AU
B2ABA-1C

DTC B2ABA-1C indicates a fault in the internal low-voltage power conversion module of the Electric Air Conditioning Compressor (EAC) controller — Seal U

Thermal Management System

DTC B2ABA-1C indicates a fault in the internal low-voltage power conversion module of the Electric Air Conditioning Compressor (EAC) controller.

The compressor controller converts the vehicle 12V low-voltage DC power into lower voltages, such as 5V and 3.3V, to power the internal MCU, CAN transceiver, position sensor, and drive circuit.

If the internal DC-DC conversion circuit, voltage regulator chip, or related filter capacitors experience a short circuit, open circuit, or abnormal voltage output (overvoltage or undervoltage), the compressor control unit fails its self-check and reports this fault.

This fault prevents the compressor from starting or causes a sudden shutdown during operation, affecting air conditioning cooling and battery/motor thermal management functions.

This condition typically does not shut down the high-voltage system; the vehicle remains drivable with caution.

5
Cases Logged
5
Causes
Likely Causes — Seal U
  • 1Overheating damaged the 12V-5V DC-DC conversion chip or power management IC inside the compressor controller, commonly due to prolonged high-load operation or poor heat dissipation conditions.
  • 2Loose connection in the external low-voltage power supply circuit, poor fuse contact, or excessive voltage fluctuation, causing the internal power module to repeatedly cycle on and off or sustain overload damage.
  • 3Compressor internal drive board capacitor aging and breakdown, or inductor open circuit, causing a load short circuit in the power conversion circuit.
  • 4Water ingress and corrosion in the low-voltage wiring harness connector (commonly due to improper front compartment cleaning or wading), causing a micro-short circuit between pins or a supply voltage drop.
  • 5Outdated compressor software and a flawed power management strategy cause false detection of a power supply fault under specific operating conditions.
What To Do
  • 1
    Use the BYD VDS or a dedicated diagnostic tool to read the complete fault codes and freeze frame data. Confirm if other related fault codes (such as communication or overheating faults) accompany B2ABA-1C.
  • 2
    Check the A/C compressor low-voltage supply fuse (usually 10A-15A) and relay in the front compartment fuse box. Measure their continuity and contact resistance.
  • 3
    Disconnect the compressor low-voltage connector and inspect the pins for corrosion, push-out, or burning. Measure the 12V supply voltage at the wiring harness side (standard value: 10.5V-16V, ignition ON) and the ground resistance (< 1Ω).
  • 4
    If the external power supply is normal, measure the resistance between the internal power terminal and the ground terminal of the compressor low-voltage connector. A short circuit indicates a faulty compressor internal power module.
  • 5
    Recover the air conditioning system refrigerant (R134a or R1234yf), remove the high-voltage service disconnect and apply insulation, then remove the faulty compressor assembly.
  • 6
    Replace the electric air conditioning compressor assembly (most BYD models integrate the compressor and controller, preventing separate repair of the controller board). Verify the new part number and software version match.
  • 7
    Install the new compressor and tighten the high-pressure pipe fittings to the specified torque (usually 25-35 Nm). Install new O-rings and apply refrigerant oil.
  • 8
    Use a vacuum pump to evacuate the air conditioning system for at least 15 minutes. The vacuum level must reach -0.1 MPa or lower. Hold the vacuum for 5 minutes to confirm no leaks.
  • 9
    Charge refrigerant to the amount specified on the vehicle nameplate (typically 450-550g for Qin EV). Use a diagnostic tool to execute the 'compressor replacement matching' or 'online coding' procedure to write the new compressor serial number and parameters.
  • 10
    Clear the fault code, start the vehicle, and set the air conditioning to maximum cooling mode. Observe the compressor speed, high-pressure line pressure, and air outlet temperature. Confirm the fault code does not return.
Real-World Cases
BYD DTC AI Analysis

BYD Qin EV300 AC suddenly stopped cooling; compressor low-voltage power supply module failed

✓
A 2017 Qin EV300 with 80,000 km: the owner reported the AC suddenly stopped cooling while driving; restarting did not help. The technician connected VDS and retrieved DTC B2ABA-1C. External 12V supply checked normal. The compressor low-voltage connector measured 12.4V, but the control board had no 5V output. Diagnosed: failed internal power-conversion module. The Qin EV300 uses an integrated electric compressor, so the controller cannot be replaced separately. The technician recovered the refrigerant, replaced the compressor assembly, charged 480g of refrigerant, and performed online matching; fault resolved.
Original source ↗
BYD DTC AI Analysis

Qin Pro DM thermal management system fault with air conditioning failure

✓
2018 BYD Qin Pro DM. After parking and restarting, the instrument cluster displayed "Check Thermal Management System" and the AC failed to cool. A diagnostic scan revealed DTC B2ABA-1C (Internal Low Voltage Power Supply Fault). Inspection found green corrosion on the compressor low-voltage harness connector (from prior water exposure), causing excessive contact resistance on the 12V supply pin (measured 8.2V). Prolonged undervoltage burned out the compressor's internal power module. Servicing the corroded harness terminals and replacing the compressor assembly returned the AC and thermal management system to normal.
Original source ↗
BYD DTC AI Analysis

Intermittent compressor fault on new Yuan Plus (Atto 3)

✓
A 2022 Yuan Plus with 12,000 km. The owner reported intermittent AC cooling failure in hot weather. When the fault occurred, the scan tool retrieved DTC B2ABA-1C; freeze frame data showed an ambient temperature of 42°C. The technician found severely blocked condenser fins, causing compressor compartment temperatures to exceed 85°C. The internal power module overheated and failed after thermal protection activated. We cleaned the condenser and replaced the compressor, and advised the owner to regularly clean the front compartment radiators. The fault has not recurred.
Original source ↗
BYD DTC AI Analysis

Qin Pro EV A/C compressor controller software fault

✓
2019 Qin Pro EV set DTC B2ABA-1C and the AC stopped working after 4S shop service. Checked external power supply and wiring—no faults found; compressor terminal voltage normal. Suspected a software fault and upgraded the AC controller and compressor control software to the latest version (higher than 2019-A3). The upgrade cleared the fault code and restored compressor operation. This case shows some B2ABA-1C faults can be fixed with a software update instead of replacing hardware.
Original source ↗
BYD DTC AI Analysis

Reference case for similar low-voltage power supply faults on Dolphin models

✓
Similar to faults seen in BYD Dolphin models, the air conditioning failed completely after the vehicle sat overnight. The diagnostic tool showed an internal low-voltage power supply fault (same definition as B2ABA-1C). Testing revealed the filter capacitor in the compressor's internal 12V-5V power supply module had failed, causing excessive ripple on the 5V output and resetting the control chip. Replaced the electric compressor assembly under warranty. After replacement, used the diagnostic tool to perform 'new compressor initialisation' and 'refrigerant quantity adaptive learning'. Full air conditioning function restored.
Original source ↗
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.