AU
B2AB2-49

This fault code indicates the IPM (Intelligent Power Module) inside the air conditioning compressor controller detects an IGBT (Insulated Gate Bipolar Transistor) malfunction — Seal U

Thermal Management System

This fault code indicates the IPM (Intelligent Power Module) inside the air conditioning compressor controller detects an IGBT (Insulated Gate Bipolar Transistor) malfunction.

In the BYD thermal management system, the electric compressor operates on a high-voltage DC drive.

The IPM module inverts the high-voltage DC into three-phase AC to drive the compressor motor.

DTC B2AB2-49 indicates the controller detects a hardware-level fault in the power semiconductor device.

Possible causes include a triggered IGBT overcurrent protection, module overheating (junction temperature exceeding 150°C), an upper and lower bridge arm shoot-through short circuit, abnormal gate drive voltage, or activation of the IPM internal self-protection circuit (FO fault output).

This fault shuts down the compressor, affecting cabin cooling and battery pack thermal management (liquid cooling).

In extreme cases, it can trigger a protective disconnection of the high-voltage system.

4
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1IPM/IGBT power module thermal or electrical breakdown: prolonged high-load operation, poor heat dissipation due to insufficient refrigerant, or excessive internal junction temperature damaging the IGBT chip.
  • 2Compressor motor winding fault: Stator winding inter-turn short circuit or insulation failure to ground (insulation resistance below 2MΩ), causing power module output overcurrent.
  • 3Compressor controller drive circuit fault: Burnt gate drive resistor, damaged drive optocoupler/isolation chip, or failed bootstrap capacitor causing abnormal IGBT drive waveform.
  • 4High-voltage power supply system fault: Poor contact in the High Voltage Interlock Loop (HVIL), precharge failure, or excessive DC bus voltage fluctuation (exceeding the 450V rated range) triggering IPM overvoltage protection.
  • 5Control board to power board connection fault: Pin header oxidation, cold solder joints, or a loose connector causing drive signal loss or false protection triggering.
What To Do
  • 1
    Diagnostic tool check: Use VDS or BYD Diagnosis to read all fault codes. Check for related faults such as B2AB149 (motor phase loss) and B2AC349 (compressor overcurrent). Record freeze frame data (high voltage, compressor speed, IGBT temperature).
  • 2
    Visual and wiring harness inspection: Check the compressor controller low-voltage connector (8PIN/12PIN) for water ingress, oxidation, or backed-out terminals; check the high-voltage wiring harness (HV+, HV-) insulation for damage, and verify the tightening torque meets the 9N·m standard.
  • 3
    Insulation resistance test: Disconnect the high-voltage service disconnect, wait 5 minutes, then measure the insulation resistance between the compressor three-phase terminals and the housing. The normal value is >500MΩ (1000V megohmmeter). A reading below 20MΩ indicates motor winding insulation failure.
  • 4
    Winding resistance measurement: Use a micro-ohmmeter to measure the compressor three-phase winding resistance (U-V, V-W, U-W). Normal value: 0.5-2.0Ω (varies by model). Three-phase imbalance rate must be <10%. Excessive deviation indicates an internal winding short circuit.
  • 5
    Controller disassembly and inspection (if repairable): Disassemble and inspect the IPM module. Measure the resistance between the IGBT gate and emitter (G-E); normal resistance is tens of kΩ. Inspect the gate drive circuit resistors and capacitors for burn marks. Measure the NTC temperature sensor resistance (approximately 10 kΩ at 25°C).
  • 6
    Component replacement: If diagnostics confirm IPM module damage or motor failure, replace the electric compressor assembly (BYD 4S dealers generally do not repair the controller separately; replace the complete compressor). For wiring harness or connector faults, repair the wiring harness and apply conductive grease.
  • 7
    System restoration: After replacement, evacuate the system using standard procedures (vacuum level ≤ -95 kPa, hold for 15 minutes). Charge the system with R134a or R1234yf refrigerant to the nameplate capacity (usually 450-550 g). Check the high and low-side pressures (low pressure 0.15-0.25 MPa, high pressure 1.2-1.6 MPa).
  • 8
    Function verification: Clear the fault code, power on the vehicle, and perform the air conditioning self-diagnosis (some models require compressor initialization learning). Test the cooling performance in ECO and SPORT modes. Read the live data stream to confirm the IGBT temperature is <85°C and the compressor speed shows no abnormal fluctuations.
Real-World Cases
BYD DTC AI Analysis

Qin Pro EV AC Compressor IPM Thermal Breakdown Replacement Case

✓
A 2019 Qin Pro EV with 68,000 km showed "Air Conditioning System Fault" on the dash. Retrieved codes B2AB2-49 (IPM/IGBT fault) and B2AC349 (compressor overcurrent). Inspection revealed critically low refrigerant (only 80 g remaining), causing the compressor to run dry with inadequate lubrication for an extended period. The IPM module heatsink temperature exceeded 120°C, resulting in thermal breakdown of the IGBT chip. Three-phase winding-to-ground insulation resistance measured 0.5 MΩ (failed). Replaced the electric compressor assembly, flushed the air conditioning lines, replaced the receiver drier, and recharged the system with 500 g refrigerant and 150 mL compressor oil. No recurrence after one month.
BYD DTC AI Analysis

Qin EV300 false IPM fault caused by loose high voltage interlock connection

✓
2017 Qin EV300. Intermittent B2AB2-49, AC intermittent. Compressor HVIL resistance measured intermittent open (should be continuous). Disassembled HV connector: interlock terminal spring fatigued, poor contact. This caused intermittent HV power loss; IPM detected bus voltage drop and set the fault. Repair: Replaced HV harness connector (P/N: BYD-ME-000123), re-crimped terminals, applied HV insulating silicone grease. No recurrence.
BYD DTC AI Analysis

Qin PRO DM Compressor Controller Driver Board Repair Case

✓
2018 BYD Qin Pro DM. AC not cooling at all; DTC B2AB2-49 present and will not clear. Compressor three-phase winding resistance measured normal at 1.2Ω with balanced phases; insulation resistance >1000MΩ, ruling out motor failure. Disassembled compressor controller (IPM module and driver board are of split design). Found gate drive resistor (10Ω/1W) burned black and open-circuit, causing loss of drive voltage to the IGBT gate. Replaced with same-specification resistor and adjacent 100nF decoupling capacitor, reapplied thermal grease, and reinstalled. Post-installation test: compressor runs smoothly, current 4-6A normal, fault resolved.
BYD DTC AI Analysis

BYD Qin EV300: Refrigerant overcharge triggers IPM overvoltage protection

✓
A Qin EV300 developed fault B2AB2-49 the day after service at an unauthorized repair shop. The owner reported the shop had performed an air-conditioning "deep service" and topped up the refrigerant. Testing showed the system contained 750g of refrigerant (standard 500g), causing excessive compressor discharge pressure (2.8MPa) and triggering IPM current-overload protection. Solution: Recovered excess refrigerant to specification, checked expansion valve opening, and cleaned poplar fluff from the condenser surface. Pressures normalized (low 0.2MPa, high 1.5MPa) and the fault code cleared automatically.
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.