AU
B2A2992

This DTC indicates the HVAC Defrost Mode Actuator fails to reach the control module's commanded target position within the specified time — Seal U

Thermal Management System

This DTC indicates the HVAC Defrost Mode Actuator fails to reach the control module's commanded target position within the specified time.

The defrost motor, typically a stepper motor or DC gear motor with position feedback (potentiometer or Hall sensor), drives the mode door to engage the front windshield defrost mode.

After sending a position command, the HVAC control module continuously monitors the position sensor feedback voltage (typically a 0-5V analog signal or PWM signal).

The module triggers DTC B2A2992 if the deviation between the actual and target positions exceeds the threshold (e.g., 5%-10%) within the specified time (typically 10 seconds), or if it detects abnormal motor current (stall current).

This fault disables the defrost function or causes abnormal airflow distribution.

In low-temperature and high-humidity environments, the system fails to defog the front windshield, severely compromising driving safety.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Defrost flap actuator internal gears jammed, plastic gear teeth broken, or motor carbon brushes worn, causing insufficient driving force.
  • 2Air flap shaft inside the HVAC housing deformed, plastic linkage broken or detached, or foreign objects (such as leaves, foam particles, or label paper) jamming the air flap
  • 3Poor contact or wear in the position sensor (potentiometer) causing an erratic signal, or an open or short circuit in the sensor power supply or signal circuit.
  • 4Poor connection, backed-out terminal, or oxidized/corroded pins at the actuator wiring harness connector, or harness wear and open circuit resulting from an unsecured harness after dashboard removal and installation.
  • 5HVAC control module internal drive circuit fault, software logic error, or loss of air flap position learning data (common after power loss or module replacement without initialization).
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (ED400/VDS) to read the data stream. Compare the 'Defrost Air Door Target Position' and 'Actual Position' values to confirm the deviation. Simultaneously check the data of other air doors (mode motor, recirculation/fresh air motor) for normal operation to rule out a bus fault.
  • 2
    Operate the air conditioning panel to cycle through defrost/face/foot modes. Listen for abnormal clicking or continuous buzzing noises inside the dashboard to determine if the motor is attempting to operate but is jammed.
  • 3
    Remove the front passenger glovebox or lower dashboard trim panel. Visually inspect the defrost actuator (usually located on the right or top of the HVAC housing) for mounting condition, linkage connection, and a broken air flap shaft.
  • 4
    Disconnect the actuator connector. Measure the motor winding resistance (normal value approx. 20-100 Ω, depending on the specific model) and the position sensor resistance (must change smoothly as the gear rotates, with no jumps or open circuits). Inspect the connector pins for oxidation or pushback.
  • 5
    If mechanical components and wiring are normal, use the diagnostic tool to perform the 'Air Flap Position Learning' or 'A/C Initialization' procedure (on some models, select 'Special Functions' - 'Air Flap Calibration' via VDS). If learning fails or the fault recurs, replace the defrost air flap actuator assembly and perform position learning again.
Real-World Cases
BYD DTC AI Analysis

Song MAX broken defrost damper linkage causes sticking

✓
Symptoms: 2018 Song MAX — no airflow from vents when front defrost mode selected; clicking noise from inside the dashboard; DTC B2A2992 stored. Diagnosis: Removed the glove box to inspect the defrost actuator. Gears operated normally, but the white plastic linkage connecting to the flap had snapped, trapping the flap in the face-level vent position. Repair: Replaced the HVAC box flap linkage assembly (some models require the complete flap assembly), reconnected the actuator, and performed the flap position learning procedure. Fault cleared.
BYD DTC AI Analysis

Qin EV: Defrost actuator motor internal open circuit

✓
Symptom: 2019 Qin EV defrost function failed suddenly. No warning lamp, but historic DTC B2A2992 stored. Diagnosis: Supply voltage at the actuator connector measured 12V (normal). Motor winding resistance measured infinite (open circuit), confirming internal coil break. Disassembled the actuator; motor brushes were worn out. Repair: Replaced the defrost air door actuator (part number likely EQEA-8101810 or similar). After installation, ran 'HVAC flap initialization' using VDS; live data confirmed normal position tracking.
BYD DTC AI Analysis

Song MAX – Loose wiring connector causing intermittent fault

✓
Symptoms: 2017 Song MAX instrument cluster occasionally displayed air conditioning fault warning when driving on rough roads. Diagnostic tool retrieved intermittent fault code B2A2992. Diagnosis: Found broken locking tab on actuator connector and enlarged, loose pins. Position signal in data stream jumped when gently shaking wiring harness. Resolution: Repaired wiring harness connector (replaced connector or tightened pins), secured harness with cable ties to prevent rubbing against dashboard frame, cleared fault codes. No recurrence after one week of monitoring.
BYD DTC AI Analysis

BYD Qin EV300: AC not initialized after battery pack replacement

✓
Symptoms: 2017 BYD Qin EV300 set false DTCs B2A2992 and B2A2914 (defrost motor short to ground/open circuit) and the defrost mode wouldn't hold after the high-voltage battery pack was replaced and the 12V auxiliary battery disconnected. Diagnosis: Line checks found no shorts, the actuator tested normal, but the data stream showed position feedback voltage locked at 0V. Fix: Using the scan tool, navigate to Air Conditioning System > Special Functions > Air Door Position Learning and complete the limit position calibration for all air doors (defrost, mode, recirculation) as prompted. The DTCs cleared automatically and system operation returned to normal.
BYD DTC AI Analysis

Song MAX: Foreign object jamming air flap in HVAC unit

✓
Symptoms: The owner of a 2019 Song MAX reported weak airflow in defrost mode accompanied by a squeaking friction noise. DTC B2A2992 stored. Diagnosis: Removed the blower motor and found leaves lodged in the air outlet. Further disassembly of the HVAC box revealed a paper label jammed at the edge of the defrost damper, preventing full closure. Continuous actuator stall triggered the fault. Resolution: Cleared all foreign objects from the HVAC box. Checked the damper sealing sponge for detachment (replace if necessary). Reset the actuator and tested all modes for smooth switching.
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.