B3770: Manufacturer-Specific Body Code (GM: Air Flow Control #6 / A/C Feedback Circuit Malfunction)
2 vehicles · 1 makes · $150-$700 repair
Most Reported On
B3770 is an OBD-II diagnostic trouble code meaning “Manufacturer-Specific Body Code (GM: Air Flow Control #6 / A/C Feedback Circuit Malfunction).” B3770 is a manufacturer-specific body code. On GM vehicles it generally refers to an HVAC air-flow (mode/blend) control actuator feedback circuit malfunction, meaning the climate control module commanded a door actuator but received an out-of-range or no feedback signal. This typically results in air coming from the wrong vents or temperature/mode controls not working correctly. It is a comfort-system fault rather than a safety concern, and the exact channel should be confirmed for the specific vehicle. This code is most commonly reported on 2007-2019 GMC Sierra 3500HD, and 2000-2013 GMC Sierra 1500, with repair costs ranging from $150 to $700.
Common Causes
Typical Repair Cost
Based on 2 documented vehicle-specific issues. Actual cost depends on root cause and vehicle.
Diagnostic Tools
To diagnose B3770, you'll need an OBD-II scanner. Here are our recommendations at every price point.
ANCEL AD310 Classic OBD-II Scanner
by ANCEL
A simple, affordable code reader that reads and clears check engine codes. Great for quick diagnostics on any OBD-II vehicle (1996+).
- Read & clear engine codes
- View freeze frame data
- I/M readiness status
- No batteries or app needed
BlueDriver Pro Bluetooth Scanner
by BlueDriver
Bluetooth OBD-II scanner with a free companion app. Provides enhanced diagnostics, smog readiness, and repair reports sourced from a database of verified fixes.
- Enhanced diagnostics (ABS, SRS, transmission)
- Repair Reports with verified fixes
- Smog check readiness
- Free app (iOS & Android)
LAUNCH CRP123X OBD-II Scanner
by LAUNCH
A professional-grade handheld scanner that reads all four major systems (engine, transmission, ABS, SRS) with live data streaming and graphing.
- Engine, transmission, ABS, SRS diagnostics
- Live data stream & graphing
- AutoVIN for vehicle identification
- Free lifetime updates via Wi-Fi
Autel MaxiCOM MK808S Diagnostic Tool
by Autel
Shop-level diagnostic tablet with bi-directional control, active tests, and full system coverage. Ideal for serious DIYers and small shops.
- All-system diagnostics (25+ modules)
- Bi-directional control & active tests
- Oil reset, EPB, BMS, TPMS, injector coding
- 7-inch touchscreen with Android OS
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Vehicles Affected (2)
FAQ
What does B3770 mean?
B3770 stands for "Manufacturer-Specific Body Code (GM: Air Flow Control #6 / A/C Feedback Circuit Malfunction)." B3770 is a manufacturer-specific body code. On GM vehicles it generally refers to an HVAC air-flow (mode/blend) control actuator feedback circuit malfunction, meaning the climate control module commanded a door actuator but received an out-of-range or no feedback signal. This typically results in air coming from the wrong vents or temperature/mode controls not working correctly. It is a comfort-system fault rather than a safety concern, and the exact channel should be confirmed for the specific vehicle.
What are the most common causes of B3770?
The most common causes of B3770 are: Faulty HVAC mode/blend door actuator, Wiring or connector fault in the actuator feedback circuit, Stuck or broken air-distribution door, Short to voltage or ground in the circuit, HVAC/climate control module fault, Poor ground or low supply voltage. The specific cause varies by vehicle.
How much does it cost to fix B3770?
Repair costs for B3770 range from $150 to $700, depending on the vehicle and root cause.
Which vehicles are affected by B3770?
Au7o has documented B3770 across 2 vehicle models from 1 manufacturers: GMC.
Content compiled with AI assistance using NHTSA complaints, TSBs, and owner reports. May contain errors. Always verify with your vehicle's service manual.