AU
B2AB4-1D

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

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.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1An inter-turn short circuit in the compressor internal motor winding or a drop in phase-to-phase insulation resistance (below 20MΩ) abnormally increases the operating current. Prolonged high-temperature operation or refrigerant oil deterioration usually causes this.
  • 2Compressor controller IGBT power module breakdown (e.g., Infineon or ST brand modules), causing shoot-through of the upper and lower bridge arms or phase-loss operation, triggering overcurrent protection.
  • 3Mechanical seizure or wear of the scroll plate (often due to refrigerant impurities or poor lubrication) causes 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, increasing mechanical resistance torque and current fluctuation.
  • 5Compressor control board (PCB) current sampling circuit fault (e.g., shunt resistor value drift or damaged operational amplifier chip), causing 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) to 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 (such as B2AB349 temperature sensor fault, B2AB149 motor phase loss). Review the Fault Freeze Frame data for the compressor speed, current value, and bus voltage recorded at the time of the fault.
  • 3
    Wiring harness and connector inspection: Inspect 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 connector (12Pin or 8Pin) for backed-out pins, oxidation, or water ingress.
  • 4
    Insulation resistance and winding test: 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 the A/C line pressure (normal high-pressure side: 1.2-1.6 MPa; low-pressure side: 0.15-0.25 MPa). Check the refrigerant flow at the sight glass. If necessary, recover the refrigerant and check if the compressor oil is black or contains metal shavings.
  • 6
    Component replacement and system reset: If diagnostics confirm an internal compressor fault, replace the electric compressor assembly (part number depends on vehicle 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 -0.1 MPa for 30 minutes), and charge R134a or R1234yf refrigerant to the amount specified on the nameplate.
  • 7
    Function verification and vehicle handover: Clear the fault code. Power on the vehicle and perform the compressor self-test (typical self-test current: 2-5A). Observe the A/C cooling performance. Road test the vehicle and monitor the actual compressor operating current (normal operating current: 5-25A, varying 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 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.