AU
B2AB4-1D

This DTC indicates the electric air conditioning compressor (E-Compressor) internal high-voltage drive circuit detected an abnormal overcurrent condition — Atto 3

Thermal Management System

This DTC indicates the electric air conditioning compressor (E-Compressor) internal high-voltage drive circuit detected an abnormal overcurrent condition.

Specifically, the compressor's built-in permanent magnet synchronous motor (PMSM) drive current exceeded the IGBT power module safety threshold (typically 30-50A, depending on the vehicle model).

This fault involves the compressor internal high-voltage inverter module, motor winding insulation condition, or an abnormal mechanical load.

The compressor control unit (ECU) triggers this fault when it detects, via the Hall current sensor, that the instantaneous phase current continuously exceeds the calibrated threshold (e.g., 60A/100ms or 80A/10ms).

This fault initiates an automatic compressor protective shutdown, affecting air conditioning cooling and battery thermal management functions.

In extreme cases, it may damage the high-voltage fuse or high-voltage wiring harness.

The B2AB4-1D fault code on the Atto 3 indicates an overcurrent fault inside the electric air conditioning compressor’s high-voltage drive circuit. Severity is medium because it can shut down cooling and affect battery thermal management. Common causes include a shorted compressor motor winding, poor insulation, or a failed IGBT power module. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1Inter-turn short circuit in the internal compressor motor winding or decreased phase-to-phase insulation resistance (below 20MΩ) causes abnormally high operating current, typically resulting from prolonged high-temperature operation or degraded refrigerant oil.
  • 2Compressor controller IGBT power module breakdown (such as Infineon or ST brand modules) causes upper and lower bridge arm shoot-through or phase-loss operation, triggering overcurrent protection.
  • 3Scroll plate mechanical binding or wear (commonly due to refrigerant contamination or poor lubrication), causing a sudden increase in motor load torque and a corresponding rise in drive current.
  • 4Abnormal refrigerant circulation (severe undercharge or overcharge) causes poor internal compressor lubrication or liquid slugging, resulting in increased mechanical resistance torque and current fluctuations.
  • 5Compressor control board (PCB) current sensing circuit fault (e.g., shunt resistor value drift or damaged operational amplifier chip), triggering a false overcurrent signal.
What To Do
  • 1
    High-voltage safety procedure: Perform the standard power-down procedure (OFF position → disconnect low-voltage battery negative terminal → remove service disconnect/MSD → wait 5 minutes → verify zero voltage). Ensure the high-voltage system voltage is below 60V.
  • 2
    In-depth DTC diagnosis: Use VDS2000 or Launch X431 to read all DTCs. Check for accompanying fault codes (e.g., B2AB349 temperature sensor fault, B2AB149 motor phase loss). Review the Fault Freeze Frame data for the compressor speed, current, and bus voltage recorded at the time of the fault.
  • 3
    Wiring harness and connector inspection: Check the compressor high-voltage wiring harness (HV+, HV-) insulation for damage, measure the high-voltage interlock loop (HVIL) continuity, and check the low-voltage control plug (12Pin or 8Pin) for backed-out pins, oxidation, or signs of water ingress.
  • 4
    Insulation resistance and winding inspection: Use a 1000V megohmmeter to measure the insulation resistance between the compressor high-voltage terminal and the housing (must be >500MΩ). Use a micro-ohmmeter to measure the DC resistance of the three-phase windings (resistance deviation between UV/VW/WU must be <5%, approximately 0.5-2Ω at room temperature).
  • 5
    Mechanical system inspection: Check air conditioning line pressures (normal high-pressure side: 1.2-1.6 MPa; low-pressure side: 0.15-0.25 MPa). Check the refrigerant flow state at the sight glass. If necessary, recover the refrigerant and inspect the refrigerant oil for black discoloration or metal shavings.
  • 6
    Component replacement and system reset: If diagnostics confirm an internal compressor fault, replace the electric compressor assembly (part numbers vary by model, e.g., BC28A or BC36 series) and the desiccant canister. Add the standard amount of POE68 or ND-OIL11 refrigerant oil, evacuate the system (hold -0.1MPa for 30 minutes), and charge R134a or R1234yf refrigerant to the nameplate capacity.
  • 7
    Function verification and handover: Clear the fault codes. Power on the vehicle and perform the compressor self-test (typical self-test current: 2-5A). Observe the A/C cooling performance. Monitor the actual compressor operating current during a road test (normal operating current: 5-25A, varies with speed). Verify the fault code does not return.
Real-World Cases
BYD DTC AI Analysis

2019 Qin Pro EV: Air conditioning suddenly stopped working while driving

✓
At 30,000 km, the air conditioning suddenly stopped cooling while driving and the dashboard displayed "Thermal Management System Fault". The VDS scan reported codes B2AB4-1D and B2AB349 (internal temperature sensor fault). The data stream showed the compressor current spiked to 85A immediately before the failure (rated maximum 45A). Disassembly revealed the scroll plates inside the compressor had worn due to oil starvation, causing excessive motor load that triggered overcurrent protection. Replaced the compressor assembly, flushed the air conditioning lines, and added 150ml POE refrigeration oil and 450g refrigerant. Fault resolved.
BYD DTC AI Analysis

Batch failure of A/C compressor IGBT modules in new Yuan Plus vehicles

✓
After sitting overnight, the air conditioning failed to start and set DTC B2AB4-1D. Compressor three-phase winding resistance measured normal (1.2Ω) and insulation resistance >1000MΩ, ruling out motor failure. Disconnected the compressor high-voltage harness; controller-side bus voltage measured normal (320V), but a 'pop' came from inside the controller at power-up. Disassembled the compressor controller (without disassembling the compressor unit) and found the IGBT module (part number FS820R08A6P2B) collector-emitter shorted due to breakdown. Replaced the compressor controller board (BYD part number HAEG-8103020), clearing the fault.
Original source ↗
BYD DTC AI Analysis

Refrigerant leak caused compressor overcurrent in BYD Qin EV300

✓
Owner reported the A/C cooling gradually deteriorated until complete failure. Inspection found frost on the low-pressure line with abnormal pressures (low 0.05 MPa, high 0.8 MPa). Diagnosed as severe refrigerant leak. After recharging, the compressor ran for 5 minutes before setting DTC B2AB4-1D and shutting down. Prolonged operation with insufficient refrigerant caused inadequate internal lubrication; dry friction increased resistance in the scroll plates. Replaced the compressor and repaired the leak at the evaporator inlet pipe joint. Charged refrigerant and compressor oil to specification; system now operates normally.
Original source ↗
BYD DTC AI Analysis

Qin Pro DM compressor control board current sampling abnormality

✓
The vehicle intermittently sets DTC B2AB4-1D. When the fault occurs, the compressor immediately shuts down, but may operate normally after restarting. Monitored the compressor three-phase current waveforms with an oscilloscope and found high-frequency noise on the W-phase current sampling signal. Disassembled the compressor controller and found a dry solder joint on the current sampling resistor (0.005Ω/3W), causing the sampling voltage to drift and the ECU to falsely detect overcurrent. Resoldered the sampling resistor and applied conformal coating. The fault has not reoccurred.
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.