AU
B2A2912

This fault code indicates abnormal continuity between the air conditioning system defrost flap actuator (Mode Actuator/Defrost Motor) drive circuit and the vehicle positive power supply (12V/B+) — Seal 6 EV

Thermal Management System

This fault code indicates abnormal continuity between the air conditioning system defrost flap actuator (Mode Actuator/Defrost Motor) drive circuit and the vehicle positive power supply (12V/B+).

In BYD new energy vehicles, the defrost motor is a stepper motor or DC servo motor that drives the mode flap inside the HVAC housing to switch between face, foot, defrost, and other air distribution modes.

When the air conditioning control module (ACU) or body control module (BCM) detects a short to power in this motor control circuit, it triggers DTC B2A2912 and enters protection mode.

The module stops drive output to the motor to prevent control chip burnout or wiring harness fires.

This fault disables the front windshield defrost function, severely compromising driving visibility and safety in low-temperature or high-humidity environments.

Secondary risks include blown air conditioning system fuses or control module overheating.

The B2A2912 fault code on the Seal 6 EV indicates a short to 12V power in the air conditioning defrost flap actuator drive circuit. This is a high-severity fault because it can disable front windshield defrosting and affect visibility. Common causes include a damaged actuator motor or chafed dashboard wiring contacting a power wire. The recommended fix is inspection and repair by an authorised dealer. Typical repair cost data is available from recorded cases.
4
Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1Internal coil insulation damage in the defrost flap actuator causes a short circuit between the positive and negative terminals, or a seized motor bearing causes an abnormal current increase that the system misinterprets as a short circuit.
  • 2The wiring harness under the dashboard chafes against a sharp metal body edge, damaging the insulation and causing the motor drive wire to contact a constant power wire (such as the instrument panel fuse box supply wire).
  • 3Condensation leakage or water ingress causes a short circuit between terminals in the connector near the air conditioning evaporator housing (usually a 4-pin or 6-pin white plug), especially between PIN1 (power supply) and PIN3 (motor drive).
  • 4Improper wiring harness routing during previous dashboard removal and installation allowed a screw to crush the harness, or a power wire accidentally punctured the air conditioning wiring harness during the installation of a dashcam or other aftermarket equipment.
  • 5The internal motor drive chip (usually an H-bridge driver IC) in the air conditioning control module (ACU) breaks down, causing the output terminal to continuously output a high level.
What To Do
  • 1
    Use the BYD dedicated diagnostic tool (VDS2000 or Launch X431) to read all DTCs and freeze frame data. Verify the ambient temperature, motor duty cycle, and other parameters at the time of the fault. Attempt to clear the fault code and observe if it immediately returns.
  • 2
    Check the air conditioning system fuses in the engine compartment and instrument panel fuse boxes (usually F1/10, F2/13, or 15A/20A fuses marked HVAC). Replace any blown fuse with one of the same rating. Never install a higher-rated fuse.
  • 3
    Remove the glove box or center console to expose the HVAC assembly. Locate the defrost mode door actuator (usually on the right side of the evaporator case, with a white plastic linkage) and disconnect its electrical connector.
  • 4
    Measure the actuator-side connector using a multimeter set to resistance. The defrost motor coil resistance should be 50-150 Ω (the stepper motor two-phase windings are approximately 100 Ω). A reading close to 0 Ω or less than 10 Ω indicates an internal short circuit in the actuator. Replace the actuator assembly (part numbers usually start with BC or EA).
  • 5
    If the actuator is normal, leave the actuator connector disconnected and measure the continuity of the control wire at the harness-side connector to body ground and the constant power supply (B+). The control wire must show no continuity to ground or power (infinite resistance). If the wire shows continuity to power, inspect the wiring harness along the circuit for damage.
  • 6
    Inspect the wiring harness protective sleeve for damage at the instrument panel crossmember retaining bolt, the evaporator housing edge, and near ground point G101 or G102 connecting to the front compartment wiring harness. Repair any damage and apply double protection using insulating tape and corrugated conduit.
  • 7
    Reconnect all connectors, clear the fault code, and perform the air conditioning system self-learning procedure (navigate to Special Functions → Air Flap Self-learning on the diagnostic tool). Verify smooth switching to defrost mode and check if the fault code returns.
Real-World Cases
BYD DTC AI Analysis

