AU
B2A2992

This DTC indicates the HVAC Defrost Mode Actuator fails to reach the control module's commanded target position within the specified time — Atto 3

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.

The B2A2992 fault code on the Atto 3 indicates the HVAC defrost mode actuator is not reaching the position requested by the control module in time. Severity is medium, as poor defrost operation can reduce windshield visibility. Common causes include jammed or broken actuator gears, a weak motor, or a stuck defrost flap/linkage. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
5
Cases Logged
5
Causes
Likely Causes — Atto 3
  • 1Jammed internal gears in the defrost flap actuator, broken plastic gear teeth, or worn motor carbon brushes cause insufficient driving force.
  • 2Deformed air flap shaft inside the HVAC housing, broken or detached plastic linkage, or foreign objects (such as leaves, foam particles, or paper labels) jamming the flap.
  • 3Poor contact or wear in the position sensor (potentiometer) causing an erratic signal, or a short or open circuit in the sensor power supply or signal circuit.
  • 4Actuator wiring harness connector poor connection, backed-out terminals, or oxidized/corroded pins; or unsecured harness after dashboard removal and installation causing chafing and an open circuit.
  • 5HVAC control module internal drive circuit fault, software logic error, or loss of air flap position learning data (common after power disconnection 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. Verify the data for other air doors (mode motor, fresh/recirculation motor) is normal to rule out a bus fault.
  • 2
    Operate the A/C panel to cycle through the defrost/face/foot modes. Listen for a clicking or continuous abnormal buzzing noise inside the dashboard to determine if the motor attempts to operate but is jammed.
  • 3
    Remove the front passenger glove box or lower dashboard trim panel. Visually inspect the defrost actuator (usually located on the right or top of the HVAC housing) to verify its installation condition and linkage connection, and check if the air flap shaft is broken.
  • 4
    Disconnect the actuator connector and measure the motor winding resistance (normal value approximately 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 recession.
  • 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 Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.
Common problems reported for Atto 3 →Atto 3 overview →
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.