AU
B2AB0-49

DTC B2AB0-49 indicates an abnormality in the electric A/C compressor current sampling circuit — Seal U

Thermal Management System

DTC B2AB0-49 indicates an abnormality in the electric A/C compressor current sampling circuit.

In electric compressors driven by a three-phase permanent magnet synchronous motor (PMSM), the controller (MCU) monitors the motor phase currents (U/V/W phases) in real time via a Hall effect sensor or precision shunt resistor for field-oriented control (FOC) and overcurrent protection.

This fault indicates the sampling signal exceeds the valid threshold (open circuit, short circuit, or short to power/ground).

Consequently, the compressor controller cannot accurately read the motor current value and triggers a protection mechanism to stop the compressor, impairing A/C cooling and battery thermal management functions.

This is a hardware-level circuit fault, not a software logic error.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Damaged or degraded internal Hall current sensor in the electric compressor causing output signal drift or interruption.
  • 2Current sensing resistor (typically a milliohm precision resistor) on the compressor controller board (PCB) is burnt or has a cold solder joint.
  • 3Poor contact, terminal back-out, or corrosion from water ingress in the low-voltage signal wiring harness, causing abnormal transmission of the 5V reference voltage or sampling signal.
  • 4Damaged compressor high-voltage harness insulation interferes with the low-voltage sampling signal or causes overvoltage damage to the controller internal sampling circuit.
  • 5An inter-turn short circuit or insulation degradation in the compressor motor winding distorts the actual current waveform, triggering abnormal sampling protection.
What To Do
  • 1
    Use the VDS2000/VDS3000 diagnostic tool to read all fault codes, check for related faults such as B2AB049 and B2AC000, and record the freeze frame data.
  • 2
    Check the electric compressor low-voltage connector (usually located on the top or side of the compressor, 4-5 pins) for looseness, water ingress, or pin oxidation. Measure the connector terminal voltages to verify the power (+12V/+5V), ground (GND), and CAN lines (around 2.5V) are normal.
  • 3
    Disconnect the high-voltage service disconnect (MSD) and wait 5 minutes for the high-voltage capacitor to discharge. Measure the insulation resistance to ground of the compressor high-voltage harness positive and negative terminals. The resistance must be greater than 500 MΩ (use a 1000V megohmmeter).
  • 4
    Disconnect the compressor low-pressure connector and use an oscilloscope to check the current sampling signal waveform (if equipped with a Hall sensor, normal output is a 0.5-4.5V linear voltage or a PWM signal). If the signal is a constant 0V or 5V, confirm a sensor fault.
  • 5
    If the external wiring is normal but the fault persists, the compressor internal controller board is faulty. BYD electric compressors (such as Sanden Behr or Aotecar integrated compressors) come as complete assemblies; do not repair the controller board separately. Replace the entire electric compressor assembly. Recover the refrigerant, evacuate the system, and charge the standard amount of R134a (about 600-800g, depending on the vehicle model).
  • 6
    After replacement, use the diagnostic tool to perform 'A/C system self-learning' or 'compressor zero-point calibration' (required on some models). Clear the fault code and road test the vehicle. Observe the data stream to verify 'compressor speed' and 'compressor current' change normally when turning on the air conditioning.
Real-World Cases
BYD DTC AI Analysis

Qin PRO EV compressor Hall sensor intermittent open circuit

✓
The vehicle came in with intermittent A/C cooling failure and intermittent DTC B2AB0-49. Inspection found expanded pin sockets in the compressor low-voltage connector were interrupting Hall sensor power supply when the vehicle vibrated. Re-crimped the pins and applied conductive grease. Fault resolved. This case shows vibration-induced poor contact is a common cause.
BYD DTC AI Analysis

Qin EV300 compressor controller board sampling resistor burnt out

✓
Customer reported complete AC failure. Retrieved active DTC B2AB0-49. Disassembled compressor controller; internal sampling resistor (1mΩ precision resistor) burned out from high voltage surge, surface charred. Traced to previous use of non-standard charging station causing voltage fluctuation. Replaced electric compressor assembly; fault resolved.
BYD DTC AI Analysis

热管理线束磨损导致信号干扰

✓
车辆行驶中空调突然停止，仪表显示热管理系统故障。检查发现前舱左侧空调压缩机低压线束与车架干涉磨损，导致电流采样信号线（黄色）对地短路。修复线束并重新固定走向，添加防护波纹管，故障码清除后未再出现。
BYD DTC AI Analysis

Insufficient refrigerant caused abnormal current fluctuations in the compressor.

✓
DTC B2AB0-49 appeared with B2A0300 (abnormal compressor speed). Inspection found a refrigerant leak at the high- and low-pressure line connections, causing excessive current fluctuation when the compressor ran at low frequency and triggering a false report from the sampling circuit. Recharged the refrigerant and repaired the leak, then reset the compressor control parameters using a diagnostic scanner.
BYD DTC AI Analysis

Software false positive (phantom DTC)

✓
2018 Qin PRO DM intermittently set DTC B2AB0-49 after the multimedia system upgrade. Wiring checked normal. Data stream confirmed current sampling values were normal. Identified as AC controller (AC ECU) software bug. Executed 'AC Controller Program Update' via VDS (V1.2 to V1.4). Fault cleared.
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.