AU
B2A2914

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

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 — Seal U
  • 1Defrost flap actuator internal motor coil burned out or shorted to ground, causing abnormal resistance (normally 20-80 Ω; near 0 Ω when shorted; infinite when open).
  • 2A worn or pinched wiring harness under the dashboard shorts the power or signal wire to body ground, or vibration breaks the wire, resulting in an open circuit.
  • 3Oxidation, pin back-out, or water ingress corrosion at the actuator connector (usually located on the right side of the HVAC assembly, near the blower), causing excessive contact resistance or a complete open circuit.
  • 4A damaged MOSFET driver chip inside the air conditioning control module (ACECU) fails to output normal drive voltage or misinterprets the current sampling value.
  • 5A jammed defrost flap mechanism (e.g., deformed linkage or foreign object obstructing the flap hinge) causes motor stall current to surge, triggering overcurrent protection and setting 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 (failed to reach position). Record the ambient temperature and air flap position from the freeze frame data.
  • 2
    Remove the trim panel under the passenger-side dashboard and locate the defrost actuator (usually a white or black plastic box-shaped component with a 4-wire or 5-wire connector). Check the connector for looseness, water ingress, or obvious burn marks. Clean the pins with electrical contact cleaner.
  • 3
    Disconnect the actuator connector. 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. Infinite resistance indicates an internal open circuit. If either condition exists, 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 a short to ground), and voltage to ground must be 0V (to rule out a short to power). If abnormal, trace the circuit and inspect the wiring harness for wear at the firewall pass-through hole 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 (the 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 disconnection or binding. Manually move the air flap; it must move smoothly without resistance. If binding occurs, disassemble and repair the HVAC assembly to prevent damage to 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, and foot modes. Verify in the data stream that the deviation between 'Defrost Air Door Actual Position' and '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 Seal U Fault Codes
B1108For 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.B1109DTC B1109 indicates an open circuit in the communication line between the air conditioning system PM2.5 air quality sensor (dust concentration sensor) and the air conditioning control unit (AC ECU), or an open circuit within the sensor internal circuitry. Typically located in the air conditioning intake duct, this sensor monitors real-time PM2.5 particle concentration inside and outside the vehicle. It provides data to the automatic air conditioning system for intelligent switching between fresh air and recirculation modes and for controlling the air purification device. During an open circuit fault, the AC ECU cannot receive the air quality signal, triggering the system fail-safe mode. Symptoms typically include failure of the automatic recirculation function, abnormal air purification indicator light operation, or abnormal air quality data displayed on the air conditioning panel. Severe cases may compromise the cabin environment control strategy, but do not directly affect vehicle driving safety.B110913DTC B110913 indicates an open signal circuit for the PM2.5 rapid detector (in-cabin air quality sensor). This sensor typically mounts inside the air conditioning system intake duct. It monitors in-cabin PM2.5 concentration in real time and provides data to the automatic air conditioning system for intelligent control of the air purification function. The BYD diagnostic protocol uses sub-code '13' to specifically indicate an open signal circuit. Although this fault theoretically affects a comfort feature, BYD Qin series vehicles classify it as a Level 3 (severe) fault. This classification occurs because the air conditioning system interacts with the battery thermal management system (e.g., monitoring battery cooling intake air quality). The fault can disable the automatic air conditioning mode and prevent the air purification function from operating. In extreme cases, it affects the battery compartment intake air quality assessment, triggering the 'repair immediately' strategy.B110AThis DTC indicates interrupted CAN bus communication or abnormal data between the air conditioning control unit (ACU) and the PM2.5 air quality sensor. The PM2.5 sensor monitors particulate concentration inside and outside the vehicle and provides the basis for purification control in the automatic air conditioning system. The ACU triggers this fault if it fails to receive a valid CAN message from the sensor within the specified period (usually 100-500 ms), if message verification fails, or if the signal frame times out. Although this fault does not affect vehicle driving safety, it disables the automatic air purification function. The air conditioning system cannot automatically switch between recirculation and fresh air modes or activate the air purification mode based on air quality. A persistent fault may restrict the thermal management strategy.
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.