2018 BYD Song MAX: Defrost mode inoperative with blown fuse

✓
The customer reported that after activating front defrost mode, the AC panel displayed abnormally and the defrost function then failed completely. The technician used VDS to read DTC B2A2912 and found the instrument panel fuse box F1/10 (10A) blown. The replacement fuse blew again instantly. The technician disconnected the passenger side footwell trim panel and found the defrost damper actuator (part number BC-8112300) connector wiring harness cut by the sharp edge of the dashboard mounting bracket. The purple (motor drive +) and red (constant 12V) wires had damaged insulation that contacted each other, creating a short. The technician repaired the wiring insulation, added a rubber protective sleeve, and replaced the actuator (internally damaged by overcurrent). Fault resolved.
BYD DTC AI Analysis

2019 Qin EV: Unable to switch air conditioning modes after water ingress

✓
After driving through heavy rain and standing water, the instrument cluster displayed "Air Conditioning System Fault" and the defrost button did not respond. The scan tool retrieved codes B2A2912 and B2A2914 (defrost motor short to ground) present. Inspection of the lower HVAC assembly connector found obvious water traces with green oxidation on the pins. Disassembly showed the defrost actuator had an enclosed waterproof design and was undamaged, but the connector seal had deteriorated, allowing water entry and causing a short between the power and signal pins. Cleaned the connector with electrical contact cleaner, dried the wiring harness, replaced the waterproof seal and actuator connector. Fault resolved. Check the scuttle panel drain holes for blockages.
BYD DTC AI Analysis

Qin EV300: Sudden climate control failure following aftermarket modification

✓
After installing a 360-degree surround-view camera at an external modification shop, the customer found the AC only blew to the face vents and would not switch to defrost mode the next day, with a slight burning smell. Scanning showed DTC B2A2912. Inspection revealed the installer had driven self-tapping screws into the dashboard to secure the wiring harness; one screw pierced the defrost motor harness (yellow-green wire), shorting it to constant power. The damaged section sat behind the evaporator housing in a tight space. Technicians cut out the damaged length, soldered in replacement wire of the same gauge, insulated the splice with heat-shrink tubing, and rerouted the harness away from the screw holes.
BYD DTC AI Analysis

2019 Song MAX HVAC control module internal fault

✓
No external damage or water wading history. Demist function failed intermittently with DTC B2A2912. Previous repairs replaced the demist actuator and wiring harness without success. Detailed inspection found the fault only occurred with AC cooling on and ambient temperature above 35°C. Actuator circuit measurements normal. Diagnosis: AC control module (ACU, passenger side dashboard, PN 5A-8111030) internal H-bridge driver chip has poor thermal stability; high temperatures caused breakdown and output short to power. Replaced the AC control module and performed online programming via BYD Di-Link authorised account. Fault completely resolved.
Other Seal 6 EV 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.B1737DTC B1737 indicates the Supplemental Restraint System (SRS) detected abnormal continuity between the right middle-row side airbag squib circuit (typically the second-row right seat side airbag or right curtain airbag) and the vehicle power supply (B+, battery positive). The SRS ECU monitors the airbag inflator resistance via an internal current source (normal resistance: 2.0–3.0 Ω). If the ECU detects the voltage across the inflator circuit remaining close to battery voltage (>5 V and approaching 12 V) instead of the expected low potential or floating state, it identifies a short to power. This fault prevents the airbag from deploying normally during a collision because the short circuit bypasses the firing current. In extreme cases, abnormal current can cause unintended deployment, posing a severe safety hazard.B173BDTC B173B indicates an abnormal electric A/C compressor speed feedback signal or a communication fault between the compressor controller and the motor. In BYD new energy models (e.g., Tang, Song, Qin, and Yuan series), this DTC belongs to the HVAC subsystem within the Body Control system and specifically involves the electric compressor closed-loop control circuit. The ECU sets this DTC when the compressor controller (IPM) fails to receive a valid pulse signal from the Hall speed sensor for more than 3 continuous seconds, or when the deviation between the detected actual speed and the target commanded speed exceeds the calibrated threshold (typically >500 rpm). This fault forces the A/C system into fail-safe mode and stops compressor operation. Symptoms include a complete lack of cooling, intermittent cooling, or a sharp decrease in cooling performance. The instrument cluster A/C warning lamp may also illuminate. Prolonged operation with this fault can degrade high-voltage system insulation or cause controller overcurrent damage.
Common problems reported for Seal 6 EV →Seal 6 EV 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.