix actuator, repairing damaged wiring, or reprogramming or replacing the HVAC control module.

7. How much does it cost to fix the B3747 code?

Repair costs vary but typically range from $150 to $500, depending on the specific component that needs replacement or repair.

8. Can the B3747 code clear itself?

No, this code will not clear itself. The underlying issue must be resolved, and the code cleared with a scan tool.

9. What tools are needed to troubleshoot the B3747 code?

Youâ€™ll need an OBDII scanner, a multimeter to check electrical connections, and possibly a wiring diagram for the HVAC system.

10. Can a weak battery cause the B3747 code?

While rare, a weak or failing battery can sometimes cause electrical issues, including feedback circuit errors. Itâ€™s worth checking the battery voltage as part of diagnostics.