B3770 on GMC
Manufacturer-Specific Body Code (GM: Air Flow Control #6 / A/C Feedback Circuit Malfunction)
B3770 on GMC vehicles indicates manufacturer-specific body code (gm: air flow control #6 / a/c feedback circuit malfunction). Au7o has documented this code across 2 GMC models — most commonly on Sierra 1500, Sierra 3500HD. 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. Typical repair costs on GMC range from $150 to $700, depending on the specific model and root cause.
Common Causes of B3770
- •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
B3770 on GMC by Model
GMC Sierra 1500(1 issue)
- Blend Door / HVAC Actuator Failure Causing Clicking Behind Dash and Incorrect Air Temperature or Mode2000-2013
Sierra owners across both GMT800 and GMT900 generations frequently report small electric HVAC actuators stripping internal gears or losing calibration. The result is a repetitive clicking or tapping noise from the dash, air stuck on defrost or floor, or one side blowing hot while the other blows cold. This is one of the most common non-drivetrain complaints on these trucks and is heavily documented in owner forums and repair databases.
GMC Sierra 3500HD(1 issue)
- Blend door actuator failure causing temperature/airflow control problems2007-2019
Sierra 3500HD owners report clicking/ticking behind the dash and inability to control cabin temperature due to HVAC blend door or mode door actuator failures. GM service bulletins and owner reports describe stripped actuator gears or actuator motor failures that can leave the truck stuck on hot, cold, defrost, or a single vent mode.
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View B3770 across all makes →Frequently Asked Questions
What does B3770 mean on GMC?▼
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. On GMC specifically, this code is documented across 2 models.
What causes B3770 on GMC vehicles?▼
Common causes on GMC: 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. Specific causes vary by model and year — see the per-model sections below.
How much does it cost to fix B3770 on a GMC?▼
Repair costs on GMC range from $150 to $700, depending on the specific model and root cause.
Which GMC models have B3770 documented?▼
Au7o has documented B3770 on 2 GMC models: Sierra 1500, Sierra 3500HD.