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) — Atto 8

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).

The B2AB41D fault code on the Atto 8 indicates the electric scroll compressor is drawing more current than the control unit allows, so it shuts down to protect the system. Severity is medium, as it can affect cabin heating/cooling and battery cooling. Common causes include an internal compressor motor winding short or a faulty integrated compressor controller. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
4
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Inter-turn short circuit in the electric compressor internal motor winding, or reduced phase-to-phase insulation (insulation resistance <20MΩ), 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 abnormal gate drive circuit causing three-phase drive waveform distortion.
  • 3Excessive mechanical load in the air conditioning system, such as refrigerant overcharge (exceeding the standard value of 550g±25g), receiver-drier/expansion valve blockage causing excessive high-side pressure (>2.5MPa), internal compressor mechanical seizure, or lack of refrigerant oil (POE oil) causing poor lubrication.
  • 4High-voltage power supply circuit fault, including battery pack contactor burn damage 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 speed closed-loop PID parameters causing current surges, or refrigerant migration causing liquid slugging during sharp ambient temperature drops.
What To Do
  • 1
    Use the VDS2000/3000 diagnostic tool to read the complete fault codes and freeze frame data. Specifically record the following data 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 (°C), and fault occurrence count (Trip Counter).
  • 2
    Perform the standard high-voltage power-down procedure (turn off the ignition, 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 high and low side pressures (normal low pressure: 0.15-0.25 MPa; high pressure: 1.3-1.6 MPa). Verify no ice blockage, debris blockage, or excessive refrigerant. Check the sight glass to verify the refrigerant oil colour and foam condition.
  • 4
    Disconnect the compressor low-voltage connector (usually 8-pin or 12-pin). Use a micro-ohmmeter to measure the DC resistance of the three-phase windings (U-V-W) (standard value 0.8-1.5 Ω at 20°C) and calculate the three-phase imbalance (must be <5%). Use a megohmmeter to measure the insulation resistance from each phase to the housing (must be >20 MΩ).
  • 5
    Check the high-voltage interlock loop (HVIL) for continuity, measure the voltage drop across the high-voltage contactor contacts (should be <0.1V), check the compressor high-voltage wiring harness shield for proper grounding, 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 BC-8103020E or similar). For refrigerant issues, use a recovery machine to recover the refrigerant, replace the desiccant, evacuate the system to -0.1MPa, and hold pressure for 15 minutes. Recharge with the standard amount (450-550g, depending on the specific model) of R134a or R1234yf and the corresponding compressor oil (approx. 120-150ml).
  • 7
    After replacement, perform the compressor self-learning procedure (if applicable). Run an active test using the diagnostic tool to verify the compressor operates normally across the full speed range (1000-6000rpm), current stabilizes between 3-12A, and no abnormal noise occurs. Perform a 30-minute road test to verify the thermal management function and confirm the fault code does not recur.
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 Atto 8 Fault Codes
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.B110A02DTC B110A02 indicates the thermal management master control unit (HVAC ECU) or body control module (BCM) failed to receive valid CAN data frames from the PM2.5 air quality sensor over consecutive communication cycles (typically 500ms per cycle). The sensor typically mounts at the HVAC unit air inlet or behind the glove box and transmits real-time particulate concentration data (unit: μg/m³) to the HVAC controller via the CAN bus. The fault is essentially a communication link layer timeout. Potential causes include physical layer wiring faults, sensor power supply failures, sensor internal MCU lockup, or CAN network topology damage. Although this non-critical fault does not directly affect driving safety, it disables the intelligent air purification strategy and the automatic fresh air/recirculation switching function. In extreme cases, it triggers a thermal management system degraded mode, limiting compressor power or fixing the air flap position.B110B07This fault code indicates abnormal operation of the internal air pump (sampling pump) in the PM2.5 air quality detection module. The PM2.5 detector uses the laser scattering principle to measure particulate concentration and requires a built-in air pump to draw ambient air into the detection chamber at a constant flow rate. The ECU sets this code when it detects an open or short in the air pump drive circuit, abnormal current (stall or free-running), or abnormal speed feedback. This fault causes the automatic air conditioning system to lose air quality sensing capability, preventing automatic switching between fresh air and recirculation modes. The instrument cluster air quality display may show '--' or a fixed value, but the fault does not affect the vehicle powertrain or basic air conditioning cooling and heating functions.B173CDTC B173C indicates the Supplemental Restraint System (SRS) detects the Right Second Row Side Airbag squib circuit resistance exceeds the calibrated threshold (typically >4.5Ω). This fault is an active diagnostic result of the SRS system, indicating a high-resistance condition in the circuit between the Airbag Control Unit (ACU) and the airbag module. Causes for excessive resistance include increased contact resistance, a partially broken wiring harness, terminal oxidation, or an aging squib wire inside the airbag module. This fault causes the system to mark the airbag circuit as 'unreliable', meaning the airbag may fail to deploy during a collision. The fault typically illuminates the instrument cluster airbag warning light (SRS light) continuously, and some models also sound a warning buzzer.
Common problems reported for Atto 8 →Atto 8 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.