AU
B2A6600

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

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.

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Cases Logged
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Causes
Likely Causes — Qin Plus
  • 1High Voltage Interlock Loop (HVIL) open circuit, backed-out pin, or poor contact, causing the system to falsely detect an abnormal high-voltage module connection.
  • 2Thermal management system temperature sensor fault (battery pack coolant inlet temperature, motor coolant temperature, air conditioning system temperature out of range), triggering over-temperature protection logic.
  • 3CAN bus communication fault, specifically loss, data error, interference, or transmission delay of message 244 (air conditioning/thermal management status message)
  • 4Internal control board fault in the electric compressor or PTC heater causes the actual status to mismatch the OK status in the feedback message (false OK).
  • 5Software version mismatch or control logic conflict between the air conditioning controller and the BMS causes incorrect status judgment.
What To Do
  • 1
    Connect the VDS diagnostic tool, read the complete fault codes and data stream, and check for accompanying fault codes: B2A6700 (compressor start failure), U-series communication faults, or temperature sensor faults.
  • 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 (rule out abnormal values such as -40°C or 150°C).
  • 4
    Check CAN communication: Measure the resistance (standard 60Ω) and voltage (CAN-H 2.5-3.5V, CAN-L 1.5-2.5V) of the CAN-H and CAN-L lines 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 wiring harness (>500MΩ), inspect the PTC heater high-voltage connector for burn damage, and confirm the high-voltage component self-test program version.
  • 6
    Perform software matching: Verify the ACU, BMS, and thermal management controller software versions are the latest. Upgrade 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 Qin Plus 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.