AU
B2A6600

This DTC indicates the vehicle control system disabled high-voltage components of the thermal management or air conditioning systems (e — Atto 3

Thermal Management System

This DTC indicates the vehicle control system disabled high-voltage components of the thermal management or air conditioning systems (e.g., electric compressor, PTC heater, battery chiller).

Trigger logic: When the air conditioning controller (ACU) or thermal management controller detects a high-voltage module status of "OK" or false "OK" (pseudo OK) via CAN bus message 244, it identifies a potential safety risk (such as a high-voltage interlock fault, over-temperature protection, or self-check failure with an incorrect status bit) and triggers the protection mechanism to cut off the high-voltage power supply.

Typical causes include loss of high-voltage interlock loop (HVIL) integrity, thermal management over-temperature protection, unsynchronized CAN communication data, or internal high-voltage component faults.

The B2A6600 fault code on the Atto 3 indicates the vehicle has disabled high-voltage parts of the thermal management or air conditioning system, such as the electric compressor, PTC heater, or battery chiller. Severity is medium. Common causes include a high-voltage interlock loop wiring or connector fault, or an over-temperature sensor/protection issue. The recommended fix is to visit an authorised dealer for diagnosis and repair. Typical repair cost data is available.
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Cases Logged
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Causes
Likely Causes — Atto 3
  • 1High-voltage interlock loop (HVIL) wiring open circuit, terminal back-out, or poor contact, causing the system to incorrectly detect an abnormal high-voltage module connection.
  • 2Thermal management system temperature sensor fault (battery pack coolant inlet temperature, motor coolant temperature, or air conditioning system temperature exceeds limits), triggering over-temperature protection logic.
  • 3CAN bus communication fault, specifically loss, data errors, interference, or transmission delays of message 244 (air conditioning/thermal management status message).
  • 4Electric compressor or PTC heater internal control board fault, causing the actual status to mismatch the OK status reported in the message (false OK).
  • 5Air conditioning controller and BMS software version mismatch or control logic conflict, causing incorrect status judgment.
What To Do
  • 1
    Connect the VDS diagnostic tool, read the complete fault codes and data stream, and check for accompanying B2A6700 (compressor start failure), U-series communication faults, or temperature sensor fault codes.
  • 2
    Check high-voltage interlock loop integrity: measure continuity at the HVIL pins on the low-voltage connectors of high-voltage components such as the electric compressor and PTC heater. Inspect the pins for push-out, oxidation, or water ingress.
  • 3
    Read the thermal management data stream: Verify the battery pack coolant inlet/outlet temperatures, motor coolant temperature, compressor discharge temperature, and PTC temperature are within normal ranges (exclude abnormal values such as -40°C or 150°C).
  • 4
    Check CAN communication: Measure CAN-H and CAN-L line resistance (standard 60Ω) and voltage (CAN-H 2.5-3.5V, CAN-L 1.5-2.5V) from the air conditioning controller (ACU) to the BMS. Verify normal transmission of message 244.
  • 5
    Check high-voltage component status: measure the insulation resistance of the electric compressor three-phase high-voltage harness (>500MΩ), inspect the PTC heater high-voltage connector for burn marks, and verify the high-voltage component self-test program version.
  • 6
    Perform software matching: Verify the ACU, BMS, and thermal management controller have the latest software versions. Update or synchronize configuration parameters if necessary.
  • 7
    Clear the fault code, perform a high-voltage power-on test, and observe the high-voltage module status bit changes in the 244 message data stream to confirm fault resolution.
Real-World Cases
BYD DTC AI Analysis

Qin Pro EV electric compressor HVIL pin retraction causing B2A6600

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Fault symptoms: AC not cooling, no warning lights on dash. Scanner shows DTC B2A6600. Diagnosis: Live data showed electric compressor status "OK" but the unit wasn't actually running. HVIL circuit was intermittently open. Removed and inspected the compressor low-voltage connector. Found the HVIL pin backed out approximately 2 mm, causing poor contact. The system registered a "false OK" and triggered protection. Repair: Reseated the pin. Verified HVIL circuit continuity resistance <1 Ω. Fault cleared.
BYD DTC AI Analysis

Qin Pro DM: PTC temperature sensor open circuit triggered high-voltage protection

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Symptoms: Vehicle drove normally, but heating and cooling both failed, with DTCs B2A6600 and B2A6700 logged. Diagnosis: Read the thermal management live data and found the PTC heater outlet temperature showed -40°C (sensor open circuit). The BMS determined an overheating risk and prohibited PTC operation via message 244, though the status bit incorrectly displayed OK (false OK). Resolution: Replaced the PTC heater assembly (integral temperature sensor). Fault resolved.
BYD DTC AI Analysis

Qin EV300: CAN Harness Wear Causes Message 244 Fault

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**Fault Description:** Intermittent AC operation. DTC B2A6600 intermittent, mainly on rough roads. **Diagnosis:** CAN bus waveform measurement revealed occasional error frames and packet loss on message 244 (AC controller to BMS). Harness inspection found the AC controller CAN wire chafed through at the firewall grommet, causing intermittent short to body. **Repair:** Repaired damaged CAN wiring, re-wrapped harness, installed anti-chafe sleeving, and adjusted harness mounting position.
BYD DTC AI Analysis

Qin Pro EV battery cooler inlet temperature sensor drift

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Fault symptom: Air conditioning automatically shuts off during fast charging with DTC B2A6600; operates normally while driving. Diagnosis: Live data showed the battery cooler inlet coolant temperature sensor reading 85°C (actual ambient temperature 30°C). Sensor signal drift caused the BMS to falsely detect battery overheating and disable the electric compressor. However, the AC controller still reported compressor status as OK (false OK). Solution: Replaced the battery cooler inlet coolant temperature sensor and calibrated the thermal management system.
Other Atto 3 Fault Codes
P0AA6Hybrid Battery Voltage System Isolation FaultB1108For 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.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.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.B173A1ADTC B173A1A indicates the right middle-row side airbag (typically located on the side of the right second-row seat or inside the C-pillar trim panel) igniter circuit resistance measures 0 Ω. In the Supplemental Restraint System (SRS), normal airbag igniter resistance ranges between 2.0 and 5.0 Ω. A resistance of 0 Ω indicates a short to ground or a short between circuit wires, preventing the Airbag Control Unit (ACU) from establishing a normal monitoring circuit. This safety-critical fault prevents the airbag from deploying during a collision, continuously illuminates the instrument panel SRS warning lamp, and may force the entire airbag system into fail-safe mode.
Common problems reported for Atto 3 →Atto 3 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.