AU
B2ABA1C

DTC B2ABA1C indicates a fault in the internal low-voltage DC power conversion module of the electric air conditioning compressor (E-Compressor) controller — Seal U

Thermal Management System

DTC B2ABA1C indicates a fault in the internal low-voltage DC power conversion module of the electric air conditioning compressor (E-Compressor) controller.

This module converts the vehicle 12V battery voltage to 5V/3.3V to power the main control MCU, temperature sensor, current sensor, and LIN/CAN communication chips on the compressor control board.

The controller sets this code when the internal DC-DC conversion circuit output voltage falls outside the permitted range (typically below 4.5V or above 5.5V), triggers short-circuit protection, or sustains a MOSFET breakdown.

This fault disables the compressor control logic and prevents it from responding to air conditioning start commands.

This directly affects cabin cooling/heating and the battery pack liquid cooling circuit, but does not compromise high-voltage drive system safety.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Aging or breakdown of the MOSFET or filter capacitor in the compressor controller internal DC-DC power module, causing abnormal 5V output.
  • 2Intermittent open circuit or voltage fluctuation (below 9V or above 16V) in the 12V low-voltage supply line triggers a protective lockout of the internal power module.
  • 3Compressor controller seal failure allows condensate or moisture intrusion, causing a short circuit or corrosion on the internal circuit board.
  • 4Controller PCB soldering defect (cold solder joints in specific batches), causing an open circuit after prolonged thermal cycling.
  • 5Under extreme operating conditions, controller overheating (poor heat dissipation) triggers internal power supply thermal protection or causes component thermal damage.
What To Do
  • 1
    Connect the BYD dedicated diagnostic tool (ED-400 or Launch X-431), read the complete DTC freeze frame data, and confirm B2ABA1C is a current fault (Present), not a history fault.
  • 2
    Check the compressor low-voltage connector: measure the 12V supply voltage (PIN1/2) to verify it is between 12.0 and 14.5V. Verify the LIN line (PIN3) resistance to ground is approximately 60Ω. Inspect the connector for backed-out pins, oxidation, or signs of water ingress.
  • 3
    Read data stream: Check parameters such as compressor controller internal temperature (normal <70°C), high-voltage side voltage (320V-420V), and IGBT temperature to rule out related faults.
  • 4
    Disconnect the compressor low-voltage connector and use an oscilloscope to check the 12V power supply ripple. If the ripple voltage is >500mV, first inspect and repair the front compartment power distribution box or the BCM power supply circuit.
  • 5
    If the external power supply is normal, diagnose an internal fault in the compressor controller. BYD electric compressors use a fully sealed integrated design; therefore, the internal power module is not separately serviceable. Replace the compressor assembly (part numbers vary by vehicle model, e.g., BC28E-8103020 for the Qin EV).
  • 6
    After replacement, perform the following: ① evacuate the system using a vacuum pump (hold at <-95 kPa for 10 minutes); ② charge R134a refrigerant to standard specification (usually 450–550 g); ③ use a diagnostic tool to execute the 'A/C system initialization' or 'compressor self-learning' procedure; ④ perform a road test and observe compressor speed response and high-voltage interlock status.
Real-World Cases
BYD DTC AI Analysis

Qin Pro EV compressor internal power module breakdown

✓
Vehicle AC suddenly stopped cooling. No warning lights on the instrument cluster, but the AC panel flashed. Scan tool retrieved DTCs B2ABA1C (current fault) and B2AB573 (startup failure). Measured compressor HV at 320V (normal), 12V supply normal, LIN signal normal. Disassembled the compressor controller; internal 5V DC-DC module output measured only 1.2V and the MOSFET had shorted. Replaced the electric compressor assembly; fault resolved. Old unit analysis confirmed the power module filter capacitor had insufficient voltage rating, causing breakdown—a quality issue from an early production batch.
BYD DTC AI Analysis

Intermittent B2ABA1C and high temperature protection on Song PLUS EV

✓
Owner reported AC cutting in and out during hot weather; fixed by restarting. Intermittent DTC B2ABA1C accompanied by B2AB64B (internal temperature abnormal). Found compressor mounted too close to exhaust manifold with poor heat dissipation. Data stream showed controller temperature reaching 85°C triggered protection. Disassembly revealed bulging, leaking electrolytic capacitor in internal power module and excessive compressor bearing resistance. Replaced compressor and optimized mounting bracket (added thermal insulation pad). Issue resolved.
BYD DTC AI Analysis

BYD Yuan Plus batch low-voltage power supply defect recall

✓
Certain batches of Yuan Plus (SC2E) suffered clustered AC cooling failures. Diagnostics reported DTC B2ABA1C. BYD confirmed via technical bulletin that specific supplier batches of the compressor controller PCBA had cold solder joints, causing the internal power module to open-circuit under vibration. The manufacturer issued a technical upgrade, replacing compressors on faulty vehicles with improved versions (controller V2.3 or higher) free of charge and extending the warranty on related components.
BYD DTC AI Analysis

BYD Dolphin New Car Early Failure Warranty Claim Case

✓
AC failed at 4,800 km. DTC B2ABA1C present. Checked high-voltage interlock and 12V supply — both normal. 12V input at the compressor low-voltage connector measured normal, but the LIN line had no signal feedback (should send periodic messages). Diagnosed a manufacturing defect in the compressor controller's internal power module that prevented the MCU from starting. Processed the warranty claim, replaced the compressor assembly and recharged the refrigerant. Fault resolved.
BYD DTC AI Analysis

e-Platform 3.0 Vehicle Software False Alarm Troubleshooting

✓
Found history DTC B2ABA1C at routine service. Owner reported no AC issues. No active faults present; compressor operating normally. Early software version produces false codes during voltage fluctuations (e.g., jump-starting a discharged battery). Cleared codes, updated compressor controller software to latest version via VDS2000, and checked 12V battery health (replace if SOC < 50%).
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.