AU
B2AB049

DTC B2AB049 indicates a malfunction in the current sampling circuit of the electric compressor drive controller in the thermal management system — Seal U

Thermal Management System

DTC B2AB049 indicates a malfunction in the current sampling circuit of the electric compressor drive controller in the thermal management system.

This circuit typically uses a Hall effect sensor or a precision shunt resistor to monitor the compressor motor operating current in real time, enabling overcurrent protection, closed-loop torque control, and stall detection.

The controller sets this fault when it detects a sampled value outside the valid range (e.g., signal line open circuit, short to ground or power, sampled value continuously at zero or saturated, or an abnormal three-phase current vector sum).

When this fault occurs, the compressor initiates a protective shutdown, disabling the air conditioning cooling and heating functions.

If the vehicle uses a heat pump system or relies on the air conditioning system for battery cooling, prolonged operation may overheat the battery or motor, but generally does not directly affect driving safety.

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Cases Logged
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Causes
Likely Causes — Seal U
  • 1The internal Hall current sensor in the electric compressor controller is damaged or has cracked solder joints, causing sampled signal drift or interruption.
  • 2Backed-out terminals, water ingress, or oxidation at the compressor low-voltage wiring harness connector (usually an 8-pin or 12-pin plug), causing excessive contact resistance in the sampling signal wire.
  • 3Inter-turn short circuit in the compressor motor windings or three-phase imbalance distorts the actual current waveform, triggering abnormal sampling protection.
  • 4Filter capacitor leakage in the controller internal sampling circuit, damaged operational amplifier chip, or reference voltage drift
  • 5Poor contact in the compressor controller low-voltage power supply (constant +12V) or ground circuit, causing unstable operating voltage in the sampling circuit.
What To Do
  • 1
    Use VDS2000 or the BYD dedicated diagnostic tool to read the complete fault codes and freeze frame data. Check for accompanying codes B2AA000 (compressor communication fault) or B2AB149 (compressor drive fault). Check if 'compressor phase current' and 'bus current' in the data stream display 0, 65535, or abnormal fluctuations.
  • 2
    Verify the locking mechanism of the front compartment electric compressor controller low-voltage connector is intact. Visually inspect the pins for green copper corrosion, burn marks, or backed-out pins. Measure the voltage to ground of the current sampling signal wire (usually a thin wire of a specific colour; refer to the Qin EV wiring diagram). Normal static voltage is approximately 2.5V bias or 0V; compare this reading against the standard value in the repair manual.
  • 3
    Disconnect the compressor high-voltage service switch, wait 5 minutes, then measure the insulation resistance between the compressor three-phase high-voltage cables and the housing (standard value >500MΩ). If the insulation resistance is low, replace the compressor. Measure the three-phase winding resistance and confirm the balance is <5%.
  • 4
    If the wiring and compressor assembly are normal, use an oscilloscope to verify the controller outputs the current sampling PWM signal or analog voltage signal to the MCU. If the signal is missing but wiring continuity is normal, the compressor controller board is faulty.
  • 5
    Replace the electric compressor assembly (Qin EV 2019 uses an integrated compressor; the controller and motor are not serviced separately), add the specified amount of refrigerant oil (POE68) and refrigerant, evacuate the system using a vacuum pump (hold -0.1MPa for 30 minutes), and tighten the high-pressure connection to the standard torque (usually 25-30N·m).
  • 6
    Clear the fault code. Start the vehicle and set the air conditioning to maximum cooling mode. Observe whether the current sampling value in the data stream changes linearly with the rotational speed (normal range approximately 0-15A) to confirm the fault is resolved.
Real-World Cases
BYD DTC AI Analysis

Current sampling fault restricts EV mode on Qin 80

✓
A BYD Qin 80 hybrid displayed "Check Power System" on the instrument cluster and would not drive in EV mode. Scanning revealed DTC B2AB049 (current sampling fault). Inspection found the current sampling harness connector between the Battery Information Collector (BIC) inside the high-voltage battery pack and the Battery Management System (BMS) had come loose, interrupting the Hall current sensor signal. The technician reseated the connector and applied conductive grease to secure it. After clearing the code, EV mode returned to normal. This case shows that B2AB049 can also indicate BMS-related faults in certain models.
Original source ↗
BYD DTC AI Analysis

Qin EV compressor controller sampling circuit burned out

✓
A 2019 Qin EV with 80,000 km suddenly lost air conditioning while driving; restart did not help. The diagnostic tool showed current sampling fault B2AB049. Disassembling the electric compressor revealed burn damage to the current sensor power supply circuit inside the controller, with scorch marks on the PCB. Compressor three-phase winding resistance measured approximately 1.2Ω and balanced, with good insulation. Diagnosed as internal short circuit in the controller. Replaced the electric compressor assembly and recharged the refrigerant. Fault cleared.
BYD DTC AI Analysis

Intermittent current sampling fault on rough roads

✓
Air conditioning occasionally cuts out when driving over speed bumps but functions normally on flat roads. Read historical DTC B2AB049. Found an intermittent connection at pin 5 (current sampling signal terminal) of the compressor controller low-voltage harness connector. Gently wiggling the harness by hand reproduced the fault. Replaced the compressor low-voltage harness connector and re-secured the harness routing to prevent interference with the body. Fault has not recurred.
BYD DTC AI Analysis

Aftermarket inverter causing current sampling interference

✓
Owner reported that after installing an aftermarket inverter, the A/C system intermittently threw code B2AB049; the fault returned several days after clearing. Inspection found the inverter negative ground shared a chassis ground point with the compressor controller. High-power inverter operation created ground bounce noise that interfered with the current sampling signal. Ran a dedicated ground wire from the inverter directly to the battery negative terminal and added a ferrite core filter to the compressor signal line. Fault eliminated permanently.
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.