AU
B2AB41D

This fault code indicates the internal drive current of the thermal management system electric scroll compressor (E-Compressor) exceeds the safety threshold set by the MCU (microcontroller unit) (typically peak current >45A or sustained RMS current >15A) — Seal U

Thermal Management System

This fault code indicates the internal drive current of the thermal management system electric scroll compressor (E-Compressor) exceeds the safety threshold set by the MCU (microcontroller unit) (typically peak current >45A or sustained RMS current >15A).

This hardware-level protection fault indicates the compressor permanent magnet synchronous motor (PMSM) or its integrated controller (including the IPM intelligent power module) detects abnormal current consumption.

During compressor start-up or operation, the controller triggers this fault if Hall sensors detect a three-phase current imbalance exceeding 10%, or if the instantaneous DC bus current exceeds the calibrated limit (approximately 22-25A) for over 100ms.

The compressor stops immediately to protect the IGBT power devices, affecting cabin air conditioning cooling/heating and battery pack liquid cooling functions.

A prolonged fault may burn out the compressor controller or blow the high-voltage fuse (typically 30A-40A).

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Inter-turn short circuit or reduced phase-to-phase insulation (insulation resistance <20MΩ) in the electric compressor internal motor winding, causing an abnormal increase in electromagnetic load and a surge in operating current.
  • 2Compressor integrated controller fault, including IGBT breakdown in the IPM (Intelligent Power Module), current sampling resistor (shunt resistor) drift, or gate drive circuit malfunction causing three-phase drive waveform distortion.
  • 3Excessive mechanical load on the air conditioning system, such as refrigerant overcharge (exceeding the standard value of 550g±25g), blocked receiver-drier/expansion valve causing excessive high-side pressure (>2.5MPa), internal compressor mechanical seizure, or lack of compressor oil (POE oil) causing poor lubrication.
  • 4Abnormal high-voltage power supply circuit, including a burnt battery pack contactor causing a voltage drop (<320VDC), increased high-voltage wiring harness contact resistance (>10mΩ) causing voltage fluctuations, or EMC interference distorting the current sampling signal.
  • 5Thermal management control strategy or software calibration defects, such as start-up current ramp control failure, abnormal closed-loop speed PID parameters causing current surges, or refrigerant migration causing liquid slugging during sudden ambient temperature drops.
What To Do
  • 1
    Use the VDS2000/3000 diagnostic tool to read the complete fault codes and freeze frame data. Record the following key parameters at the time of the fault: compressor speed (rpm), high-voltage bus voltage (V), three-phase current values (A), refrigerant high- and low-side pressures (kPa), IGBT temperature (℃), and fault occurrence count (Trip Counter).
  • 2
    Perform the standard high-voltage power-down procedure (turn off the ignition switch, disconnect the low-voltage battery negative terminal, and wait 5 minutes). Wear CAT III 1000V insulated gloves. Use an insulation resistance tester to measure the insulation resistance between the compressor high-voltage input terminal and the vehicle body (standard: >500MΩ).
  • 3
    Check the air conditioning system static pressure (0.9-1.1 MPa at 25°C ambient temperature). Use a manifold gauge to check the dynamic pressures on the high and low sides (normal low pressure: 0.15-0.25 MPa; high pressure: 1.3-1.6 MPa). Confirm there is no ice blockage, debris blockage, or excessive refrigerant. Check the sight glass to confirm the refrigerant oil color and foam condition.
  • 4
    Disconnect the compressor low-voltage connector (usually 8-pin or 12-pin). Measure the DC resistance of the three-phase windings (U-V-W) using a micro-ohmmeter (standard value: 0.8-1.5Ω at 20°C) and calculate the three-phase imbalance (must be <5%). Measure the insulation resistance of each phase to the housing using a megohmmeter (must be >20MΩ).
  • 5
    Check the high-voltage interlock loop (HVIL) for continuity, measure the voltage drop across the high-voltage contactor contacts (should be <0.1V), verify proper grounding of the compressor high-voltage wiring harness shield, and confirm the supply voltage is within the 320-420VDC range with no severe fluctuations (ripple <5%).
  • 6
    If winding resistance is abnormal or insulation fails, replace the electric compressor assembly (part number may be BC-8103020E or similar). For refrigerant issues, recover the refrigerant using a recovery machine, replace the desiccant, evacuate the system to -0.1 MPa, and hold pressure for 15 minutes. Recharge with the standard amount (450-550 g, depending on the specific model) of R134a or R1234yf and the corresponding compressor oil (approx. 120-150 ml).
  • 7
    After replacement, perform the compressor self-learning procedure (if applicable). Use the diagnostic tool to run an active test to verify the compressor operates normally across the full speed range (1000-6000rpm), the current stabilizes within 3-12A, and there is no abnormal noise. Perform a 30-minute road test to verify the thermal management function and confirm the fault code does not return.
Real-World Cases
BYD DTC AI Analysis

Qin EV compressor winding insulation degradation causes intermittent overcurrent

✓
2019 BYD Qin EV, 68,000 km. Instrument cluster intermittently illuminated "Air Conditioning System Fault" warning. Retrieved DTC B2AB41D. Freeze frame showed compressor at 3,200 rpm drawing 18.5A (exceeding 15A calibration value) when fault occurred. Fault cleared after vehicle cooled while parked, but returned after 30 minutes of driving. Disassembly found compressor three-phase winding-to-housing insulation resistance was 50MΩ cold (normal) but dropped to 8MΩ at 60°C with heat gun (abnormal). Diagnosed as thermal degradation of enamelled wire insulation. Replaced electric compressor assembly, recovered and recharged refrigerant. Fault resolved.
BYD DTC AI Analysis

Ice blockage in refrigerant system triggered compressor overload protection

✓
2019 Qin EV. Heating worked normally in winter, but after 10 minutes of AC cooling, the system set DTC B2AB41D and the air conditioning stopped. Live data showed high-side pressure spiked instantly to 3.2 MPa (normal 1.5 MPa) before the fault, with current peaking at 26 A. Inspection revealed the receiver-drier had failed and system moisture was >500 ppm, causing ice blockage at the expansion valve. Recovered the refrigerant, replaced the receiver-drier and expansion valve, flushed the lines with nitrogen, evacuated and pressure-tested the system, then charged with the standard refrigerant amount and 30ml of fresh compressor oil. The fault has not returned.
BYD DTC AI Analysis

Burned high voltage contactor caused abnormal compressor current.

✓
After fast charging, DTC B2AB41D set along with the 'SRS fault' warning light. Diagnosis found the compressor controller detected excessive current fluctuation (ripple >5A). Measuring the HV line from the battery pack output to the compressor revealed burnt main positive contactor contacts with contact resistance of 15mΩ (normal <1mΩ). This dropped the voltage from 380V to 310V when the compressor started, causing the controller to pull abnormally high current to maintain power output. Replaced the battery pack main positive contactor (or the entire BDU - Battery Distribution Unit), cleaned the HV terminals, and resolved the fault.
BYD DTC AI Analysis

Drift in the compressor controller sampling resistor caused false fault reports.

✓
The vehicle had no actual air conditioning performance issues, yet the scan tool frequently logged historic DTC B2AB41D. Freeze frame showed only 12 A (below the actual threshold), but fault status read 'currently present'. Removed and inspected the compressor controller (did not disassemble the compressor body). Found a cold solder joint on the 5 mΩ precision shunt resistor in the current sampling circuit, causing sampling voltage drift. Resoldered the resistor and applied conformal coating, or calibrated the current sampling offset using an oscilloscope (wrote -0.8 A correction value via the scan tool). DTC cleared and did not recur.
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.