AU
B2A2914

DTC B2A2914 indicates a short to ground or open circuit in the HVAC Defrost Door Actuator drive circuit — Atto 3

Thermal Management System

DTC B2A2914 indicates a short to ground or open circuit in the HVAC Defrost Door Actuator drive circuit.

The air conditioning control module (ACECU) controls this actuator via a PWM signal or LIN bus to switch the door to the front windshield defrost mode.

The "14" in the fault code indicates the ECU detects abnormal circuit current: excessive current (short to ground) or zero/extremely low current (open circuit).

This fault disables the front windshield defrost function, causing glass fogging in low-temperature, high-humidity environments and severely impairing driving visibility and safety.

Additionally, due to the integrated logic between the thermal management and air conditioning systems, this fault may trigger a thermal management safety protection strategy, limit air conditioning compressor power, or illuminate the relevant high-temperature warning light.

3
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Internal motor coil of the defrost air flap actuator burned out or shorted to ground, causing abnormal resistance (normal: 20-80 Ω; near 0 Ω during a short circuit; infinite during an open circuit).
  • 2Worn or pinched wiring harness under the dashboard shorts the power or signal wire to body ground, or vibration breaks the wire, creating an open circuit.
  • 3Actuator connector pins (usually located on the right side of the HVAC assembly, near the blower) oxidized, backed out, or corroded by water ingress, causing excessive contact resistance or a complete open circuit.
  • 4Internal MOSFET driver chip in the air conditioning control module (ACECU) damaged, failing to output normal drive voltage or misinterpreting the current sampling value.
  • 5Mechanical binding of the defrost flap (e.g., deformed linkage or foreign object blocking the flap hinge) causes a motor stall current spike, triggering overcurrent protection and logging a short circuit fault.
What To Do
  • 1
    Use a VDS2000 or Launch X431 diagnostic tool to read all fault codes. Check for accompanying faults such as B2A2912 (short to power) or B2A2992 (target position not reached). Record the ambient temperature and air flap position from the freeze frame data.
  • 2
    Remove the trim panel below the passenger-side dashboard and locate the defrost actuator (usually a white or black plastic box-shaped component with a 4-pin or 5-pin connector). Inspect the connector for looseness, water ingress, or obvious burn marks. Clean the terminals with electrical contact cleaner.
  • 3
    Disconnect the actuator connector and use a multimeter to measure the resistance between the motor-side pins (Song MAX/Qin EV standard value: approx. 25-35 Ω). Resistance <5 Ω indicates an internal short circuit, and infinite resistance indicates an internal open circuit. Replace the actuator assembly (typical part number HA-8112200-C1).
  • 4
    Measure the harness-side connector: resistance to ground must be >10MΩ (to rule out short to ground) and voltage to ground must be 0V (to rule out short to power). If abnormal, trace the circuit and inspect the harness for wear at the firewall pass-through and instrument panel frame mounting points.
  • 5
    Use the diagnostic tool to perform the 'Air Flap Active Test' and select 'Defrost Mode'. Simultaneously use an oscilloscope or multimeter to measure the voltage change at the control module output terminal (voltage should toggle between 0-12V or display a LIN bus waveform). If there is no output, the ACECU is faulty.
  • 6
    Check the air flap mechanical linkage for detachment or binding. Manually move the air flap; it should move smoothly without resistance. If mechanical binding exists, disassemble and repair the HVAC assembly to prevent damaging the new actuator.
  • 7
    After replacing the actuator, use the diagnostic tool to perform 'Air Door Position Learning' or 'A/C System Initialisation' (required on some models). Clear the fault code and repeatedly test switching between defrost/face/foot modes. Confirm in the data stream that the error between the 'Defrost Air Door Actual Position' and the 'Target Position' is <5%.
Real-World Cases
BYD DTC AI Analysis

2018 Song MAX: Defrost mode inoperative with burning smell

✓
The instrument cluster displayed DTC B2A2914 on arrival. The owner reported the front windscreen would not demist. Inspection revealed burn marks on the defrost actuator connector at the right side of the HVAC assembly. Disassembly showed the internal gears seized and the motor coil burned out from overheating, causing a short to ground. Replaced the defrost actuator, cleaned the air door tracks, and performed air door position learning. Fault resolved. The owner stated the cabin filter had been replaced at an external repair shop; improper procedure likely allowed foreign objects to enter the air duct, causing the seizure.
BYD DTC AI Analysis

2019 Qin EV: Intermittent Defrost Motor Open Circuit

✓
Intermittent DTCs. Air-conditioning mode auto-switched while driving. Inspection found dashboard frame mounting screws crushing the wiring, nearly severing the ground wire in the defrost-motor harness—only a few copper strands remained. Vehicle vibration caused intermittent open circuit. Rerouted wiring to avoid sharp frame edges, soldered the break and applied heat-shrink tubing. Fault resolved. Also found an aftermarket dashcam with wiring interfering with the original air-conditioning harness; corrected.
BYD DTC AI Analysis

Song MAX DM multiple air damper faults after water ingress including B2A2914

✓
Vehicle submerged to dashboard height. After repair, the climate control system logged multiple air door faults (defrost, footwell, and recirculation). Disassembly revealed sediment inside the defrost actuator connector; reduced insulation resistance between the pins caused a short to ground. Cleaned all actuator and ACECU connectors with anhydrous alcohol, dried the HVAC assembly for 48 hours, applied insulating silicone grease, and reassembled. Cleared the fault codes and restored all air doors to normal operation, avoiding a costly ACECU replacement.
Other Atto 3 Fault Codes
P0A0DBattery Energy Control Module Requested MIL IlluminationP0AA6Hybrid Battery Voltage System Isolation FaultP1A00Drive Motor "A" Performance — BYD proprietaryB1108For the BYD Song MAX (2017–2019), DTC B1108 indicates a short circuit in the PM2.5 air quality detection module (dust sensor) or its wiring harness. The sensor uses laser scattering to detect in-cabin and outside PM2.5 concentrations and transmits data to the HVAC ECU via the LIN bus or an analog signal. Short circuit conditions include: 1) Sensor power supply wire (+5V/+12V) shorted to ground 2) Signal wire shorted to power or ground 3) Short circuit in the sensor's internal photoelectric detection circuit This fault prevents the automatic climate control from switching between fresh air and recirculation based on air quality. The system enters fail-safe mode (typically forced recirculation). Severe short-circuit current can destroy the HVAC ECU sampling circuit. The system classifies this as a Level 3 severe fault and restricts vehicle operation to prevent electrical fires or controller damage. For other BYD models (such as the Qin EV, E5, and Song DM), B1108 indicates a driver-side sunload sensor fault, reflecting differences in DTC definitions across models.B110811This DTC indicates a short circuit in the air conditioning system PM2.5 air quality sensor (rapid detector). Specifically, abnormal continuity exists between the sensor power supply circuit or signal output circuit and body ground or battery positive. This causes the control module (ACU/air conditioning controller) to detect abnormal current or a voltage signal outside the valid range (typically 0V or supply voltage). The PM2.5 sensor monitors internal and external particulate concentrations, providing the data the automatic air conditioning system uses to switch between fresh air and recirculation modes. A short circuit disables the air quality monitoring function. This fault may force the air conditioning system into recirculation protection mode and trigger related thermal management system faults, as the air conditioning system acts as a key actuator in vehicle thermal management. In severe cases, the short circuit current can damage the internal sampling circuit of the air conditioning controller or overheat the wiring harness.
Data confidence: Official This information is for reference only. Always consult a qualified technician for diagnosis and repair. Do not attempt high-voltage system repairs yourself.