AU
B2A4B92

This fault code indicates abnormal damper actuator position control within the air conditioning thermal management system — Seal U

Thermal Management System

This fault code indicates abnormal damper actuator position control within the air conditioning thermal management system.

Specifically, the recirculation door or blend door servo motor fails to reach the target position within the set time (typically 3-5 seconds), or the actual position feedback from the position sensor (generally a Hall effect sensor) deviates from the controller command by more than the threshold (typically >5%).

According to the control logic, the AC controller outputs a PWM signal to drive the motor while monitoring the sensor feedback voltage (0.5-4.5V range).

The controller triggers this code upon detecting a motor stall, step loss, sensor signal interruption, or abnormal voltage.

This fault disables fresh air/recirculation switching, delays cabin temperature adjustment, and causes abnormal demist mode operation.

In extreme cases, it affects battery pack cooling efficiency on vehicles utilizing an A/C refrigerant battery cooling architecture.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Worn or broken internal gear set in the recirculation flap actuator: The actuator uses plastic reduction gears. After long-term use, thermal expansion and contraction or dried grease causes the gears to slip or strip teeth. The motor spins freely, but the flap does not move.
  • 2Abnormal position sensor signal: Poor Hall sensor solder joints, magnetic ring displacement, or metal debris on the sensor surface causes an erratic or distorted feedback signal, leading the controller to incorrectly determine the motor failed to reach the target position.
  • 3Mechanical binding: Debris from worn air flap shaft bushing; improperly installed cabin air filter deforming and obstructing the air flap; evaporator case icing or foreign objects (such as leaves or small animals) jamming the air flap linkage mechanism.
  • 4Wiring harness connector fault: Water ingress or damp environments cause the cabin floor wiring harness actuator plug pins (usually 4-pin: power, ground, signal, feedback) to oxidize, back out, or increase contact resistance (>1Ω), resulting in insufficient drive current or signal attenuation.
  • 5Control strategy conflict: Outdated AC controller software loses initialization learned values in extreme temperatures (below -20°C or above 60°C), or failing to perform Door Position Learning after actuator replacement causes calibration deviation.
What To Do
  • 1
    Use the VDS2000 or VDS3100 diagnostic tool to read the freeze frame data. Record the ambient temperature, set temperature, and the difference between the motor target position and actual position when the fault occurred to confirm if the fault is intermittent. Clear the DTC, operate the fresh air/recirculation switch for 10 cycles, and observe if the fault reoccurs.
  • 2
    Remove the glove box or center console. Visually inspect the mounting condition of the recirculation flap actuator (typically a white or black plastic box-shaped component located above the blower). Inspect the wiring harness connector (BYD standard part number: KPB-4P-XXX) for green corrosion or looseness. Measure the supply voltage across connector pins 1-2 (should be 12V±0.5V with the key in the ON position). Measure the signal wire resistance to ground at pins 3-4 (should be >1MΩ).
  • 3
    Disconnect the actuator from the air flap linkage. Manually move the air flap blade to confirm no binding or abnormal noise throughout the full range of travel. If binding occurs, disassemble the evaporator housing to remove foreign objects. Check the air flap shaft bushing for wear (wear limit: radial clearance >0.5mm requires replacing the air flap assembly).
  • 4
    Measure the actuator motor resistance (normal value: 20-100Ω, varies by model). A resistance <10Ω or infinite indicates an internal short or open circuit. Apply 12V DC to test motor forward and reverse rotation, and listen to the gear meshing sound. If a slipping noise occurs, replace the actuator (part number reference: SC-8107020).
  • 5
    Use an oscilloscope to monitor the position feedback signal wire (Feedback). When operating the air flap, the waveform should change smoothly (0.5V-4.5V). If the signal drops out or changes abruptly, replace the actuator. After installing the new actuator, use the diagnostic tool to perform 'Air Flap Initialisation' (path: Air Conditioning System → Special Functions → Air Flap Position Learning) to recalibrate all air flap end positions.
  • 6
    Road test verification: Switch between different modes (recirculation/fresh air/demist) and verify the deviation between 'Recirculation Door Position Actual Value' and 'Target Value' in the data stream is <3% to confirm fault resolution.
Real-World Cases
BYD DTC AI Analysis

Recirculation flap gearset fracture caused fresh air/recirculation mode failure on Song MAX

✓
2018 BYD Song MAX DM, 62,000 km. Owner reported AC odor and poor cooling in summer. Scan tool logged DTC B2A4B92. Live data showed the flap position stuck at 15% (fresh air); the recirculation button did nothing. Disassembly revealed the recirculation flap actuator's final-stage gear (POM material) had stripped teeth. The motor spun but the flap did not move. Replaced the actuator assembly (Part No.: SC2E-8107020) and ran flap initialization. Live data then showed the position moving smoothly from 5% (recirculation) to 95% (fresh air). Fault resolved. Inspect the flap shaft for binding before replacement to avoid damaging the new gear.
BYD DTC AI Analysis

Oxidized wiring harness connector caused signal drift on the Qin EV

✓
2017 Qin EV300. After driving through water, the air conditioning temperature became uncontrollable and DTC B2A4B92 set. Inspection found water ingress at the passenger side floor harness connector (located near the air conditioning drain hose). The actuator signal pin (Pin 4) oxidised and blackened, with contact resistance at 12Ω (normal <0.5Ω). Cleaned the connector with precision electrical cleaner, applied conductive grease (Dow Corning DC-4), and sealed around the connector with adhesive. Signal voltage stabilised after the repair and the fault has not returned. Check floor harness sealing on vehicles that have been driven through water.
BYD DTC AI Analysis

Qin PRO DM: Evaporator icing jamming the air door

✓
2019 Qin PRO DM. Dashboard reported thermal management system fault when using the heater in winter. Retrieved DTCs B2A4B92 and B2A4B14 (history codes). Found the AC evaporator housing drain blocked, causing water to pool and freeze inside. Expanding ice jammed the recirculation air door linkage, stalling the actuator motor and triggering the fault. Cleared the drain hole and removed the ice. Checked expansion valve opening (to prevent evaporator temperature dropping too low). Sprayed silicone-based lubricant on the air door bushings. Root cause is a drain pipe design defect; recommend fitting a drain extension to prevent backflow.
BYD DTC AI Analysis

Replaced actuator without initializing it, causing the fault to persist.

✓
2019 BYD Song MAX. After installing a new recirculation flap actuator, DTC B2A4B92 remained. Found the technician had not performed flap position learning; the new actuator's zero position deviated approximately 40° from the controller's stored value. Used VDS3100 to enter 'AC System → Special Functions → Flap Position Learning' and followed the prompts: initialize all flaps to fully closed, then fully open, then return to default position. After learning completed, live data showed position error <1% and the DTC cleared. BYD models require initialization after actuator replacement. Otherwise, position deviation faults occur.
BYD DTC AI Analysis

Controller software defect causing false low-temperature warning

✓
2018 Qin Pro EV. During cold starts in -10°C winter conditions, the system set DTC B2A4B92; the fault cleared after warm-up. Freeze frame data showed actuator supply voltage at 11.8V (normal) when the fault triggered, but motor startup current reached 2.5A (normal 1.2A). Low temperatures thickened the grease, increasing starting resistance that the controller misread as a locked rotor. Solution: Flashed the AC controller to software version V2.3.1 (optimizing the motor drive PWM duty cycle and timeout logic for low-temperature operation), and replaced the grease with synthetic grease rated for low temperatures (Kluber Isoflex NBU 15). Cold starts are now 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.