AU
B2AB249

DTC B2AB249 indicates a fault in the IGBT (Insulated Gate Bipolar Transistor) power device or drive circuit inside the electric air conditioning compressor drive module (IPM, Intelligent Power Module) — Atto 8

Thermal Management System

DTC B2AB249 indicates a fault in the IGBT (Insulated Gate Bipolar Transistor) power device or drive circuit inside the electric air conditioning compressor drive module (IPM, Intelligent Power Module).

In models such as the BYD Qin EV, high-voltage DC drives the electric compressor.

The IPM converts this high-voltage DC power into three-phase AC power to drive the compressor motor.

IGBT overcurrent, overtemperature, overvoltage, or an internal module short circuit typically triggers this fault, initiating compressor shutdown protection.

This affects air conditioning cooling/heating functions and battery thermal management capabilities.

This is a hardware-level fault; in most cases, a power reset cannot permanently clear it.

5
Cases Logged
5
Causes
Likely Causes — Atto 8
  • 1Poor heat dissipation in the electric compressor drive module (IPM) or cooling circuit blockage causes the IGBT junction temperature to exceed the protection threshold (usually >150°C).
  • 2IGBT power device breakdown or aging due to compressor motor winding short circuit, insulation failure, or high-voltage surge.
  • 3Internal fault in the compressor controller current detection circuit triggers a false overcurrent fault.
  • 4High-voltage power supply system fault, such as unstable PDU (high-voltage distribution box) output voltage or precharge failure causing abnormal IPM input voltage.
  • 5Compressor mechanical seizure stalls the motor, triggering IGBT overcurrent protection.
What To Do
  • 1
    Use the VDS2000/VDS2100 diagnostic tool to read complete fault codes and freeze frame data. Record key parameters at the time of the fault, including compressor speed, high voltage, and IGBT temperature.
  • 2
    Check the electric compressor high-voltage wiring harness connector (usually located on the top or side of the compressor) for burning or looseness, and measure the continuity of the high-voltage interlock circuit.
  • 3
    Measure the insulation resistance between the compressor high-voltage terminal and the vehicle body. The standard value is ≥20MΩ (500V megohmmeter). If insulation fails, replace the compressor assembly.
  • 4
    Check the compressor controller low-voltage power supply: verify normal voltage at the 12V constant power (B+), ignition switch signal (IG), and ground wire (GND), and rule out poor connections.
  • 5
    For water-cooled compressor models (some Qin EV batches), inspect the compressor controller cooling water lines for blockages and verify water pump operation to ensure normal IPM heat dissipation.
  • 6
    Perform the compressor Active Test and observe if it starts normally. Simultaneously read the deviation between the actual and target current. If the system reports a fault immediately upon startup, the IPM hardware is damaged.
  • 7
    Replace the electric compressor assembly (BYD genuine part number usually HA-8103020 series). After replacement, perform: ① evacuate and recharge refrigerant (R134a, standard quantity approximately 450-550g); ② compressor break-in procedure; ③ air conditioning system leak test.
Real-World Cases
BYD DTC AI Analysis

Qin EV AC intermittent cooling failure, IPM overtemperature protection

✓
2019 Qin EV, 68,000 km. Customer reported the AC suddenly stopped working during high-speed driving or fast charging, recovering after 30 minutes parked. Scanner retrieved history DTC B2AB249; freeze frame showed IPM temperature reached 165°C at failure. Inspection found airlock in compressor controller cooling circuit; water pump ran but flow was insufficient. After bleeding and flushing the circuit, road testing showed IPM temperature stabilised at 85-95°C. Fault resolved.
BYD DTC AI Analysis

After replacing the compressor, the IPM fault kept recurring due to a backed-out high-voltage interlock pin.

✓
Had the electric compressor replaced at a non-authorised service centre. The vehicle kept setting DTC B2AB249 and the code wouldn't clear. Found the HVIL (High Voltage Interlock Loop) pin in the new compressor's high voltage connector had backed out due to improper installation, causing intermittent opens in the high voltage interlock circuit. The IPM set a protective fault code when it detected the HVIL abnormality. Reseated the high voltage connector and secured the locking tab. The fault code cleared and air conditioning returned to normal.
BYD DTC AI Analysis

IGBT module breakdown caused complete air conditioning failure

✓
2019 Qin EV, total AC failure. Active DTC B2AB249 returned immediately after clearing. Measured normal insulation resistance between compressor three-phase windings and housing, but active testing produced no compressor response and zero HV-side current. Disassembled the compressor controller and found the V-phase IGBT upper and lower bridge arms in the IPM module shorted. Replaced the electric compressor assembly; fault resolved. Old part analysis confirmed IGBT thermal fatigue failure.
BYD DTC AI Analysis

IPM fault triggered after fast charging due to abnormal PDU output voltage.

✓
Fault code B2AB249 set after using certain third-party DC fast chargers. Data analysis showed the PDU output voltage spiked to 480V instantly at fast-charging completion (normal range 320-420V), exceeding the IPM overvoltage protection threshold (~450V). Checked the fast charging port, high-voltage distribution box (PDU), and compressor controller high-voltage input capacitor; confirmed a loose internal pre-charge resistor connection in the PDU caused the voltage surge. Replaced the PDU and reflashed the compressor controller software (raised the voltage withstand threshold).
BYD DTC AI Analysis

Compressor mechanical seizure triggered IGBT overcurrent protection.

✓
At 82,000 km, DTC B2AB249 recurred with AC activation, accompanied by abnormal compressor noise. Disassembly revealed worn scroll plates generating metal debris, increasing motor resistance torque. Starting current exceeded the IGBT rating (peaking at approximately 60 A), triggering protection. Replaced the electric compressor assembly and flushed the AC lines to prevent debris from entering the new compressor. System returned to normal. Advised customer to check refrigerant levels regularly to prevent poor lubrication.
Other Atto 8 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.