AU
B2A6700

This DTC indicates the Electric A/C Compressor (EAC) fails to establish normal speed or pressure after multiple consecutive start attempts following a start command — Seal 6 EV

Thermal Management System

This DTC indicates the Electric A/C Compressor (EAC) fails to establish normal speed or pressure after multiple consecutive start attempts following a start command.

The system logs a start failure fault.

The root cause is the compressor controller failing to provide a valid speed signal within the specified time (typically 2-3 seconds) or failing to build torque.

On plug-in hybrid (DM) models, an electric compressor failure prompts the system to start the engine to drive the mechanical compressor (Belt-driven Compressor) as a backup cooling solution, triggering DTC B2A6700.

This fault causes a complete loss of A/C cooling capacity, which is particularly severe in pure electric mode.

Additionally, because the BYD thermal management system couples the battery chiller (Chiller) with the A/C system, a prolonged fault can cause power battery thermal management failure, triggering power limits or even high-voltage interlock disconnection.

5
Cases Logged
5
Causes
Likely Causes — Seal 6 EV
  • 1Abnormal high-voltage power supply to the electric compressor: Causes include a blown compressor fuse in the high-voltage distribution box, poor contact in the high-voltage interlock loop (HVIL), burnt main negative/positive contactors, or a damaged IPM module on the compressor internal motor drive board, preventing the compressor from receiving sufficient high-voltage DC power (typically 320V-750V).
  • 2Compressor mechanical seizure or motor fault: Internal scroll plate wear causing seizure, motor permanent magnet demagnetization, bearing seizure, or refrigerant oil degradation causes excessive starting torque, triggering controller overcurrent protection and causing a start failure.
  • 3Low-voltage control communication fault: LIN bus or CAN bus communication interruption (between the BMS, VCU, and compressor controller), abnormal wake-up signal, or enable signal circuit open or short to ground, preventing the compressor controller from receiving the correct speed command.
  • 4Refrigerant pressure protective shutdown: Severely insufficient system refrigerant (leakage) causes excessively low pressure on the low-pressure side, or a refrigerant overcharge/poor condenser heat dissipation causes excessively high pressure on the high-pressure side, triggering the pressure switch protection and preventing compressor startup.
  • 5Thermal Management System (TMS) controller or air conditioning controller software bug: Controller internal program logic error causes a false start-up failure report; or an overly sensitive algorithm threshold setting for the deviation between the compressor target speed and actual control value.
What To Do
  • 1
    Diagnostic tool reading and freeze frame analysis: Use VDS2000 or Launch X431 to read all fault codes. Check for accompanying high-voltage interlock faults (P0A0D, P0A0E) or insulation faults (P1A00 series). Record the ambient temperature, battery SOC, compressor target speed, and actual speed data streams at the time of the fault.
  • 2
    High-voltage safety inspection and insulation test: Disconnect the Manual Service Disconnect (MSD) and wait 5 minutes for high-voltage discharge. Use a megohmmeter to measure the insulation resistance to ground of the electric compressor high-voltage harness (standard >20MΩ). Check the high-voltage connectors for burning or backed-out pins. Measure the continuity of the high-voltage interlock circuit.
  • 3
    Low-voltage circuit and communication check: Disconnect the compressor low-voltage connector and measure the pins: constant power (B+) should be 12V, ground (GND) <0.1Ω, LIN line voltage approximately 9-11V (dynamic), and CAN-H/CAN-L voltage to ground around 2.5V. Use an oscilloscope to check the LIN bus waveform for distortion.
  • 4
    Refrigerant pressure and system sealing check: Connect a manifold gauge set and check the static pressure (R134a: approx. 0.6-0.8 MPa at 25°C). If the pressure is too low, evacuate the system using a vacuum pump, hold the vacuum for 30 minutes, and use an electronic leak detector to locate the leak (commonly found at the compressor shaft seal and high/low-pressure ports).
  • 5
    Compressor operation test and current monitoring: Restore the high-voltage connection, enter the scan tool actuator test mode, and gradually increase the compressor speed (1000rpm → 3000rpm → 6000rpm). Use a clamp meter to monitor the high-voltage current. The normal start-up current should be <15A and rise steadily. If the current is >40A, cut the power immediately. If the current exceeds 40A or oscillates, the compressor itself is faulty.
  • 6
    Controller software update and replacement: If all previous checks are normal, update the Thermal Management Controller (TMS) and compressor controller to the latest software version. If the fault persists, replace the electric compressor assembly. (Note: After replacement, add the specified ND-OIL8 refrigerant oil or equivalent, and perform the standard refrigerant charge.)
Real-World Cases
BYD DTC AI Analysis

Qin Pro DM: Backed-out HVIL pin causing intermittent no-start

✓
Intermittent A/C not cooling with DTCs B2A6700 and P0A0D (high voltage interlock fault). Found a backed-out pin in the HVIL circuit of the electric compressor high voltage connector; contact failed over bumps. Re-crimped the pin and applied conductive grease. Fixed. Common on 2018–2019 Qin Pro models due to weak retaining clips in early high voltage connector designs.
BYD DTC AI Analysis

IGBT module inside Qin EV300 compressor burnt out, causing complete failure.

✓
At 80,000 km, the AC failed completely. Scan tool showed DTC B2A6700. During actuator testing, the compressor did not respond and high-voltage side current read zero. Disassembled the compressor controller and found the internal IGBT power module burned out with visible burn marks on the driver board. Replaced the electric compressor assembly (part number: BC28-8103010) and refilled with 150 ml PAG 46 compressor oil and 450 g R134a refrigerant per specification. Fault resolved.
BYD DTC AI Analysis

Minor refrigerant leak triggered low-pressure protection, preventing startup

✓
Poor AC cooling in high summer temperatures. DTC B2A6700 logged. Data stream showed compressor stopped within 2 seconds of engagement, low-side pressure dropping below 0.15 MPa. Vacuum hold test and fluorescent leak detection found a minor leak at the battery cooler (Chiller) connection. Repaired the leak, replaced the receiver drier, evacuated and recharged the system. Pressures normalized (low side 0.2–0.3 MPa, high side 1.4–1.6 MPa). Fault resolved.
BYD DTC AI Analysis

LIN bus interference caused compressor controller communication fault.

✓
Aftermarket audio installation caused intermittent AC failure. Stored DTC B2A6700 with multiple LIN slave node communication faults. Found modified amplifier power wiring running parallel to the AC compressor LIN harness, causing electromagnetic interference. Re-routed wiring to separate power and signal lines (>30 cm apart) and installed a ferrite core filter on the compressor LIN line. Restored communication; fault has not reoccurred.
BYD DTC AI Analysis

Outdated thermal management controller software caused false fault detection.

✓
The 2019 Qin Pro EV frequently set DTC B2A6700 in cold conditions (-5°C), but the compressor ran normally. Live data revealed the controller was overly sensitive to compressor speed overshoot. Upgraded the TMS controller software to the latest version (3.00.15 or above) via VDS2000, adjusting the startup failure threshold. The fault cleared. This is BYD's official software optimisation fix.
Other Seal 6 EV 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.