AU
B2A4B14

This DTC indicates a fault in the drive circuit of the HVAC Recirculation Air Door Actuator motor — Seal U

Thermal Management System

This DTC indicates a fault in the drive circuit of the HVAC Recirculation Air Door Actuator motor.

Specifically, a "short to ground" indicates insulation failure between the motor supply line (typically the PWM control line or power line) and the vehicle body ground (GND), causing abnormal current leakage.

An "open circuit" indicates a broken internal motor coil, a loose connector, or a severed wiring harness.

This motor switches the HVAC air door between fresh air and recirculation modes.

A fault prevents mode switching or causes the door to stick in a fixed position, reducing cabin temperature control efficiency.

In extreme cases, this reduces battery thermal management performance (e.g., preventing effective heat dissipation via fresh air mode).

Therefore, the system classifies this as a severe fault.

3
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Recirculation air flap actuator motor internal coil burnt out or short-circuited: Prolonged motor jamming or overload damages the coil insulation, causing a short to ground or internal open circuit.
  • 2Wiring harness and connector fault: Water ingress or poor sealing corrodes or oxidizes pins in the wiring harness connector near the HVAC unit (usually located behind the glove box or at the firewall), or vehicle vibration loosens the male and female terminals.
  • 3Motor damage due to mechanical jamming: Foreign objects (such as leaves or accumulated dust) jam the air flap mechanism, or the linkage mechanism deforms. The resulting excessive motor stall current eventually burns out the drive circuit or motor winding.
  • 4Air conditioning controller (HVAC ECU) internal fault: A damaged internal H-bridge drive circuit or MOSFET causes an abnormal output signal (such as a short to ground) and triggers a false fault.
  • 5Wiring harness worn or damaged: An improperly secured wiring harness in the engine compartment or instrument panel rubs against metal body edges, damaging the insulation and causing a short to ground.
What To Do
  • 1
    Diagnostic confirmation: Use the BYD VDS diagnostic tool to read all DTCs. Confirm if only B2A4B14 is present or if related fault codes exist. Record freeze frame data (such as motor duty cycle and position feedback values at the time of the fault). Clear the fault codes, operate the fresh air/recirculation switch, and confirm if the fault recurs.
  • 2
    Visual and connector inspection: Remove the glovebox or front passenger lower trim panel and locate the recirculation air flap actuator (usually marked 'REC' or 'Intake'). Check the connector for looseness, backed-out pins, or green/white corrosion. Measure the connector terminal resistance to ground to check for a short circuit.
  • 3
    Actuator unit inspection: Disconnect the connector and use a multimeter to measure the resistance between the two motor terminals (normal range is typically 30-80 Ω; refer to the vehicle repair manual for specifics). A resistance of 0 Ω indicates a short circuit; infinite resistance indicates an open circuit. Simultaneously, manually actuate the air flap to confirm the mechanism operates without binding or abnormal noise.
  • 4
    Harness continuity and insulation test: Measure harness continuity (power, ground, and signal wires) from the actuator connector along the harness toward the air conditioning controller. Use a megohmmeter or a multimeter on the high-resistance setting to measure the insulation resistance of each wire to ground. Resistance must be greater than 1 MΩ. Inspect harness bend points passing through the firewall and hinges.
  • 5
    Controller output check: Connect the diagnostic tool and perform an Actuation Test. Observe the air conditioning controller PWM output waveform and voltage to the recirculation motor. If the controller output is normal but the motor does not operate, replace the actuator. If the controller has no output or the output shorts to ground, repair or replace the air conditioning controller.
  • 6
    Component replacement and repair: Replace the recirculation air flap actuator motor (some models require replacing the complete air flap housing assembly), or repair the damaged wiring harness (seal with heat-shrink tubing and restore original wrapping). If the flap mechanism binds, clear foreign matter and apply specified grease.
  • 7
    Calibration and verification: After completing the repair, use VDS to run the 'Door Motor Calibration' procedure so the controller learns the air flap limit positions. Operate the recirculation/fresh air switch and confirm the air flap moves smoothly without abnormal noise. Read the data stream to confirm the position feedback value changes with the command (recirculation is typically 0-20%, fresh air is 80-100%). Road test the vehicle to verify the fault code does not recur.
Real-World Cases
BYD DTC AI Analysis

Song MAX recirculation door jammed, motor burned out

✓
A 2018 BYD Song MAX DM with 60,000 km displayed "Air Conditioning System Fault" on the dashboard. Found DTC B2A4B14. Disassembly revealed mud ingress at the recirculation door actuator connector and the door shaft jammed with accumulated leaves and dust. The motor continuously attempted to drive while stalled, overheating and burning out the internal coil. Measured resistance: 0.5Ω (short to ground). Solution: Cleaned the door mechanism and foreign objects from the HVAC unit, lubricated the shaft, replaced the recirculation door actuator, and cleaned and waterproofed the wiring harness connector. Fault resolved.
BYD DTC AI Analysis

Qin Pro EV HVAC unit wiring harness chafed, shorted to ground

✓
2019 BYD Qin Pro EV. Intermittent B2A4B14 DTC. When the fault occurred, the recirculation mode would not switch. Inspection revealed the fault occurred on rough roads. Removed the passenger side dashboard and found the recirculation flap actuator power supply wire (pink) had chafed against a metal body bracket where it passes through the firewall. Damaged insulation caused an intermittent short to earth. Measured resistance from the wire to earth with a multimeter; resistance fluctuated between 0–10 ohms when moving the harness. Repair: Cut out the damaged section, soldered in an extension, and insulated with double-layer heat shrink tubing. Re-secured the harness routing and added a rubber grommet to prevent chafing. Fault has not reoccurred.
BYD DTC AI Analysis

Qin EV300 Actuator Internal Open Circuit Fault

✓
2017 BYD Qin EV300. Air conditioning recirculation mode inoperative, system forced to fresh air mode with DTC B2A4B14 stored. Scan tool live data showed 'Invalid' for flap position. Measured motor coil resistance at the recirculation flap actuator connector: open circuit (infinite resistance). Disassembled the actuator: gearset intact, but motor brushes severely worn causing open circuit. This model uses a sealed, non-serviceable actuator. Replaced the air conditioning recirculation flap actuator assembly (part number similar to BG-8112600). Performed flap calibration after replacement. Recirculation and fresh air functions returned to normal.
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.